der.c

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/*
 * Copyright (C) 2016 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 );

#include <stdlib.h>
#include <errno.h>
#include <assert.h>
#include <ipxe/asn1.h>
#include <ipxe/der.h>
#include <ipxe/uaccess.h>
#include <ipxe/image.h>

/** @file
 *
 * DER-encoded ASN.1 data
 *
 */

/**
 * Extract ASN.1 object from image
 *
 * @v image             DER image
 * @v offset            Offset within image
 * @v cursor            ASN.1 cursor to fill in
 * @ret next            Offset to next image, or negative error
 *
 * The caller is responsible for eventually calling free() on the
 * allocated ASN.1 cursor.
 */
static int der_asn1 ( struct image *image, size_t offset __unused,
                      struct asn1_cursor **cursor ) {
        void *data;

        /* Allocate cursor and data buffer */
        *cursor = malloc ( sizeof ( **cursor ) + image->len );
        if ( ! *cursor )
                return -ENOMEM;
        data = ( ( ( void * ) *cursor ) + sizeof ( **cursor ) );

        /* Populate cursor and data buffer */
        (*cursor)->data = data;
        (*cursor)->len = image->len;
        copy_from_user ( data, image->data, 0, image->len );

        return image->len;
}

/**
 * Probe DER image
 *
 * @v image             DER image
 * @ret rc              Return status code
 */
static int der_probe ( struct image *image ) {
        struct asn1_cursor cursor;
        uint8_t buf[8];
        size_t extra;
        int rc;

        /* Sanity check: no realistic DER image can be smaller than this */
        if ( image->len < sizeof ( buf ) )
                return -ENOEXEC;

        /* Prepare partial cursor */
        cursor.data = buf;
        cursor.len = sizeof ( buf );
        copy_from_user ( buf, image->data, 0, sizeof ( buf ) );
        extra = ( image->len - sizeof ( buf ) );

        /* Check that image begins with an ASN.1 sequence object */
        if ( ( rc = asn1_enter_partial ( &cursor, ASN1_SEQUENCE,
                                         &extra ) ) != 0 ) {
                DBGC ( image, "DER %s is not valid ASN.1: %s\n",
                       image->name, strerror ( rc ) );
                return rc;
        }

        /* Check that image comprises a single well-formed ASN.1 object */
        if ( extra != ( image->len - sizeof ( buf ) ) ) {
                DBGC ( image, "DER %s is not single ASN.1\n", image->name );
                return -ENOEXEC;
        }

        return 0;
}

/** DER image type */
struct image_type der_image_type __image_type ( PROBE_NORMAL ) = {
        .name = "DER",
        .probe = der_probe,
        .asn1 = der_asn1,
};