httpdigest.c

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/*
 * Copyright (C) 2015 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 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 );

/**
 * @file
 *
 * Hyper Text Transfer Protocol (HTTP) Digest authentication
 *
 */

#include <stdio.h>
#include <errno.h>
#include <strings.h>
#include <ipxe/uri.h>
#include <ipxe/md5.h>
#include <ipxe/base16.h>
#include <ipxe/vsprintf.h>
#include <ipxe/http.h>

/* Disambiguate the various error causes */
#define EACCES_USERNAME __einfo_error ( EINFO_EACCES_USERNAME )
#define EINFO_EACCES_USERNAME                                           \
        __einfo_uniqify ( EINFO_EACCES, 0x01,                           \
                          "No username available for Digest authentication" )

/** An HTTP Digest "WWW-Authenticate" response field */
struct http_digest_field {
        /** Name */
        const char *name;
        /** Offset */
        size_t offset;
};

/** Define an HTTP Digest "WWW-Authenticate" response field */
#define HTTP_DIGEST_FIELD( _name ) {                                    \
                .name = #_name,                                         \
                .offset = offsetof ( struct http_transaction,           \
                                     response.auth.digest._name ),      \
        }

/**
 * Set HTTP Digest "WWW-Authenticate" response field value
 *
 * @v http              HTTP transaction
 * @v field             Response field
 * @v value             Field value
 */
static inline void
http_digest_field ( struct http_transaction *http,
                    struct http_digest_field *field, char *value ) {
        char **ptr;

        ptr = ( ( ( void * ) http ) + field->offset );
        *ptr = value;
}

/** HTTP Digest "WWW-Authenticate" fields */
static struct http_digest_field http_digest_fields[] = {
        HTTP_DIGEST_FIELD ( realm ),
        HTTP_DIGEST_FIELD ( qop ),
        HTTP_DIGEST_FIELD ( algorithm ),
        HTTP_DIGEST_FIELD ( nonce ),
        HTTP_DIGEST_FIELD ( opaque ),
};

/**
 * Parse HTTP "WWW-Authenticate" header for Digest authentication
 *
 * @v http              HTTP transaction
 * @v line              Remaining header line
 * @ret rc              Return status code
 */
static int http_parse_digest_auth ( struct http_transaction *http,
                                    char *line ) {
        struct http_digest_field *field;
        char *key;
        char *value;
        unsigned int i;

        /* Process fields */
        while ( ( key = http_token ( &line, &value ) ) ) {
                for ( i = 0 ; i < ( sizeof ( http_digest_fields ) /
                                    sizeof ( http_digest_fields[0] ) ) ; i++){
                        field = &http_digest_fields[i];
                        if ( strcasecmp ( key, field->name ) == 0 )
                                http_digest_field ( http, field, value );
                }
        }

        /* Allow HTTP request to be retried if the request had not
         * already tried authentication.
         */
        if ( ! http->request.auth.auth )
                http->response.flags |= HTTP_RESPONSE_RETRY;

        return 0;
}

/**
 * Initialise HTTP Digest
 *
 * @v ctx               Digest context
 * @v string            Initial string
 */
static void http_digest_init ( struct md5_context *ctx ) {

        /* Initialise MD5 digest */
        digest_init ( &md5_algorithm, ctx );
}

/**
 * Update HTTP Digest with new data
 *
 * @v ctx               Digest context
 * @v string            String to append
 */
static void http_digest_update ( struct md5_context *ctx, const char *string ) {
        static const char colon = ':';

        /* Add (possibly colon-separated) field to MD5 digest */
        if ( ctx->len )
                digest_update ( &md5_algorithm, ctx, &colon, sizeof ( colon ) );
        digest_update ( &md5_algorithm, ctx, string, strlen ( string ) );
}

/**
 * Finalise HTTP Digest
 *
 * @v ctx               Digest context
 * @v out               Buffer for digest output
 * @v len               Buffer length
 */
static void http_digest_final ( struct md5_context *ctx, char *out,
                                size_t len ) {
        uint8_t digest[MD5_DIGEST_SIZE];

        /* Finalise and base16-encode MD5 digest */
        digest_final ( &md5_algorithm, ctx, digest );
        base16_encode ( digest, sizeof ( digest ), out, len );
}

/**
 * Perform HTTP Digest authentication
 *
 * @v http              HTTP transaction
 * @ret rc              Return status code
 */
static int http_digest_authenticate ( struct http_transaction *http ) {
        struct http_request_auth_digest *req = &http->request.auth.digest;
        struct http_response_auth_digest *rsp = &http->response.auth.digest;
        char ha1[ base16_encoded_len ( MD5_DIGEST_SIZE ) + 1 /* NUL */ ];
        char ha2[ base16_encoded_len ( MD5_DIGEST_SIZE ) + 1 /* NUL */ ];
        static const char md5sess[] = "MD5-sess";
        static const char md5[] = "MD5";
        struct md5_context ctx;
        const char *password;

        /* Check for required response parameters */
        if ( ! rsp->realm ) {
                DBGC ( http, "HTTP %p has no realm for Digest authentication\n",
                       http );
                return -EINVAL;
        }
        if ( ! rsp->nonce ) {
                DBGC ( http, "HTTP %p has no nonce for Digest authentication\n",
                       http );
                return -EINVAL;
        }

        /* Record username and password */
        if ( ! http->uri->user ) {
                DBGC ( http, "HTTP %p has no username for Digest "
                       "authentication\n", http );
                return -EACCES_USERNAME;
        }
        req->username = http->uri->user;
        password = ( http->uri->password ? http->uri->password : "" );

        /* Handle quality of protection */
        if ( rsp->qop ) {

                /* Use "auth" in subsequent request */
                req->qop = "auth";

                /* Generate a client nonce */
                snprintf ( req->cnonce, sizeof ( req->cnonce ),
                           "%08lx", random() );

                /* Determine algorithm */
                req->algorithm = md5;
                if ( rsp->algorithm &&
                     ( strcasecmp ( rsp->algorithm, md5sess ) == 0 ) ) {
                        req->algorithm = md5sess;
                }
        }

        /* Generate HA1 */
        http_digest_init ( &ctx );
        http_digest_update ( &ctx, req->username );
        http_digest_update ( &ctx, rsp->realm );
        http_digest_update ( &ctx, password );
        http_digest_final ( &ctx, ha1, sizeof ( ha1 ) );
        if ( req->algorithm == md5sess ) {
                http_digest_init ( &ctx );
                http_digest_update ( &ctx, ha1 );
                http_digest_update ( &ctx, rsp->nonce );
                http_digest_update ( &ctx, req->cnonce );
                http_digest_final ( &ctx, ha1, sizeof ( ha1 ) );
        }

        /* Generate HA2 */
        http_digest_init ( &ctx );
        http_digest_update ( &ctx, http->request.method->name );
        http_digest_update ( &ctx, http->request.uri );
        http_digest_final ( &ctx, ha2, sizeof ( ha2 ) );

        /* Generate response */
        http_digest_init ( &ctx );
        http_digest_update ( &ctx, ha1 );
        http_digest_update ( &ctx, rsp->nonce );
        if ( req->qop ) {
                http_digest_update ( &ctx, HTTP_DIGEST_NC );
                http_digest_update ( &ctx, req->cnonce );
                http_digest_update ( &ctx, req->qop );
        }
        http_digest_update ( &ctx, ha2 );
        http_digest_final ( &ctx, req->response, sizeof ( req->response ) );

        return 0;
}

/**
 * Construct HTTP "Authorization" header for Digest authentication
 *
 * @v http              HTTP transaction
 * @v buf               Buffer
 * @v len               Length of buffer
 * @ret len             Length of header value, or negative error
 */
static int http_format_digest_auth ( struct http_transaction *http,
                                     char *buf, size_t len ) {
        struct http_request_auth_digest *req = &http->request.auth.digest;
        struct http_response_auth_digest *rsp = &http->response.auth.digest;
        size_t used = 0;

        /* Sanity checks */
        assert ( rsp->realm != NULL );
        assert ( rsp->nonce != NULL );
        assert ( req->username != NULL );
        if ( req->qop ) {
                assert ( req->algorithm != NULL );
                assert ( req->cnonce[0] != '\0' );
        }
        assert ( req->response[0] != '\0' );

        /* Construct response */
        used += ssnprintf ( ( buf + used ), ( len - used ),
                            "realm=\"%s\", nonce=\"%s\", uri=\"%s\", "
                            "username=\"%s\"", rsp->realm, rsp->nonce,
                            http->request.uri, req->username );
        if ( rsp->opaque ) {
                used += ssnprintf ( ( buf + used ), ( len - used ),
                                    ", opaque=\"%s\"", rsp->opaque );
        }
        if ( req->qop ) {
                used += ssnprintf ( ( buf + used ), ( len - used ),
                                    ", qop=%s, algorithm=%s, cnonce=\"%s\", "
                                    "nc=" HTTP_DIGEST_NC, req->qop,
                                    req->algorithm, req->cnonce );
        }
        used += ssnprintf ( ( buf + used ), ( len - used ),
                            ", response=\"%s\"", req->response );

        return used;
}

/** HTTP Digest authentication scheme */
struct http_authentication http_digest_auth __http_authentication = {
        .name = "Digest",
        .parse = http_parse_digest_auth,
        .authenticate = http_digest_authenticate,
        .format = http_format_digest_auth,
};

/* Drag in HTTP authentication support */
REQUIRING_SYMBOL ( http_digest_auth );
REQUIRE_OBJECT ( httpauth );