libs/smux/ber_tlv_length.c

   1 /*-
   2  * Copyright (c) 2003, 2004 Lev Walkin <vlm@lionet.info>. All rights reserved.
   3  * Redistribution and modifications are permitted subject to BSD license.
   4  */
   5 #include <asn_internal.h>
   6 #include <ber_tlv_length.h>
   7 #include <ber_tlv_tag.h>
   8
   9 ssize_t
  10 ber_fetch_length(int _is_constructed, const void *bufptr, size_t size,
  11                 ber_tlv_len_t *len_r) {
  12         const uint8_t *buf = (const uint8_t *)bufptr;
  13         unsigned oct;
  14
  15         if(size == 0)
  16                 return 0;       /* Want more */
  17
  18         oct = *(const uint8_t *)buf;
  19         if((oct & 0x80) == 0) {
  20                 /*
  21                  * Short definite length.
  22                  */
  23                 *len_r = oct;   /* & 0x7F */
  24                 return 1;
  25         } else {
  26                 ber_tlv_len_t len;
  27                 size_t skipped;
  28
  29                 if(_is_constructed && oct == 0x80) {
  30                         *len_r = -1;    /* Indefinite length */
  31                         return 1;
  32                 }
  33
  34                 if(oct == 0xff) {
  35                         /* Reserved in standard for future use. */
  36                         return -1;
  37                 }
  38
  39                 oct &= 0x7F;    /* Leave only the 7 LS bits */
  40                 for(len = 0, buf++, skipped = 1;
  41                         oct && (++skipped <= size); buf++, oct--) {
  42
  43                         /* Verify that we won't overflow. */
  44                         if(!(len >> ((8 * sizeof(len)) - (8+1)))) {
  45                                 len = (len << 8) | *buf;
  46                         } else {
  47                                 /* Too large length value. */
  48                                 return -1;
  49                         }
  50                 }
  51
  52                 if(oct == 0) {
  53                         if(len < 0 || len > RSSIZE_MAX) {
  54                                 /* Length value out of sane range. */
  55                                 return -1;
  56                         }
  57
  58                         *len_r = len;
  59                         return skipped;
  60                 }
  61
  62                 return 0;       /* Want more */
  63         }
  64
  65 }
  66
  67 ssize_t
  68 ber_skip_length(const asn_codec_ctx_t *opt_codec_ctx,
  69                 int _is_constructed, const void *ptr, size_t size) {
  70         ber_tlv_len_t vlen;     /* Length of V in TLV */
  71         ssize_t tl;             /* Length of L in TLV */
  72         ssize_t ll;             /* Length of L in TLV */
  73         size_t skip;
  74
  75         /*
  76          * Make sure we didn't exceed the maximum stack size.
  77          */
  78         if(ASN__STACK_OVERFLOW_CHECK(opt_codec_ctx))
  79                 return -1;
  80
  81         /*
  82          * Determine the size of L in TLV.
  83          */
  84         ll = ber_fetch_length(_is_constructed, ptr, size, &vlen);
  85         if(ll <= 0) return ll;
  86
  87         /*
  88          * Definite length.
  89          */
  90         if(vlen >= 0) {
  91                 skip = ll + vlen;
  92                 if(skip > size)
  93                         return 0;       /* Want more */
  94                 return skip;
  95         }
  96
  97         /*
  98          * Indefinite length!
  99          */
 100         ASN_DEBUG("Skipping indefinite length");
 101         for(skip = ll, ptr = ((const char *)ptr) + ll, size -= ll;;) {
 102                 ber_tlv_tag_t tag;
 103
 104                 /* Fetch the tag */
 105                 tl = ber_fetch_tag(ptr, size, &tag);
 106                 if(tl <= 0) return tl;
 107
 108                 ll = ber_skip_length(opt_codec_ctx,
 109                         BER_TLV_CONSTRUCTED(ptr),
 110                         ((const char *)ptr) + tl, size - tl);
 111                 if(ll <= 0) return ll;
 112
 113                 skip += tl + ll;
 114
 115                 /*
 116                  * This may be the end of the indefinite length structure,
 117                  * two consecutive 0 octets.
 118                  * Check if it is true.
 119                  */
 120                 if(((const uint8_t *)ptr)[0] == 0
 121                 && ((const uint8_t *)ptr)[1] == 0)
 122                         return skip;
 123
 124                 ptr = ((const char *)ptr) + tl + ll;
 125                 size -= tl + ll;
 126         }
 127
 128         /* UNREACHABLE */
 129 }
 130
 131 size_t
 132 der_tlv_length_serialize(ber_tlv_len_t len, void *bufp, size_t size) {
 133         size_t required_size;   /* Size of len encoding */
 134         uint8_t *buf = (uint8_t *)bufp;
 135         uint8_t *end;
 136         int i;
 137
 138         if(len <= 127) {
 139                 /* Encoded in 1 octet */
 140                 if(size) *buf = (uint8_t)len;
 141                 return 1;
 142         }
 143
 144         /*
 145          * Compute the size of the subsequent bytes.
 146          */
 147         for(required_size = 1, i = 8; i < 8 * (int)sizeof(len); i += 8) {
 148                 if(len >> i)
 149                         required_size++;
 150                 else
 151                         break;
 152         }
 153
 154         if(size <= required_size)
 155                 return required_size + 1;
 156
 157         *buf++ = (uint8_t)(0x80 | required_size);  /* Length of the encoding */
 158
 159         /*
 160          * Produce the len encoding, space permitting.
 161          */
 162         end = buf + required_size;
 163         for(i -= 8; buf < end; i -= 8, buf++)
 164                 *buf = (uint8_t)(len >> i);
 165
 166         return required_size + 1;
 167 }
 168