iphone.c

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/*
 * Copyright (C) 2020 Michael Brown <mbrown@fensystems.co.uk>.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301, USA.
 *
 * You can also choose to distribute this program under the terms of
 * the Unmodified Binary Distribution Licence (as given in the file
 * COPYING.UBDL), provided that you have satisfied its requirements.
 */

FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );

#include <stdint.h>
#include <string.h>
#include <stdio.h>
#include <errno.h>
#include <ipxe/netdevice.h>
#include <ipxe/ethernet.h>
#include <ipxe/if_ether.h>
#include <ipxe/profile.h>
#include <ipxe/base64.h>
#include <ipxe/sha256.h>
#include <ipxe/rsa.h>
#include <ipxe/x509.h>
#include <ipxe/pem.h>
#include <ipxe/xfer.h>
#include <ipxe/tls.h>
#include <ipxe/usb.h>
#include "iphone.h"

/** @file
 *
 * iPhone USB Ethernet driver
 *
 */

/* Disambiguate the various error causes */
#define EPIPE_NO_MUX __einfo_error ( EINFO_EPIPE_NO_MUX )
#define EINFO_EPIPE_NO_MUX                                              \
        __einfo_uniqify ( EINFO_EPIPE, 0x01,                            \
                          "No USB multiplexer" )
#define EINPROGRESS_PAIRING __einfo_error ( EINFO_EINPROGRESS_PAIRING )
#define EINFO_EINPROGRESS_PAIRING                                       \
        __einfo_uniqify ( EINFO_EINPROGRESS, 0x01,                      \
                          "Pairing in progress" )
#define ENOTCONN_DISABLED __einfo_error ( EINFO_ENOTCONN_DISABLED )
#define EINFO_ENOTCONN_DISABLED                                         \
        __einfo_uniqify ( EINFO_ENOTCONN, IPHONE_LINK_DISABLED,         \
                          "Personal Hotspot disabled" )
#define ENOTCONN_STATUS( status )                                       \
        EUNIQ ( EINFO_ENOTCONN, ( (status) & 0x1f ),                    \
                ENOTCONN_DISABLED )

static int ipair_create ( struct interface *xfer, unsigned int flags );

/** Bulk IN completion profiler */
static struct profiler iphone_in_profiler __profiler =
        { .name = "iphone.in" };

/** Bulk OUT profiler */
static struct profiler iphone_out_profiler __profiler =
        { .name = "iphone.out" };

/** List of USB multiplexers */
static LIST_HEAD ( imuxes );

/** List of iPhone network devices */
static LIST_HEAD ( iphones );

/******************************************************************************
 *
 * iPhone pairing certificates
 *
 ******************************************************************************
 */

/** iPhone root certificate fingerprint */
static uint8_t icert_root_fingerprint[SHA256_DIGEST_SIZE];

/** Root of trust for iPhone certificates */
static struct x509_root icert_root = {
        .refcnt = REF_INIT ( ref_no_free ),
        .digest = &sha256_algorithm,
        .count = 1,
        .fingerprints = icert_root_fingerprint,
};

/** Single zero byte used in constructed certificates */
static const uint8_t icert_nul[] = { 0x00 };

/** "RSA algorithm" identifier used in constructed certificates */
static const uint8_t icert_rsa[] = {
        /* algorithm */
        ASN1_SHORT ( ASN1_SEQUENCE,
                     ASN1_SHORT ( ASN1_OID, ASN1_OID_RSAENCRYPTION ),
                     ASN1_NULL, 0x00 )
};

/** "SHA-256 with RSA algorithm" identifier used in constructed certificates */
static const uint8_t icert_sha256_rsa[] = {
        ASN1_SHORT ( ASN1_SEQUENCE,
                     ASN1_SHORT ( ASN1_OID, ASN1_OID_SHA256WITHRSAENCRYPTION ),
                     ASN1_NULL, 0x00 ),
};

/** Extensions used in constructed root certificate */
static const uint8_t icert_root_exts_data[] = {
        /* extensions */
        ASN1_SHORT ( ASN1_EXPLICIT_TAG ( 3 ), ASN1_SHORT ( ASN1_SEQUENCE,
        /* basicConstraints */
        ASN1_SHORT ( ASN1_SEQUENCE,
                     /* extnID */
                     ASN1_SHORT ( ASN1_OID, ASN1_OID_BASICCONSTRAINTS ),
                     /* critical */
                     ASN1_SHORT ( ASN1_BOOLEAN, 0xff ),
                     /* extnValue */
                     ASN1_SHORT ( ASN1_OCTET_STRING,
                                  ASN1_SHORT ( ASN1_SEQUENCE,
                                               ASN1_SHORT ( ASN1_BOOLEAN,
                                                            0xff ) ) ) ) ) )
};

/** Extensions used in constructed root certificate */
static struct asn1_cursor icert_root_exts =
        ASN1_CURSOR ( icert_root_exts_data );

/** Extensions used in constructed leaf certificates */
static const uint8_t icert_leaf_exts_data[] = {
        /* extensions */
        ASN1_SHORT ( ASN1_EXPLICIT_TAG ( 3 ), ASN1_SHORT ( ASN1_SEQUENCE,
        /* basicConstraints */
        ASN1_SHORT ( ASN1_SEQUENCE,
                     /* extnID */
                     ASN1_SHORT ( ASN1_OID, ASN1_OID_BASICCONSTRAINTS ),
                     /* critical */
                     ASN1_SHORT ( ASN1_BOOLEAN, 0xff ),
                     /* extnValue */
                     ASN1_SHORT ( ASN1_OCTET_STRING,
                                  ASN1_SHORT ( ASN1_SEQUENCE,
                                               ASN1_SHORT ( ASN1_BOOLEAN,
                                                            0x00 ) ) ) ),
        /* keyUsage */
        ASN1_SHORT ( ASN1_SEQUENCE,
                     /* extnID */
                     ASN1_SHORT ( ASN1_OID, ASN1_OID_KEYUSAGE ),
                     /* critical */
                     ASN1_SHORT ( ASN1_BOOLEAN, 0xff ),
                     /* extnValue */
                     ASN1_SHORT ( ASN1_OCTET_STRING,
                                  ASN1_SHORT ( ASN1_BIT_STRING, 0x07,
                                               ( X509_DIGITAL_SIGNATURE |
                                                 X509_KEY_ENCIPHERMENT ),
                                               0x00 ) ) ) ) )
};

/** Extensions used in constructed leaf certificates */
static struct asn1_cursor icert_leaf_exts =
        ASN1_CURSOR ( icert_leaf_exts_data );

/** "TBSCertificate" prefix in constructed certificates */
static const uint8_t icert_tbs_prefix[] = {
        /* version */
        ASN1_SHORT ( ASN1_EXPLICIT_TAG ( 0 ), ASN1_SHORT ( ASN1_INTEGER, 2 ) ),
        /* serialNumber */
        ASN1_SHORT ( ASN1_INTEGER, 0 ),
        /* signature */
        ASN1_SHORT ( ASN1_SEQUENCE,
                     ASN1_SHORT ( ASN1_OID, ASN1_OID_SHA256WITHRSAENCRYPTION ),
                     ASN1_NULL, 0x00 )
};

/** Validity period in constructed certificates */
static const uint8_t icert_validity[] = {
        /* validity */
        ASN1_SHORT ( ASN1_SEQUENCE,
                     /* notBefore */
                     ASN1_SHORT ( ASN1_GENERALIZED_TIME,
                                  '1', '9', '7', '8', '1', '2', '1', '0',
                                  '2', '2', '0', '0', '0', '0', 'Z' ),
                     /* notAfter */
                     ASN1_SHORT ( ASN1_GENERALIZED_TIME,
                                  '2', '9', '9', '9', '0', '1', '0', '1',
                                  '0', '0', '0', '0', '0', '0', 'Z' ) )
};

/** "Root" subject name */
static const uint8_t icert_name_root_data[] = {
        ASN1_SHORT ( ASN1_SEQUENCE, ASN1_SHORT ( ASN1_SET,
        ASN1_SHORT ( ASN1_SEQUENCE,
                     ASN1_SHORT ( ASN1_OID, ASN1_OID_COMMON_NAME ),
                     ASN1_SHORT ( ASN1_UTF8_STRING, 'R', 'o', 'o', 't' ) ) ) )
};

/** "Root" subject name */
static struct asn1_cursor icert_name_root =
        ASN1_CURSOR ( icert_name_root_data );

/** "iPXE" subject name */
static const uint8_t icert_name_ipxe_data[] = {
        ASN1_SHORT ( ASN1_SEQUENCE, ASN1_SHORT ( ASN1_SET,
        ASN1_SHORT ( ASN1_SEQUENCE,
                     ASN1_SHORT ( ASN1_OID, ASN1_OID_COMMON_NAME ),
                     ASN1_SHORT ( ASN1_UTF8_STRING, 'i', 'P', 'X', 'E' ) ) ) )
};

/** "iPXE" subject name */
static struct asn1_cursor icert_name_ipxe =
        ASN1_CURSOR ( icert_name_ipxe_data );

/** "iPhone" subject name */
static const uint8_t icert_name_iphone_data[] = {
        ASN1_SHORT ( ASN1_SEQUENCE, ASN1_SHORT ( ASN1_SET,
        ASN1_SHORT ( ASN1_SEQUENCE,
                     ASN1_SHORT ( ASN1_OID, ASN1_OID_COMMON_NAME ),
                     ASN1_SHORT ( ASN1_UTF8_STRING,
                                  'i', 'P', 'h', 'o', 'n', 'e' ) ) ) )
};

/** "iPhone" subject name */
static struct asn1_cursor icert_name_iphone =
        ASN1_CURSOR ( icert_name_iphone_data );

/** Public key(s) used for pairing */
static const uint8_t icert_public_a[] __unused = {
        0x02, 0x81, 0x81, 0x00, 0xc9, 0xc0, 0xdd, 0xa6, 0xd5, 0xf9, 0x05, 0x3e,
        0x1d, 0xcb, 0x67, 0x08, 0xa8, 0x50, 0x27, 0x63, 0x95, 0x87, 0x42, 0x7e,
        0xfb, 0xff, 0x55, 0x55, 0xb8, 0xc0, 0x6f, 0x13, 0xcb, 0xf7, 0xc5, 0x1b,
        0xda, 0x44, 0x3c, 0xbc, 0x1a, 0xe1, 0x15, 0x1e, 0xab, 0x56, 0x74, 0x02,
        0x8b, 0xb3, 0xcd, 0x42, 0x56, 0xcd, 0x9c, 0xc3, 0x15, 0xe2, 0x33, 0x97,
        0x6d, 0x77, 0xdd, 0x20, 0x3a, 0x74, 0xb1, 0x4c, 0xee, 0xeb, 0xe8, 0xaa,
        0x20, 0x71, 0x5a, 0xa2, 0x5b, 0xf8, 0x1a, 0xcb, 0xd2, 0x7b, 0x96, 0xb6,
        0x42, 0xb4, 0x7c, 0x7a, 0x13, 0xec, 0x55, 0xd3, 0x36, 0x8b, 0xe3, 0x17,
        0xc5, 0xc4, 0xcc, 0xe0, 0x27, 0x8c, 0xed, 0xa1, 0x4c, 0x8a, 0x50, 0x4a,
        0x1c, 0xc4, 0x58, 0xf6, 0xcd, 0xcc, 0xc3, 0x5f, 0xe6, 0x3c, 0xff, 0x97,
        0x51, 0xed, 0xf5, 0xaa, 0x89, 0xcc, 0x3f, 0x63, 0x67, 0x46, 0x9f, 0xbf,
        0x02, 0x03, 0x01, 0x00, 0x01
};
static const uint8_t icert_public_b[] __unused = {
        0x02, 0x81, 0x81, 0x00, 0xcd, 0x96, 0x81, 0x78, 0xbb, 0x2e, 0x64, 0xda,
        0xd3, 0x7e, 0xd7, 0x3a, 0xac, 0x3f, 0x00, 0xe5, 0x41, 0x65, 0x56, 0xac,
        0x2d, 0x77, 0xc0, 0x1a, 0xad, 0x32, 0xca, 0x0c, 0x72, 0xae, 0xdb, 0x57,
        0xc1, 0xc7, 0x79, 0xef, 0xc6, 0x71, 0x9f, 0xad, 0x82, 0x14, 0x94, 0x4b,
        0xf9, 0xd8, 0x78, 0xf1, 0xca, 0x99, 0xf5, 0x71, 0x07, 0x88, 0xd7, 0x55,
        0xc7, 0xcb, 0x36, 0x5d, 0xdb, 0x84, 0x46, 0xac, 0x05, 0xea, 0xf1, 0xe1,
        0xbe, 0x91, 0x50, 0x85, 0x1e, 0x64, 0xab, 0x02, 0x82, 0xab, 0xba, 0x42,
        0x06, 0x5a, 0xe3, 0xc3, 0x25, 0xd0, 0x95, 0x04, 0x54, 0xb4, 0x44, 0x40,
        0x5a, 0x42, 0x06, 0x04, 0x7d, 0x3b, 0x9e, 0xaf, 0x2e, 0xe9, 0xc8, 0xad,
        0x46, 0x3a, 0xff, 0xe2, 0x39, 0xc8, 0x48, 0x0a, 0x49, 0xaa, 0xfe, 0x1f,
        0x6c, 0x91, 0x5d, 0x1d, 0xd6, 0xb0, 0x04, 0xd1, 0x6c, 0xb2, 0x43, 0xaf,
        0x02, 0x03, 0x01, 0x00, 0x01
};

/**
 * "Private" key(s) used for pairing
 *
 * Yes, this publicly visible "private" key completely obviates any
 * nominal security provided by the pairing process.  Looked at
 * another way, this modifies the iPhone to behave like every other
 * USB tethering device: if the cable is physically connected and
 * tethering is enabled then the device will Just Work.
 *
 * Unlike Android, the iPhone seems to have no meaningful permissions
 * model: any device that is trusted to use the phone for tethering
 * seems to also be trusted to use the iPhone for any other purpose
 * (e.g. accessing files, reading messages, etc).  Apple should
 * probably fix this at some point, e.g. via defining extended key
 * usages in the root and host certificates.
 */
static const uint8_t icert_private_a[] __unused = {
        0x02, 0x81, 0x80, 0x1d, 0x60, 0xb7, 0x25, 0xdf, 0x0c, 0x76, 0xc5, 0xf7,
        0xc2, 0xb1, 0x8b, 0x22, 0x2f, 0x21, 0xbd, 0x2f, 0x7d, 0xd5, 0xa1, 0xf6,
        0x01, 0xd5, 0x24, 0x39, 0x55, 0xd4, 0x16, 0xd6, 0xe1, 0x8a, 0x53, 0x26,
        0xf2, 0x3e, 0xc1, 0xc9, 0x4c, 0x33, 0x2e, 0x17, 0x16, 0xec, 0xa7, 0x9e,
        0x3e, 0x1d, 0x4a, 0x66, 0xa7, 0x64, 0x07, 0x48, 0x3d, 0x7a, 0xf3, 0xb6,
        0xdd, 0xf8, 0x56, 0x04, 0x0d, 0x0f, 0xef, 0xf8, 0xbd, 0xbc, 0x73, 0xe2,
        0xc2, 0xae, 0x1b, 0x87, 0x90, 0x18, 0x2a, 0x68, 0xff, 0xae, 0x49, 0xdf,
        0x7c, 0xff, 0xe8, 0x44, 0xa8, 0x3e, 0x4e, 0x4f, 0xf5, 0xfa, 0x51, 0x96,
        0xb8, 0x08, 0xf3, 0x18, 0xd6, 0x52, 0xdf, 0x3a, 0x8a, 0xed, 0xda, 0xcd,
        0xb4, 0x06, 0x99, 0x41, 0xcb, 0x23, 0x17, 0xaf, 0xc3, 0x3e, 0xfe, 0xdf,
        0x97, 0xf3, 0xd6, 0x18, 0x7e, 0x03, 0xaf, 0x62, 0xb2, 0xc8, 0xc9
};
static const uint8_t icert_private_b[] __unused = {
        0x02, 0x81, 0x80, 0x45, 0xbd, 0xc0, 0xbe, 0x0c, 0x01, 0x79, 0x05, 0x22,
        0xa9, 0xec, 0xa9, 0x62, 0xb5, 0x1c, 0xc0, 0xa8, 0xa6, 0x8f, 0xf8, 0x68,
        0x94, 0x2e, 0xfe, 0xdd, 0xb2, 0x55, 0x08, 0x53, 0xff, 0x2d, 0x39, 0x5f,
        0xeb, 0x23, 0x5a, 0x4b, 0x9f, 0x4f, 0xe3, 0xb4, 0x34, 0xf6, 0xf9, 0xaf,
        0x0f, 0xd8, 0x37, 0x6d, 0xdb, 0x3c, 0x7f, 0xd3, 0x66, 0x80, 0x66, 0x01,
        0x18, 0xd6, 0xa0, 0x90, 0x4f, 0x17, 0x09, 0xb8, 0x68, 0x44, 0xf0, 0xde,
        0x16, 0x4a, 0x8a, 0x0d, 0xa7, 0x5f, 0xb5, 0x4c, 0x53, 0xcc, 0x21, 0xdd,
        0x4f, 0x05, 0x64, 0xa5, 0xc5, 0xac, 0x2c, 0xd8, 0x0a, 0x7b, 0xf5, 0xa4,
        0x63, 0x32, 0xb0, 0x2c, 0xf8, 0xef, 0x8c, 0xf8, 0x2c, 0xba, 0x1c, 0x2c,
        0xc7, 0x0a, 0xf3, 0xe9, 0x8f, 0xfb, 0x0a, 0x61, 0x1b, 0x3a, 0xdd, 0x9f,
        0x74, 0x7d, 0xb3, 0x42, 0x59, 0x52, 0x07, 0x59, 0x8e, 0xb7, 0x41
};

/** Key pair selection
 *
 * This exists only to allow for testing of the process for handling a
 * failed TLS negotiation.
 */
#define icert_key_suffix a
#define icert_key_variable( prefix ) _C2 ( prefix, icert_key_suffix )
#define icert_public icert_key_variable ( icert_public_ )
#define icert_private icert_key_variable ( icert_private_ )

/** PEM certificate prefix */
static const char icert_begin[] = "-----BEGIN CERTIFICATE-----\n";

/** PEM certificate suffix */
static const char icert_end[] = "\n-----END CERTIFICATE-----\n";

/**
 * Free pairing certificates
 *
 * @v icert             Pairing certificates
 */
static void icert_free ( struct icert *icert ) {

        privkey_put ( icert->key );
        x509_put ( icert->root );
        x509_put ( icert->host );
        x509_put ( icert->device );
        memset ( icert, 0, sizeof ( *icert ) );
}

/**
 * Construct certificate
 *
 * @v icert             Pairing certificates
 * @v subject           Subject name
 * @v issuer            Issuer name
 * @v private           Private key
 * @v public            Public key
 * @v exts              Certificate extensions
 * @v cert              Certificate to fill in
 * @ret rc              Return status code
 *
 * On success, the caller is responsible for eventually calling
 * x509_put() on the allocated encoded certificate.
 */
static int icert_cert ( struct icert *icert, struct asn1_cursor *subject,
                        struct asn1_cursor *issuer, struct asn1_cursor *private,
                        struct asn1_cursor *public, struct asn1_cursor *exts,
                        struct x509_certificate **cert ) {
        struct digest_algorithm *digest = &sha256_algorithm;
        struct pubkey_algorithm *pubkey = &rsa_algorithm;
        struct asn1_builder spki = { NULL, 0 };
        struct asn1_builder tbs = { NULL, 0 };
        struct asn1_builder raw = { NULL, 0 };
        uint8_t digest_ctx[SHA256_CTX_SIZE];
        uint8_t digest_out[SHA256_DIGEST_SIZE];
        int rc;

        /* Construct subjectPublicKeyInfo */
        if ( ( rc = ( asn1_prepend_raw ( &spki, public->data, public->len ),
                      asn1_prepend_raw ( &spki, icert_nul,
                                         sizeof ( icert_nul ) ),
                      asn1_wrap ( &spki, ASN1_BIT_STRING ),
                      asn1_prepend_raw ( &spki, icert_rsa,
                                         sizeof ( icert_rsa ) ),
                      asn1_wrap ( &spki, ASN1_SEQUENCE ) ) ) != 0 ) {
                DBGC ( icert, "ICERT %p could not build subjectPublicKeyInfo: "
                       "%s\n", icert, strerror ( rc ) );
                goto err_spki;
        }

        /* Construct tbsCertificate */
        if ( ( rc = ( asn1_prepend_raw ( &tbs, exts->data, exts->len ),
                      asn1_prepend_raw ( &tbs, spki.data, spki.len ),
                      asn1_prepend_raw ( &tbs, subject->data, subject->len ),
                      asn1_prepend_raw ( &tbs, icert_validity,
                                         sizeof ( icert_validity ) ),
                      asn1_prepend_raw ( &tbs, issuer->data, issuer->len ),
                      asn1_prepend_raw ( &tbs, icert_tbs_prefix,
                                         sizeof ( icert_tbs_prefix ) ),
                      asn1_wrap ( &tbs, ASN1_SEQUENCE ) ) ) != 0 ) {
                DBGC ( icert, "ICERT %p could not build tbsCertificate: %s\n",
                       icert, strerror ( rc ) );
                goto err_tbs;
        }

        /* Calculate certificate digest */
        digest_init ( digest, digest_ctx );
        digest_update ( digest, digest_ctx, tbs.data, tbs.len );
        digest_final ( digest, digest_ctx, digest_out );

        /* Construct signature using "private" key */
        if ( ( rc = pubkey_sign ( pubkey, private, digest, digest_out,
                                  &raw ) ) != 0 ) {
                DBGC ( icert, "ICERT %p could not sign: %s\n",
                       icert, strerror ( rc ) );
                goto err_pubkey_sign;
        }

        /* Construct raw certificate data */
        if ( ( rc = ( asn1_prepend_raw ( &raw, icert_nul,
                                         sizeof ( icert_nul ) ),
                      asn1_wrap ( &raw, ASN1_BIT_STRING ),
                      asn1_prepend_raw ( &raw, icert_sha256_rsa,
                                         sizeof ( icert_sha256_rsa ) ),
                      asn1_prepend_raw ( &raw, tbs.data, tbs.len ),
                      asn1_wrap ( &raw, ASN1_SEQUENCE ) ) ) != 0 ) {
                DBGC ( icert, "ICERT %p could not build certificate: %s\n",
                       icert, strerror ( rc ) );
                goto err_raw;
        }

        /* Parse certificate */
        if ( ( rc = x509_certificate ( raw.data, raw.len, cert ) ) != 0 ) {
                DBGC ( icert, "ICERT %p invalid certificate: %s\n",
                       icert, strerror ( rc ) );
                DBGC_HDA ( icert, 0, raw.data, raw.len );
                goto err_x509;
        }

 err_x509:
 err_raw:
 err_pubkey_sign:
 err_tbs:
 err_spki:
        free ( raw.data );
        free ( tbs.data );
        free ( spki.data );
        return rc;
}

/**
 * Construct certificates
 *
 * @v icert             Certificate set
 * @v pubkey            Device public key
 * @ret rc              Return status code
 */
static int icert_certs ( struct icert *icert, struct asn1_cursor *key ) {
        struct digest_algorithm *digest = icert_root.digest;
        struct asn1_builder public = { NULL, 0 };
        struct asn1_builder *private;
        int rc;

        /* Free any existing key and certificates */
        icert_free ( icert );

        /* Allocate "private" key */
        icert->key = zalloc ( sizeof ( *icert->key ) );
        if ( ! icert->key ) {
                rc = -ENOMEM;
                goto error;
        }
        privkey_init ( icert->key );
        private = &icert->key->builder;

        /* Construct our "private" key */
        if ( ( rc = ( asn1_prepend_raw ( private, icert_private,
                                         sizeof ( icert_private ) ),
                      asn1_prepend_raw ( private, icert_public,
                                         sizeof ( icert_public ) ),
                      asn1_prepend ( private, ASN1_INTEGER, icert_nul,
                                     sizeof ( icert_nul ) ),
                      asn1_wrap ( private, ASN1_SEQUENCE ) ) ) != 0 ) {
                DBGC ( icert, "ICERT %p could not build private key: %s\n",
                       icert, strerror ( rc ) );
                goto error;
        }

        /* Construct our own public key */
        if ( ( rc = ( asn1_prepend_raw ( &public, icert_public,
                                         sizeof ( icert_public ) ),
                      asn1_wrap ( &public, ASN1_SEQUENCE ) ) ) != 0 ) {
                DBGC ( icert, "ICERT %p could not build public key: %s\n",
                       icert, strerror ( rc ) );
                goto error;
        }

        /* Construct root certificate */
        if ( ( rc = icert_cert ( icert, &icert_name_root, &icert_name_root,
                                 asn1_built ( private ), asn1_built ( &public ),
                                 &icert_root_exts, &icert->root ) ) != 0 )
                goto error;

        /* Construct host certificate */
        if ( ( rc = icert_cert ( icert, &icert_name_ipxe, &icert_name_root,
                                 asn1_built ( private ), asn1_built ( &public ),
                                 &icert_leaf_exts, &icert->host ) ) != 0 )
                goto error;

        /* Construct device certificate */
        if ( ( rc = icert_cert ( icert, &icert_name_iphone, &icert_name_root,
                                 asn1_built ( private ), key,
                                 &icert_leaf_exts, &icert->device ) ) != 0 )
                goto error;

        /* Construct root of trust */
        assert ( digest->digestsize == sizeof ( icert_root_fingerprint ) );
        x509_fingerprint ( icert->root, digest, icert_root_fingerprint );

        /* Free constructed keys */
        free ( public.data );
        return 0;

 error:
        icert_free ( icert );
        free ( public.data );
        return rc;
}

/**
 * Construct doubly base64-encoded certificate
 *
 * @v icert             Pairing certificates
 * @v cert              X.509 certificate
 * @v encenc            Doubly base64-encoded certificate to construct
 * @ret rc              Return status code
 *
 * On success, the caller is responsible for eventually calling free()
 * on the allocated doubly encoded encoded certificate.
 */
static int icert_encode ( struct icert *icert, struct x509_certificate *cert,
                          char **encenc ) {
        size_t encencoded_len;
        size_t encoded_len;
        size_t pem_len;
        char *pem;
        int rc;

        /* Sanity check */
        assert ( cert != NULL );

        /* Create PEM */
        encoded_len = ( base64_encoded_len ( cert->raw.len ) + 1 /* NUL */ );
        pem_len = ( ( sizeof ( icert_begin ) - 1 /* NUL */ ) +
                    ( encoded_len - 1 /* NUL */ ) +
                    ( sizeof ( icert_end ) - 1 /* NUL */ ) +
                    1 /* NUL */ );
        pem = malloc ( pem_len );
        if ( ! pem ) {
                rc = -ENOMEM;
                goto err_alloc_pem;
        }
        strcpy ( pem, icert_begin );
        base64_encode ( cert->raw.data, cert->raw.len,
                        ( pem + sizeof ( icert_begin ) - 1 /* NUL */ ),
                        encoded_len );
        strcpy ( ( pem +
                   ( sizeof ( icert_begin ) - 1 /* NUL */ ) +
                   ( encoded_len - 1 /* NUL */ ) ), icert_end );
        DBGC2 ( icert, "ICERT %p \"%s\" certificate:\n%s",
                icert, x509_name ( cert ), pem );

        /* Base64-encode the PEM (sic) */
        encencoded_len = ( base64_encoded_len ( pem_len - 1 /* NUL */ )
                           + 1 /* NUL */ );
        *encenc = malloc ( encencoded_len );
        if ( ! *encenc ) {
                rc = -ENOMEM;
                goto err_alloc_encenc;
        }
        base64_encode ( pem, ( pem_len - 1 /* NUL */ ), *encenc,
                        encencoded_len );

        /* Success */
        rc = 0;

 err_alloc_encenc:
        free ( pem );
 err_alloc_pem:
        return rc;
}

/******************************************************************************
 *
 * iPhone USB multiplexer
 *
 ******************************************************************************
 *
 * The iPhone USB multiplexer speaks a protocol that is almost, but
 * not quite, entirely unlike TCP.
 *
 */

/**
 * Transmit message
 *
 * @v imux              USB multiplexer
 * @v iobuf             I/O buffer
 * @ret rc              Return status code
 */
static int imux_tx ( struct imux *imux, struct io_buffer *iobuf ) {
        struct imux_header *hdr = iobuf->data;
        size_t len = iob_len ( iobuf );
        int rc;

        /* Populate header */
        assert ( len >= sizeof ( *hdr ) );
        hdr->len = htonl ( len );
        hdr->in_seq = htons ( imux->in_seq );
        hdr->out_seq = htons ( imux->out_seq );
        DBGCP ( imux, "IMUX %p transmitting:\n", imux );
        DBGCP_HDA ( imux, 0, hdr, len );

        /* Transmit message */
        if ( ( rc = usb_stream ( &imux->usbnet.out, iobuf, 1 ) ) != 0 )
                goto err;

        /* Increment sequence number */
        imux->out_seq++;

        return 0;

 err:
        free_iob ( iobuf );
        return rc;
}

/**
 * Transmit version message
 *
 * @v imux              USB multiplexer
 * @ret rc              Return status code
 */
static int imux_tx_version ( struct imux *imux ) {
        struct io_buffer *iobuf;
        struct imux_header_version *vers;
        int rc;

        /* Allocate I/O buffer */
        iobuf = alloc_iob ( sizeof ( *vers ) );
        if ( ! iobuf )
                return -ENOMEM;
        vers = iob_put ( iobuf, sizeof ( *vers ) );

        /* Construct version message */
        memset ( vers, 0, sizeof ( *vers ) );
        vers->hdr.protocol = htonl ( IMUX_VERSION );

        /* Transmit message */
        if ( ( rc = imux_tx ( imux, iob_disown ( iobuf ) ) ) != 0 )
                return rc;

        return 0;
}

/**
 * Transmit pseudo-TCP message
 *
 * @v imux              USB multiplexer
 * @v iobuf             I/O buffer
 * @ret rc              Return status code
 */
static int imux_tx_tcp ( struct imux *imux, struct io_buffer *iobuf ) {
        struct imux_header_tcp *tcp = iobuf->data;
        size_t len = iob_len ( iobuf );
        int rc;

        /* Populate TCP header */
        assert ( len >= sizeof ( *tcp ) );
        tcp->hdr.protocol = htonl ( IMUX_TCP );
        tcp->tcp.src = htons ( imux->port );
        tcp->tcp.dest = htons ( IMUX_PORT_LOCKDOWND );
        tcp->tcp.seq = htonl ( imux->tcp_seq );
        tcp->tcp.ack = htonl ( imux->tcp_ack );
        tcp->tcp.hlen = ( ( sizeof ( tcp->tcp ) / 4 ) << 4 );
        tcp->tcp.win = htons ( IMUX_WINDOW );

        /* Transmit message */
        if ( ( rc = imux_tx ( imux, iob_disown ( iobuf ) ) ) != 0 )
                return rc;

        /* Update TCP sequence */
        imux->tcp_seq += ( len - sizeof ( *tcp ) );

        return 0;
}

/**
 * Transmit pseudo-TCP SYN
 *
 * @v imux              USB multiplexer
 * @ret rc              Return status code
 */
static int imux_tx_syn ( struct imux *imux ) {
        struct io_buffer *iobuf;
        struct imux_header_tcp *syn;
        int rc;

        /* Allocate I/O buffer */
        iobuf = alloc_iob ( sizeof ( *syn ) );
        if ( ! iobuf )
                return -ENOMEM;
        syn = iob_put ( iobuf, sizeof ( *syn ) );

        /* Construct TCP SYN message */
        memset ( syn, 0, sizeof ( *syn ) );
        syn->tcp.flags = TCP_SYN;

        /* Transmit message */
        if ( ( rc = imux_tx_tcp ( imux, iob_disown ( iobuf ) ) ) != 0 )
                return rc;

        /* Increment TCP sequence to compensate for SYN */
        imux->tcp_seq++;

        return 0;
}

/**
 * Open pairing client
 *
 * @v imux              USB multiplexer
 * @ret rc              Return status code
 */
static int imux_start_pair ( struct imux *imux ) {
        int rc;

        /* Disconnect any existing pairing client */
        intf_restart ( &imux->tcp, -EPIPE );

        /* Create pairing client */
        if ( ( rc = ipair_create ( &imux->tcp, imux->flags ) ) != 0 )
                return rc;

        return 0;
}

/**
 * Receive version message
 *
 * @v imux              USB multiplexer
 */
static void imux_rx_version ( struct imux *imux ) {

        /* Reset output sequence */
        imux->out_seq = 0;

        /* Send TCP SYN */
        imux->action = imux_tx_syn;
}

/**
 * Receive log message
 *
 * @v imux              USB multiplexer
 * @v hdr               Message header
 * @v len               Length of message
 */
static void imux_rx_log ( struct imux *imux, struct imux_header *hdr,
                          size_t len ) {
        struct imux_header_log *log =
                container_of ( hdr, struct imux_header_log, hdr );
        unsigned int level;
        size_t msg_len;
        char *tmp;

        /* Sanity check */
        if ( len < sizeof ( *log ) ) {
                DBGC ( imux, "IMUX %p malformed log message:\n", imux );
                DBGC_HDA ( imux, 0, log, len );
                return;
        }

        /* First byte is the log level, followed by a printable
         * message with no NUL terminator.  Extract the log level,
         * then shuffle the message down within the buffer and append
         * a NUL terminator.
         */
        msg_len = ( len - sizeof ( *hdr ) );
        level = log->level;
        tmp = ( ( void * ) &log->level );
        memmove ( tmp, &log->msg, msg_len );
        tmp[msg_len] = '\0';

        /* Print log message */
        DBGC ( imux, "IMUX %p <%d>: %s\n", imux, level, tmp );
}

/**
 * Receive pseudo-TCP SYN+ACK
 *
 * @v imux              USB multiplexer
 */
static void imux_rx_syn ( struct imux *imux ) {

        /* Increment TCP acknowledgement to compensate for SYN */
        imux->tcp_ack++;

        /* Start pairing client */
        imux->action = imux_start_pair;
}

/**
 * Receive pseudo-TCP message
 *
 * @v imux              USB multiplexer
 * @v iobuf             I/O buffer
 */
static void imux_rx_tcp ( struct imux *imux, struct io_buffer *iobuf ) {
        struct imux_header_tcp *tcp = iobuf->data;
        size_t len = iob_len ( iobuf );
        int rc;

        /* Sanity check */
        if ( len < sizeof ( *tcp ) ) {
                DBGC ( imux, "IMUX %p malformed TCP message:\n", imux );
                DBGC_HDA ( imux, 0, tcp, len );
                goto error;
        }

        /* Ignore unexpected packets */
        if ( tcp->tcp.dest != htons ( imux->port ) ) {
                DBGC ( imux, "IMUX %p ignoring unexpected TCP port %d:\n",
                       imux, ntohs ( tcp->tcp.dest ) );
                DBGC_HDA ( imux, 0, tcp, len );
                goto error;
        }

        /* Ignore resets */
        if ( tcp->tcp.flags & TCP_RST ) {
                DBGC ( imux, "IMUX %p ignoring TCP RST\n", imux );
                DBGC2_HDA ( imux, 0, tcp, len );
                goto error;
        }

        /* Record ACK number */
        imux->tcp_ack = ( ntohl ( tcp->tcp.seq ) + len - sizeof ( *tcp ) );

        /* Handle received message */
        if ( tcp->tcp.flags & TCP_SYN ) {

                /* Received SYN+ACK */
                imux_rx_syn ( imux );

        } else {

                /* Strip header */
                iob_pull ( iobuf, sizeof ( *tcp ) );

                /* Deliver via socket */
                if ( ( rc = xfer_deliver_iob ( &imux->tcp,
                                               iob_disown ( iobuf ) ) ) != 0 )
                        goto error;
        }

 error:
        free_iob ( iobuf );
}

/**
 * Complete bulk IN transfer
 *
 * @v ep                USB endpoint
 * @v iobuf             I/O buffer
 * @v rc                Completion status code
 */
static void imux_in_complete ( struct usb_endpoint *ep,
                               struct io_buffer *iobuf, int rc ) {
        struct imux *imux = container_of ( ep, struct imux, usbnet.in );
        struct imux_header *hdr = iobuf->data;
        size_t len = iob_len ( iobuf );

        /* Ignore packets cancelled when the endpoint closes */
        if ( ! ep->open )
                goto drop;

        /* Report USB errors */
        if ( rc != 0 ) {
                DBGC ( imux, "IMUX %p bulk IN failed: %s\n",
                       imux, strerror ( rc ) );
                goto drop;
        }

        /* Sanity check */
        if ( len < sizeof ( *hdr ) ) {
                DBGC ( imux, "IMUX %p malformed message:\n", imux );
                DBGC_HDA ( imux, 0, hdr, len );
                goto drop;
        }

        /* Record input sequence */
        imux->in_seq = ntohs ( hdr->in_seq );

        /* Handle according to protocol */
        DBGCP ( imux, "IMUX %p received:\n", imux );
        DBGCP_HDA ( imux, 0, hdr, len );
        switch ( hdr->protocol ) {
        case htonl ( IMUX_VERSION ):
                imux_rx_version ( imux );
                break;
        case htonl ( IMUX_LOG ):
                imux_rx_log ( imux, hdr, len );
                break;
        case htonl ( IMUX_TCP ):
                imux_rx_tcp ( imux, iob_disown ( iobuf ) );
                break;
        default:
                DBGC ( imux, "IMUX %p unknown message type %d:\n",
                       imux, ntohl ( hdr->protocol ) );
                DBGC_HDA ( imux, 0, hdr, len );
                break;
        }

 drop:
        free_iob ( iobuf );
}

/** Bulk IN endpoint operations */
static struct usb_endpoint_driver_operations imux_in_operations = {
        .complete = imux_in_complete,
};

/**
 * Complete bulk OUT transfer
 *
 * @v ep                USB endpoint
 * @v iobuf             I/O buffer
 * @v rc                Completion status code
 */
static void imux_out_complete ( struct usb_endpoint *ep,
                                struct io_buffer *iobuf, int rc ) {
        struct imux *imux = container_of ( ep, struct imux, usbnet.out );

        /* Report USB errors */
        if ( rc != 0 ) {
                DBGC ( imux, "IMUX %p bulk OUT failed: %s\n",
                       imux, strerror ( rc ) );
                goto error;
        }

 error:
        free_iob ( iobuf );
}

/** Bulk OUT endpoint operations */
static struct usb_endpoint_driver_operations imux_out_operations = {
        .complete = imux_out_complete,
};

/**
 * Shut down USB multiplexer
 *
 * @v imux              USB multiplexer
 */
static void imux_shutdown ( struct imux *imux ) {

        /* Shut down interfaces */
        intf_shutdown ( &imux->tcp, -ECANCELED );

        /* Close USB network device, if open */
        if ( process_running ( &imux->process ) ) {
                process_del ( &imux->process );
                usbnet_close ( &imux->usbnet );
        }
}

/**
 * Close USB multiplexer
 *
 * @v imux              USB multiplexer
 * @v rc                Reason for close
 */
static void imux_close ( struct imux *imux, int rc ) {
        struct iphone *iphone;

        /* Restart interfaces */
        intf_restart ( &imux->tcp, rc );

        /* Record pairing status */
        imux->rc = rc;

        /* Trigger link check on any associated iPhones */
        list_for_each_entry ( iphone, &iphones, list ) {
                if ( iphone->usb == imux->usb )
                        start_timer_nodelay ( &iphone->timer );
        }

        /* Retry pairing on any error */
        if ( rc != 0 ) {

                /* Increment port number */
                imux->port++;

                /* Request pairing on any retry attempt */
                imux->flags = IPAIR_REQUEST;

                /* Send new pseudo-TCP SYN */
                imux->action = imux_tx_syn;

                DBGC ( imux, "IMUX %p retrying pairing: %s\n",
                       imux, strerror ( rc ) );
                return;
        }

        /* Shut down multiplexer on pairing success */
        imux_shutdown ( imux );
}

/**
 * Allocate I/O buffer for pseudo-TCP socket
 *
 * @v imux              USB multiplexer
 * @v len               I/O buffer payload length
 * @ret iobuf           I/O buffer
 */
static struct io_buffer * imux_alloc_iob ( struct imux *imux __unused,
                                           size_t len ) {
        struct imux_header_tcp *tcp;
        struct io_buffer *iobuf;

        /* Allocate I/O buffer */
        iobuf = alloc_iob ( sizeof ( *tcp ) + len );
        if ( ! iobuf )
                return NULL;

        /* Reserve space for pseudo-TCP message header */
        iob_reserve ( iobuf, sizeof ( *tcp ) );

        return iobuf;
}

/**
 * Transmit packet via pseudo-TCP socket
 *
 * @v imux              USB multiplexer
 * @v iobuf             I/O buffer
 * @v meta              Data transfer metadata
 * @ret rc              Return status code
 */
static int imux_deliver ( struct imux *imux, struct io_buffer *iobuf,
                          struct xfer_metadata *meta __unused ) {
        struct imux_header_tcp *tcp;

        /* Prepend pseudo-TCP header */
        tcp = iob_push ( iobuf, sizeof ( *tcp ) );
        memset ( tcp, 0, sizeof ( *tcp ) );
        tcp->tcp.flags = TCP_ACK;

        /* Transmit pseudo-TCP packet */
        return imux_tx_tcp ( imux, iob_disown ( iobuf ) );
}

/** Pseudo-TCP socket interface operations */
static struct interface_operation imux_tcp_operations[] = {
        INTF_OP ( xfer_deliver, struct imux *, imux_deliver ),
        INTF_OP ( xfer_alloc_iob, struct imux *, imux_alloc_iob ),
        INTF_OP ( intf_close, struct imux *, imux_close ),
};

/** Pseudo-TCP socket interface descriptor */
static struct interface_descriptor imux_tcp_desc =
        INTF_DESC ( struct imux, tcp, imux_tcp_operations );

/**
 * Multiplexer process
 *
 * @v imux              USB multiplexer
 */
static void imux_step ( struct imux *imux ) {
        int rc;

        /* Poll USB bus */
        usb_poll ( imux->bus );

        /* Do nothing more if multiplexer has been closed */
        if ( ! process_running ( &imux->process ) )
                return;

        /* Refill endpoints */
        if ( ( rc = usbnet_refill ( &imux->usbnet ) ) != 0 ) {
                /* Wait for next poll */
                return;
        }

        /* Perform pending action, if any */
        if ( imux->action ) {
                if ( ( rc = imux->action ( imux ) ) != 0 )
                        imux_close ( imux, rc );
                imux->action = NULL;
        }
}

/** Multiplexer process descriptor */
static struct process_descriptor imux_process_desc =
        PROC_DESC ( struct imux, process, imux_step );

/**
 * Probe device
 *
 * @v func              USB function
 * @v config            Configuration descriptor
 * @ret rc              Return status code
 */
static int imux_probe ( struct usb_function *func,
                        struct usb_configuration_descriptor *config ) {
        struct usb_device *usb = func->usb;
        struct imux *imux;
        int rc;

        /* Allocate and initialise structure */
        imux = zalloc ( sizeof ( *imux ) );
        if ( ! imux ) {
                rc = -ENOMEM;
                goto err_alloc;
        }
        ref_init ( &imux->refcnt, NULL );
        imux->usb = usb;
        imux->bus = usb->port->hub->bus;
        usbnet_init ( &imux->usbnet, func, NULL, &imux_in_operations,
                      &imux_out_operations );
        usb_refill_init ( &imux->usbnet.in, 0, IMUX_IN_MTU, IMUX_IN_MAX_FILL );
        process_init ( &imux->process, &imux_process_desc, &imux->refcnt );
        imux->action = imux_tx_version;
        imux->port = IMUX_PORT_LOCAL;
        intf_init ( &imux->tcp, &imux_tcp_desc, &imux->refcnt );
        imux->rc = -EINPROGRESS_PAIRING;

        /* Describe USB network device */
        if ( ( rc = usbnet_describe ( &imux->usbnet, config ) ) != 0 ) {
                DBGC ( imux, "IMUX %p could not describe: %s\n",
                       imux, strerror ( rc ) );
                goto err_describe;
        }

        /* Open USB network device */
        if ( ( rc = usbnet_open ( &imux->usbnet ) ) != 0 ) {
                DBGC ( imux, "IMUX %p could not open: %s\n",
                       imux, strerror ( rc ) );
                goto err_open;
        }

        /* Start polling process */
        process_add ( &imux->process );

        /* Add to list of multiplexers */
        list_add ( &imux->list, &imuxes );

        usb_func_set_drvdata ( func, imux );
        return 0;

        list_del ( &imux->list );
        imux_shutdown ( imux );
 err_open:
 err_describe:
        ref_put ( &imux->refcnt );
 err_alloc:
        return rc;
}

/**
 * Remove device
 *
 * @v func              USB function
 */
static void imux_remove ( struct usb_function *func ) {
        struct imux *imux = usb_func_get_drvdata ( func );

        list_del ( &imux->list );
        imux_shutdown ( imux );
        ref_put ( &imux->refcnt );
}

/** USB multiplexer device IDs */
static struct usb_device_id imux_ids[] = {
        {
                .name = "imux",
                .vendor = 0x05ac,
                .product = USB_ANY_ID,
        },
};

/** USB multiplexer driver */
struct usb_driver imux_driver __usb_driver = {
        .ids = imux_ids,
        .id_count = ( sizeof ( imux_ids ) / sizeof ( imux_ids[0] ) ),
        .class = USB_CLASS_ID ( 0xff, 0xfe, 0x02 ),
        .score = USB_SCORE_NORMAL,
        .probe = imux_probe,
        .remove = imux_remove,
};

/******************************************************************************
 *
 * iPhone pairing client
 *
 ******************************************************************************
 */

/** Common prefix for all pairing messages */
static const char ipair_prefix[] =
        "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n"
        "<!DOCTYPE plist PUBLIC \"-//Apple//DTD PLIST 1.0//EN\" "
        "\"http://www.apple.com/DTDs/PropertyList-1.0.dtd\">\n"
        "<plist version=\"1.0\">\n"
        "<dict>\n"
        "<key>Label</key>\n"
        "<string>iPXE</string>\n"
        "<key>Request</key>\n";

/** Common suffix for all pairing messages */
static const char ipair_suffix[] =
        "</dict>\n"
        "</plist>\n";

/** Arbitrary system BUID used for pairing */
static const char ipair_system_buid[] = "E4DB92D2-248A-469A-AC34-92045D07E695";

/** Arbitrary host ID used for pairing */
static const char ipair_host_id[] = "93CEBC27-8457-4804-9108-F42549DF6143";

static int ipair_tx_pubkey ( struct ipair *ipair );
static int ipair_rx_pubkey ( struct ipair *ipair, char *msg );
static int ipair_tx_pair ( struct ipair *ipair );
static int ipair_rx_pair ( struct ipair *ipair, char *msg );
static int ipair_tx_session ( struct ipair *ipair );
static int ipair_rx_session ( struct ipair *ipair, char *msg );

/**
 * Free pairing client
 *
 * @v refcnt            Reference counter
 */
static void ipair_free ( struct refcnt *refcnt ) {
        struct ipair *ipair = container_of ( refcnt, struct ipair, refcnt );

        icert_free ( &ipair->icert );
        free ( ipair );
}

/**
 * Shut down pairing client
 *
 * @v ipair             Pairing client
 * @v rc                Reason for close
 */
static void ipair_close ( struct ipair *ipair, int rc ) {

        /* Shut down interfaces */
        intf_shutdown ( &ipair->xfer, rc );

        /* Stop timer */
        stop_timer ( &ipair->timer );
}

/**
 * Transmit XML message
 *
 * @v ipair             Pairing client
 * @v fmt               Format string
 * @v ...               Arguments
 * @ret rc              Return status code
 */
static int __attribute__ (( format ( printf, 2, 3 ) ))
ipair_tx ( struct ipair *ipair, const char *fmt, ... ) {
        struct io_buffer *iobuf;
        struct ipair_header *hdr;
        va_list args;
        size_t len;
        char *msg;
        int rc;

        /* Calculate length of formatted string */
        va_start ( args, fmt );
        len = ( vsnprintf ( NULL, 0, fmt, args ) + 1 /* NUL */ );
        va_end ( args );

        /* Allocate I/O buffer */
        iobuf = xfer_alloc_iob ( &ipair->xfer, ( sizeof ( *hdr ) + len ) );
        if ( ! iobuf )
                return -ENOMEM;
        hdr = iob_put ( iobuf, sizeof ( *hdr ) );

        /* Construct XML message */
        memset ( hdr, 0, sizeof ( *hdr ) );
        hdr->len = htonl ( len );
        msg = iob_put ( iobuf, len );
        va_start ( args, fmt );
        vsnprintf ( msg, len, fmt, args );
        va_end ( args );
        DBGC2 ( ipair, "IPAIR %p transmitting:\n%s\n", ipair, msg );

        /* Transmit message */
        if ( ( rc = xfer_deliver_iob ( &ipair->xfer,
                                       iob_disown ( iobuf ) ) ) != 0 )
                return rc;

        return 0;
}

/**
 * Receive XML message payload
 *
 * @v ipair             Pairing client
 * @v msg               Message payload
 * @v len               Length of message
 * @ret rc              Return status code
 */
static int ipair_rx ( struct ipair *ipair, char *msg, size_t len ) {
        int ( * rx ) ( struct ipair *ipair, char *msg );
        int rc;

        /* Ignore empty messages */
        if ( ! len )
                return 0;

        /* Sanity check */
        if ( ( msg[ len - 1 ] != '\0' ) && ( msg[ len - 1 ] != '\n' ) ) {
                DBGC ( ipair, "IPAIR %p malformed XML:\n", ipair );
                DBGC_HDA ( ipair, 0, msg, len );
                return -EPROTO;
        }

        /* Add NUL terminator (potentially overwriting final newline) */
        msg[ len - 1 ] = '\0';
        DBGC2 ( ipair, "IPAIR %p received:\n%s\n\n", ipair, msg );

        /* Handle according to current state */
        rx = ipair->rx;
        if ( ! rx ) {
                DBGC ( ipair, "IPAIR %p unexpected XML:\n%s\n", ipair, msg );
                return -EPROTO;
        }
        ipair->rx = NULL;
        if ( ( rc = rx ( ipair, msg ) ) != 0 )
                return rc;

        return 0;
}

/**
 * Locate XML tag
 *
 * @v ipair             Pairing client
 * @v msg               XML message
 * @v tag               Tag name
 * @ret start           Start of tag content
 * @ret end             End of tag content
 * @ret rc              Return status code
 */
static int ipair_tag ( struct ipair *ipair, const char *msg, const char *tag,
                       char **start, char **end ) {
        char buf[ 2 /* "</" */ + strlen ( tag ) + 1 /* ">" */ + 1 /* NUL */ ];

        /* Locate opening tag */
        sprintf ( buf, "<%s>", tag );
        *start = strstr ( msg, buf );
        if ( ! *start )
                return -ENOENT;
        *start += strlen ( buf );

        /* Locate closing tag */
        sprintf ( buf, "</%s>", tag );
        *end = strstr ( *start, buf );
        if ( ! *end ) {
                DBGC ( ipair, "IPAIR %p missing closing tag %s in:\n%s\n",
                       ipair, buf, msg );
                return -ENOENT;
        }

        return 0;
}

/**
 * Locate XML property list dictionary value
 *
 * @v ipair             Pairing client
 * @v msg               XML message
 * @v key               Key name
 * @v type              Key type
 * @ret start           Start of value content
 * @ret end             End of value content
 * @ret rc              Return status code
 */
static int ipair_key ( struct ipair *ipair, const char *msg, const char *key,
                       const char *type, char **start, char **end ) {
        int rc;

        /* Iterate over keys */
        while ( 1 ) {

                /* Locate key */
                if ( ( rc = ipair_tag ( ipair, msg, "key", start,
                                        end ) ) != 0 )
                        return rc;
                msg = *end;

                /* Check key name */
                if ( memcmp ( *start, key, ( *end - *start ) ) != 0 )
                        continue;

                /* Locate value */
                return ipair_tag ( ipair, msg, type, start, end );
        }
}

/**
 * Transmit DevicePublicKey message
 *
 * @v ipair             Pairing client
 * @ret rc              Return status code
 */
static int ipair_tx_pubkey ( struct ipair *ipair ) {
        int rc;

        /* Transmit message */
        if ( ( rc = ipair_tx ( ipair,
                               "%s"
                               "<string>GetValue</string>\n"
                               "<key>Key</key>\n"
                               "<string>DevicePublicKey</string>\n"
                               "%s",
                               ipair_prefix, ipair_suffix ) ) != 0 )
                return rc;

        return 0;
}

/**
 * Receive DevicePublicKey message
 *
 * @v ipair             Pairing client
 * @v msg               XML message
 * @ret rc              Return status code
 */
static int ipair_rx_pubkey ( struct ipair *ipair, char *msg ) {
        struct asn1_cursor *key;
        char *data;
        char *end;
        char *decoded;
        size_t max_len;
        int len;
        int next;
        int rc;

        /* Locate "Value" value */
        if ( ( rc = ipair_key ( ipair, msg, "Value", "data", &data,
                                &end ) ) != 0 ) {
                DBGC ( ipair, "IPAIR %p unexpected public key message:\n%s\n",
                       ipair, msg );
                goto err_tag;
        }
        *end = '\0';

        /* Decode outer layer of Base64 */
        max_len = base64_decoded_max_len ( data );
        decoded = malloc ( max_len );
        if ( ! decoded ) {
                rc = -ENOMEM;
                goto err_alloc;
        }
        len = base64_decode ( data, decoded, max_len );
        if ( len < 0 ) {
                rc = len;
                DBGC ( ipair, "IPAIR %p invalid outer public key:\n%s\n",
                       ipair, data );
                goto err_decode;
        }

        /* Decode inner layer of Base64 */
        next = pem_asn1 ( decoded, len, 0, &key );
        if ( next < 0 ) {
                rc = next;
                DBGC ( ipair, "IPAIR %p invalid inner public key:\n%s\n",
                       ipair, decoded );
                goto err_asn1;
        }
        DBGC ( ipair, "IPAIR %p received public key\n", ipair );
        DBGC2_HDA ( ipair, 0, key->data, key->len );

        /* Construct certificates */
        if ( ( rc = icert_certs ( &ipair->icert, key ) ) != 0 )
                goto err_certs;

        /* Send session request or pair request as applicable */
        if ( ipair->flags & IPAIR_REQUEST ) {
                ipair->tx = ipair_tx_pair;
                ipair->rx = ipair_rx_pair;
        } else {
                ipair->tx = ipair_tx_session;
                ipair->rx = ipair_rx_session;
        }
        start_timer_nodelay ( &ipair->timer );

        /* Free key */
        free ( key );

        /* Free intermediate Base64 */
        free ( decoded );

        return 0;

 err_certs:
        free ( key );
 err_asn1:
 err_decode:
        free ( decoded );
 err_alloc:
 err_tag:
        return rc;
}

/**
 * Transmit Pair message
 *
 * @v ipair             Pairing client
 * @ret rc              Return status code
 */
static int ipair_tx_pair ( struct ipair *ipair ) {
        char *root;
        char *host;
        char *device;
        int rc;

        /* Construct doubly encoded certificates */
        if ( ( rc = icert_encode ( &ipair->icert, ipair->icert.root,
                                   &root ) ) != 0 )
                goto err_root;
        if ( ( rc = icert_encode ( &ipair->icert, ipair->icert.host,
                                   &host ) ) != 0 )
                goto err_host;
        if ( ( rc = icert_encode ( &ipair->icert, ipair->icert.device,
                                   &device ) ) != 0 )
                goto err_device;

        /* Transmit message */
        if ( ( rc = ipair_tx ( ipair,
                               "%s"
                               "<string>Pair</string>\n"
                               "<key>PairRecord</key>\n"
                               "<dict>\n"
                               "<key>RootCertificate</key>\n"
                               "<data>%s</data>\n"
                               "<key>HostCertificate</key>\n"
                               "<data>%s</data>\n"
                               "<key>DeviceCertificate</key>\n"
                               "<data>%s</data>\n"
                               "<key>SystemBUID</key>\n"
                               "<string>%s</string>\n"
                               "<key>HostID</key>\n"
                               "<string>%s</string>\n"
                               "</dict>\n"
                               "<key>ProtocolVersion</key>\n"
                               "<string>2</string>\n"
                               "<key>PairingOptions</key>\n"
                               "<dict>\n"
                               "<key>ExtendedPairingErrors</key>\n"
                               "<true/>\n"
                               "</dict>\n"
                               "%s",
                               ipair_prefix, root, host, device,
                               ipair_system_buid, ipair_host_id,
                               ipair_suffix
                               ) ) != 0 )
                goto err_tx;

 err_tx:
        free ( device );
 err_device:
        free ( host );
 err_host:
        free ( root );
 err_root:
        return rc;
}

/**
 * Receive Pair message error
 *
 * @v ipair             Pairing client
 * @v error             Pairing error
 * @ret rc              Return status code
 */
static int ipair_rx_pair_error ( struct ipair *ipair, char *error ) {

        /* Check for actual errors */
        if ( strcmp ( error, "PairingDialogResponsePending" ) != 0 ) {
                DBGC ( ipair, "IPAIR %p pairing error \"%s\"\n", ipair, error );
                return -EPERM;
        }

        /* Retransmit pairing request */
        ipair->tx = ipair_tx_pair;
        ipair->rx = ipair_rx_pair;
        start_timer_fixed ( &ipair->timer, IPAIR_RETRY_DELAY );

        DBGC ( ipair, "IPAIR %p waiting for pairing dialog\n", ipair );
        return 0;
}

/**
 * Receive Pair message
 *
 * @v ipair             Pairing client
 * @v msg               XML message
 * @ret rc              Return status code
 */
static int ipair_rx_pair ( struct ipair *ipair, char *msg ) {
        char *error;
        char *escrow;
        char *end;
        int rc;

        /* Check for pairing errors */
        if ( ( rc = ipair_key ( ipair, msg, "Error", "string", &error,
                                &end ) ) == 0 ) {
                *end = '\0';
                return ipair_rx_pair_error ( ipair, error );
        }

        /* Get EscrowBag */
        if ( ( rc = ipair_key ( ipair, msg, "EscrowBag", "data", &escrow,
                                &end ) ) != 0 ) {
                DBGC ( ipair, "IPAIR %p unexpected pairing response:\n%s\n",
                       ipair, msg );
                return rc;
        }
        DBGC ( ipair, "IPAIR %p pairing successful\n", ipair );

        /* Send session request */
        ipair->tx = ipair_tx_session;
        ipair->rx = ipair_rx_session;
        start_timer_nodelay ( &ipair->timer );

        return 0;
}

/**
 * Transmit StartSession message
 *
 * @v ipair             Pairing client
 * @ret rc              Return status code
 */
static int ipair_tx_session ( struct ipair *ipair ) {
        int rc;

        /* Transmit message */
        if ( ( rc = ipair_tx ( ipair,
                               "%s"
                               "<string>StartSession</string>\n"
                               "<key>SystemBUID</key>\n"
                               "<string>%s</string>\n"
                               "<key>HostID</key>\n"
                               "<string>%s</string>\n"
                               "%s",
                               ipair_prefix, ipair_system_buid,
                               ipair_host_id, ipair_suffix
                               ) ) != 0 )
                return rc;

        return 0;
}

/**
 * Receive StartSession message error
 *
 * @v ipair             Pairing client
 * @v error             Pairing error
 * @ret rc              Return status code
 */
static int ipair_rx_session_error ( struct ipair *ipair, char *error ) {

        /* Check for actual errors */
        if ( strcmp ( error, "InvalidHostID" ) != 0 ) {
                DBGC ( ipair, "IPAIR %p session error \"%s\"\n", ipair, error );
                return -EPERM;
        }

        /* Transmit pairing request */
        ipair->tx = ipair_tx_pair;
        ipair->rx = ipair_rx_pair;
        start_timer_nodelay ( &ipair->timer );

        DBGC ( ipair, "IPAIR %p unknown host: requesting pairing\n", ipair );
        return 0;
}

/**
 * Receive StartSession message
 *
 * @v ipair             Pairing client
 * @v msg               XML message
 * @ret rc              Return status code
 */
static int ipair_rx_session ( struct ipair *ipair, char *msg ) {
        char *error;
        char *session;
        char *end;
        int rc;

        /* Check for session errors */
        if ( ( rc = ipair_key ( ipair, msg, "Error", "string", &error,
                                &end ) ) == 0 ) {
                *end = '\0';
                return ipair_rx_session_error ( ipair, error );
        }

        /* Check for session ID */
        if ( ( rc = ipair_key ( ipair, msg, "SessionID", "string", &session,
                                &end ) ) != 0 ) {
                DBGC ( ipair, "IPAIR %p unexpected session response:\n%s\n",
                       ipair, msg );
                return rc;
        }
        *end = '\0';
        DBGC ( ipair, "IPAIR %p starting session \"%s\"\n", ipair, session );

        /* Start TLS */
        if ( ( rc = add_tls ( &ipair->xfer, "iPhone", &icert_root,
                              ipair->icert.key ) ) != 0 ) {
                DBGC ( ipair, "IPAIR %p could not start TLS: %s\n",
                       ipair, strerror ( rc ) );
                return rc;
        }

        /* Record that TLS has been started */
        ipair->flags |= IPAIR_TLS;

        return 0;
}

/**
 * Handle window change notification
 *
 * @v ipair             Pairing client
 */
static void ipair_window_changed ( struct ipair *ipair ) {

        /* Report pairing as complete once TLS session has been established */
        if ( ( ipair->flags & IPAIR_TLS ) && xfer_window ( &ipair->xfer ) ) {

                /* Sanity checks */
                assert ( x509_is_valid ( ipair->icert.root, &icert_root ) );
                assert ( x509_is_valid ( ipair->icert.device, &icert_root ) );
                assert ( ! x509_is_valid ( ipair->icert.root, NULL ) );
                assert ( ! x509_is_valid ( ipair->icert.host, NULL ) );
                assert ( ! x509_is_valid ( ipair->icert.device, NULL ) );

                /* Report pairing as complete */
                DBGC ( ipair, "IPAIR %p established TLS session\n", ipair );
                ipair_close ( ipair, 0 );
                return;
        }
}

/**
 * Handle received data
 *
 * @v ipair             Pairing client
 * @v iobuf             I/O buffer
 * @v meta              Data transfer metadata
 * @ret rc              Return status code
 */
static int ipair_deliver ( struct ipair *ipair, struct io_buffer *iobuf,
                           struct xfer_metadata *meta __unused ) {
        struct ipair_header *hdr;
        int rc;

        /* Strip header (which may appear in a separate packet) */
        if ( ( ! ( ipair->flags & IPAIR_RX_LEN ) ) &&
             ( iob_len ( iobuf ) >= sizeof ( *hdr ) ) ) {
                iob_pull ( iobuf, sizeof ( *hdr ) );
                ipair->flags |= IPAIR_RX_LEN;
        }

        /* Clear received header flag if we have a message */
        if ( iob_len ( iobuf ) )
                ipair->flags &= ~IPAIR_RX_LEN;

        /* Receive message */
        if ( ( rc = ipair_rx ( ipair, iobuf->data, iob_len ( iobuf ) ) ) != 0 )
                goto error;

        /* Free I/O buffer */
        free_iob ( iobuf );

        return 0;

 error:
        ipair_close ( ipair, rc );
        free_iob ( iobuf );
        return rc;
}

/**
 * Pairing transmission timer
 *
 * @v timer             Retransmission timer
 * @v over              Failure indicator
 */
static void ipair_expired ( struct retry_timer *timer, int over __unused ) {
        struct ipair *ipair = container_of ( timer, struct ipair, timer );
        int ( * tx ) ( struct ipair *ipair );
        int rc;

        /* Sanity check */
        tx = ipair->tx;
        assert ( tx != NULL );

        /* Clear pending transmission */
        ipair->tx = NULL;

        /* Transmit data, if applicable */
        if ( ( rc = tx ( ipair ) ) != 0 )
                ipair_close ( ipair, rc );
}

/** Pairing client interface operations */
static struct interface_operation ipair_xfer_operations[] = {
        INTF_OP ( xfer_deliver, struct ipair *, ipair_deliver ),
        INTF_OP ( xfer_window_changed, struct ipair *, ipair_window_changed ),
        INTF_OP ( intf_close, struct ipair *, ipair_close ),
};

/** Pairing client interface descriptor */
static struct interface_descriptor ipair_xfer_desc =
        INTF_DESC ( struct ipair, xfer, ipair_xfer_operations );

/**
 * Create a pairing client
 *
 * @v xfer              Data transfer interface
 * @v flags             Initial state flags
 * @ret rc              Return status code
 */
static int ipair_create ( struct interface *xfer, unsigned int flags ) {
        struct ipair *ipair;
        int rc;

        /* Allocate and initialise structure */
        ipair = zalloc ( sizeof ( *ipair ) );
        if ( ! ipair ) {
                rc = -ENOMEM;
                goto err_alloc;
        }
        ref_init ( &ipair->refcnt, ipair_free );
        intf_init ( &ipair->xfer, &ipair_xfer_desc, &ipair->refcnt );
        timer_init ( &ipair->timer, ipair_expired, &ipair->refcnt );
        ipair->tx = ipair_tx_pubkey;
        ipair->rx = ipair_rx_pubkey;
        ipair->flags = flags;

        /* Schedule initial transmission */
        start_timer_nodelay ( &ipair->timer );

        /* Attach to parent interface, mortalise self, and return */
        intf_plug_plug ( &ipair->xfer, xfer );
        ref_put ( &ipair->refcnt );
        return 0;

        ref_put ( &ipair->refcnt );
 err_alloc:
        return rc;
}

/******************************************************************************
 *
 * iPhone USB networking
 *
 ******************************************************************************
 */

/**
 * Complete bulk IN transfer
 *
 * @v ep                USB endpoint
 * @v iobuf             I/O buffer
 * @v rc                Completion status code
 */
static void iphone_in_complete ( struct usb_endpoint *ep,
                                 struct io_buffer *iobuf, int rc ) {
        struct iphone *iphone = container_of ( ep, struct iphone, usbnet.in );
        struct net_device *netdev = iphone->netdev;

        /* Profile receive completions */
        profile_start ( &iphone_in_profiler );

        /* Ignore packets cancelled when the endpoint closes */
        if ( ! ep->open )
                goto ignore;

        /* Record USB errors against the network device */
        if ( rc != 0 ) {
                DBGC ( iphone, "IPHONE %p bulk IN failed: %s\n",
                       iphone, strerror ( rc ) );
                goto error;
        }

        /* Strip padding */
        if ( iob_len ( iobuf ) < IPHONE_IN_PAD ) {
                DBGC ( iphone, "IPHONE %p malformed bulk IN:\n", iphone );
                DBGC_HDA ( iphone, 0, iobuf->data, iob_len ( iobuf ) );
                rc = -EINVAL;
                goto error;
        }
        iob_pull ( iobuf, IPHONE_IN_PAD );

        /* Hand off to network stack */
        netdev_rx ( netdev, iob_disown ( iobuf ) );

        profile_stop ( &iphone_in_profiler );
        return;

 error:
        netdev_rx_err ( netdev, iob_disown ( iobuf ), rc );
 ignore:
        free_iob ( iobuf );
}

/** Bulk IN endpoint operations */
static struct usb_endpoint_driver_operations iphone_in_operations = {
        .complete = iphone_in_complete,
};

/**
 * Transmit packet
 *
 * @v iphone            iPhone device
 * @v iobuf             I/O buffer
 * @ret rc              Return status code
 */
static int iphone_out_transmit ( struct iphone *iphone,
                                 struct io_buffer *iobuf ) {
        int rc;

        /* Profile transmissions */
        profile_start ( &iphone_out_profiler );

        /* Enqueue I/O buffer */
        if ( ( rc = usb_stream ( &iphone->usbnet.out, iobuf, 1 ) ) != 0 )
                return rc;

        profile_stop ( &iphone_out_profiler );
        return 0;
}

/**
 * Complete bulk OUT transfer
 *
 * @v ep                USB endpoint
 * @v iobuf             I/O buffer
 * @v rc                Completion status code
 */
static void iphone_out_complete ( struct usb_endpoint *ep,
                                  struct io_buffer *iobuf, int rc ) {
        struct iphone *iphone = container_of ( ep, struct iphone, usbnet.out );
        struct net_device *netdev = iphone->netdev;

        /* Report TX completion */
        netdev_tx_complete_err ( netdev, iobuf, rc );
}

/** Bulk OUT endpoint operations */
static struct usb_endpoint_driver_operations iphone_out_operations = {
        .complete = iphone_out_complete,
};

/**
 * Check pairing status
 *
 * @v iphone            iPhone device
 * @ret rc              Return status code
 */
static int iphone_check_pair ( struct iphone *iphone ) {
        struct imux *imux;

        /* Find corresponding USB multiplexer */
        list_for_each_entry ( imux, &imuxes, list ) {
                if ( imux->usb == iphone->usb )
                        return imux->rc;
        }

        return -EPIPE_NO_MUX;
}

/**
 * Check link status
 *
 * @v netdev            Network device
 */
static void iphone_check_link ( struct net_device *netdev ) {
        struct iphone *iphone = netdev->priv;
        struct usb_device *usb = iphone->usb;
        uint8_t status;
        int rc;

        /* Check pairing status */
        if ( ( rc = iphone_check_pair ( iphone ) ) != 0 )
                goto err_pair;

        /* Get link status */
        if ( ( rc = usb_control ( usb, IPHONE_GET_LINK, 0, 0, &status,
                                  sizeof ( status ) ) ) != 0 ) {
                DBGC ( iphone, "IPHONE %p could not get link status: %s\n",
                       iphone, strerror ( rc ) );
                goto err_control;
        }

        /* Check link status */
        if ( status != IPHONE_LINK_UP ) {
                rc = -ENOTCONN_STATUS ( status );
                goto err_status;
        }

        /* Success */
        rc = 0;

 err_status:
 err_control:
 err_pair:
        /* Report link status.  Since we have to check the link
         * periodically (due to an absence of an interrupt endpoint),
         * do this only if the link status has actually changed.
         */
        if ( rc != netdev->link_rc ) {
                if ( rc == 0 ) {
                        DBGC ( iphone, "IPHONE %p link up\n", iphone );
                } else {
                        DBGC ( iphone, "IPHONE %p link down: %s\n",
                               iphone, strerror ( rc ) );
                }
                netdev_link_err ( netdev, rc );
        }
}

/**
 * Periodically update link status
 *
 * @v timer             Link status timer
 * @v over              Failure indicator
 */
static void iphone_expired ( struct retry_timer *timer, int over __unused ) {
        struct iphone *iphone = container_of ( timer, struct iphone, timer );
        struct net_device *netdev = iphone->netdev;

        /* Check link status */
        iphone_check_link ( netdev );

        /* Restart timer, if device is open */
        if ( netdev_is_open ( netdev ) )
                start_timer_fixed ( timer, IPHONE_LINK_CHECK_INTERVAL );
}

/**
 * Open network device
 *
 * @v netdev            Network device
 * @ret rc              Return status code
 */
static int iphone_open ( struct net_device *netdev ) {
        struct iphone *iphone = netdev->priv;
        int rc;

        /* Open USB network device */
        if ( ( rc = usbnet_open ( &iphone->usbnet ) ) != 0 ) {
                DBGC ( iphone, "IPHONE %p could not open: %s\n",
                       iphone, strerror ( rc ) );
                goto err_open;
        }

        /* Start the link status check timer */
        start_timer_nodelay ( &iphone->timer );

        return 0;

        usbnet_close ( &iphone->usbnet );
 err_open:
        return rc;
}

/**
 * Close network device
 *
 * @v netdev            Network device
 */
static void iphone_close ( struct net_device *netdev ) {
        struct iphone *iphone = netdev->priv;

        /* Stop the link status check timer */
        stop_timer ( &iphone->timer );

        /* Close USB network device */
        usbnet_close ( &iphone->usbnet );
}

/**
 * Transmit packet
 *
 * @v netdev            Network device
 * @v iobuf             I/O buffer
 * @ret rc              Return status code
 */
static int iphone_transmit ( struct net_device *netdev,
                             struct io_buffer *iobuf ) {
        struct iphone *iphone = netdev->priv;
        int rc;

        /* Transmit packet */
        if ( ( rc = iphone_out_transmit ( iphone, iobuf ) ) != 0 )
                return rc;

        return 0;
}

/**
 * Poll for completed and received packets
 *
 * @v netdev            Network device
 */
static void iphone_poll ( struct net_device *netdev ) {
        struct iphone *iphone = netdev->priv;
        int rc;

        /* Poll USB bus */
        usb_poll ( iphone->bus );

        /* Refill endpoints */
        if ( ( rc = usbnet_refill ( &iphone->usbnet ) ) != 0 )
                netdev_rx_err ( netdev, NULL, rc );
}

/** iPhone network device operations */
static struct net_device_operations iphone_operations = {
        .open           = iphone_open,
        .close          = iphone_close,
        .transmit       = iphone_transmit,
        .poll           = iphone_poll,
};

/**
 * Probe device
 *
 * @v func              USB function
 * @v config            Configuration descriptor
 * @ret rc              Return status code
 */
static int iphone_probe ( struct usb_function *func,
                          struct usb_configuration_descriptor *config ) {
        struct usb_device *usb = func->usb;
        struct net_device *netdev;
        struct iphone *iphone;
        int rc;

        /* Allocate and initialise structure */
        netdev = alloc_etherdev ( sizeof ( *iphone ) );
        if ( ! netdev ) {
                rc = -ENOMEM;
                goto err_alloc;
        }
        netdev_init ( netdev, &iphone_operations );
        netdev->dev = &func->dev;
        iphone = netdev->priv;
        memset ( iphone, 0, sizeof ( *iphone ) );
        iphone->usb = usb;
        iphone->bus = usb->port->hub->bus;
        iphone->netdev = netdev;
        usbnet_init ( &iphone->usbnet, func, NULL, &iphone_in_operations,
                      &iphone_out_operations );
        usb_refill_init ( &iphone->usbnet.in, 0, IPHONE_IN_MTU,
                          IPHONE_IN_MAX_FILL );
        timer_init ( &iphone->timer, iphone_expired, &netdev->refcnt );
        DBGC ( iphone, "IPHONE %p on %s\n", iphone, func->name );

        /* Describe USB network device */
        if ( ( rc = usbnet_describe ( &iphone->usbnet, config ) ) != 0 ) {
                DBGC ( iphone, "IPHONE %p could not describe: %s\n",
                       iphone, strerror ( rc ) );
                goto err_describe;
        }

        /* Fetch MAC address */
        if ( ( rc = usb_control ( usb, IPHONE_GET_MAC, 0, 0, netdev->hw_addr,
                                  ETH_ALEN ) ) != 0 ) {
                DBGC ( iphone, "IPHONE %p could not fetch MAC address: %s\n",
                       iphone, strerror ( rc ) );
                goto err_fetch_mac;
        }

        /* Register network device */
        if ( ( rc = register_netdev ( netdev ) ) != 0 )
                goto err_register;

        /* Set initial link status */
        iphone_check_link ( netdev );

        /* Add to list of iPhone network devices */
        list_add ( &iphone->list, &iphones );

        usb_func_set_drvdata ( func, iphone );
        return 0;

        list_del ( &iphone->list );
        unregister_netdev ( netdev );
 err_register:
 err_fetch_mac:
 err_describe:
        netdev_nullify ( netdev );
        netdev_put ( netdev );
 err_alloc:
        return rc;
}

/**
 * Remove device
 *
 * @v func              USB function
 */
static void iphone_remove ( struct usb_function *func ) {
        struct iphone *iphone = usb_func_get_drvdata ( func );
        struct net_device *netdev = iphone->netdev;

        list_del ( &iphone->list );
        unregister_netdev ( netdev );
        netdev_nullify ( netdev );
        netdev_put ( netdev );
}

/** iPhone device IDs */
static struct usb_device_id iphone_ids[] = {
        {
                .name = "iphone",
                .vendor = 0x05ac,
                .product = USB_ANY_ID,
        },
};

/** iPhone driver */
struct usb_driver iphone_driver __usb_driver = {
        .ids = iphone_ids,
        .id_count = ( sizeof ( iphone_ids ) / sizeof ( iphone_ids[0] ) ),
        .class = USB_CLASS_ID ( 0xff, 0xfd, 0x01 ),
        .score = USB_SCORE_NORMAL,
        .probe = iphone_probe,
        .remove = iphone_remove,
};

/* Drag in objects via iphone_driver */
REQUIRING_SYMBOL ( iphone_driver );

/* Drag in RSA-with-SHA256 OID prefixes */
REQUIRE_OBJECT ( rsa_sha256 );