src/crypto/asn1.c

   1 /*
   2  * Copyright (C) 2007 Michael Brown <mbrown@fensystems.co.uk>.
   3  *
   4  * This program is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU General Public License as
   6  * published by the Free Software Foundation; either version 2 of the
   7  * License, or any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful, but
  10  * WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12  * General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, write to the Free Software
  16  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  17  */
  18
  19 #include <stdint.h>
  20 #include <stddef.h>
  21 #include <errno.h>
  22 #include <gpxe/asn1.h>
  23
  24 /** @file
  25  *
  26  * ASN.1 encoding
  27  *
  28  */
  29
  30 /**
  31  * Start parsing ASN.1 object
  32  *
  33  * @v cursor            ASN.1 object cursor
  34  * @v type              Expected type
  35  * @ret len             Length of object body, or negative error
  36  *
  37  * The object cursor will be updated to point to the start of the
  38  * object body (i.e. the first byte following the length byte(s)), and
  39  * the length of the object body (i.e. the number of bytes until the
  40  * following object tag, if any) is returned.
  41  *
  42  * If any error occurs (i.e. if the object is not of the expected
  43  * type, or if we overflow beyond the end of the ASN.1 object), then
  44  * the cursor will be invalidated and a negative value will be
  45  * returned.
  46  */
  47 static int asn1_start ( struct asn1_cursor *cursor,
  48                                unsigned int type ) {
  49         unsigned int len_len;
  50         unsigned int len;
  51         int rc;
  52
  53         /* Sanity check */
  54         if ( cursor->len < 2 /* Tag byte and first length byte */ ) {
  55                 if ( cursor->len )
  56                         DBGC ( cursor, "ASN1 %p too short\n", cursor );
  57                 rc = -EINVAL;
  58                 goto notfound;
  59         }
  60
  61         /* Check the tag byte */
  62         if ( *( ( uint8_t * ) cursor->data ) != type ) {
  63                 DBGC ( cursor, "ASN1 %p type mismatch (expected %d, got %d)\n",
  64                        cursor, type, *( ( uint8_t * ) cursor->data ) );
  65                 rc = -ENXIO;
  66                 goto notfound;
  67         }
  68         cursor->data++;
  69         cursor->len--;
  70
  71         /* Extract length of the length field and sanity check */
  72         len_len = *( ( uint8_t * ) cursor->data );
  73         if ( len_len & 0x80 ) {
  74                 len_len = ( len_len & 0x7f );
  75                 cursor->data++;
  76                 cursor->len--;
  77         } else {
  78                 len_len = 1;
  79         }
  80         if ( cursor->len < len_len ) {
  81                 DBGC ( cursor, "ASN1 %p bad length field length %d (max "
  82                        "%zd)\n", cursor, len_len, cursor->len );
  83                 rc = -EINVAL;
  84                 goto notfound;
  85         }
  86
  87         /* Extract the length and sanity check */
  88         for ( len = 0 ; len_len ; len_len-- ) {
  89                 len <<= 8;
  90                 len |= *( ( uint8_t * ) cursor->data );
  91                 cursor->data++;
  92                 cursor->len--;
  93         }
  94         if ( cursor->len < len ) {
  95                 DBGC ( cursor, "ASN1 %p bad length %d (max %zd)\n",
  96                        cursor, len, cursor->len );
  97                 rc = -EINVAL;
  98                 goto notfound;
  99         }
 100
 101         return len;
 102
 103  notfound:
 104         cursor->data = NULL;
 105         cursor->len = 0;
 106         return rc;
 107 }
 108
 109 /**
 110  * Enter ASN.1 object
 111  *
 112  * @v cursor            ASN.1 object cursor
 113  * @v type              Expected type
 114  * @ret rc              Return status code
 115  *
 116  * The object cursor will be updated to point to the body of the
 117  * current ASN.1 object.  If any error occurs, the object cursor will
 118  * be invalidated.
 119  */
 120 int asn1_enter ( struct asn1_cursor *cursor, unsigned int type ) {
 121         int len;
 122
 123         len = asn1_start ( cursor, type );
 124         if ( len < 0 )
 125                 return len;
 126
 127         cursor->len = len;
 128         DBGC ( cursor, "ASN1 %p entered object type %02x (len %x)\n",
 129                cursor, type, len );
 130
 131         return 0;
 132 }
 133
 134 /**
 135  * Skip ASN.1 object
 136  *
 137  * @v cursor            ASN.1 object cursor
 138  * @v type              Expected type
 139  * @ret rc              Return status code
 140  *
 141  * The object cursor will be updated to point to the next ASN.1
 142  * object.  If any error occurs, the object cursor will be
 143  * invalidated.
 144  */
 145 int asn1_skip ( struct asn1_cursor *cursor, unsigned int type ) {
 146         int len;
 147
 148         len = asn1_start ( cursor, type );
 149         if ( len < 0 )
 150                 return len;
 151
 152         cursor->data += len;
 153         cursor->len -= len;
 154         DBGC ( cursor, "ASN1 %p skipped object type %02x (len %x)\n",
 155                cursor, type, len );
 156
 157         if ( ! cursor->len ) {
 158                 DBGC ( cursor, "ASN1 %p reached end of object\n", cursor );
 159                 cursor->data = NULL;
 160                 return -ENOENT;
 161         }
 162
 163         return 0;
 164 }