inet/inet6_option.c

   1 /* Copyright (C) 2003-2024 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <https://www.gnu.org/licenses/>.  */
  17
  18 #include <assert.h>
  19 #include <string.h>
  20 #include <netinet/in.h>
  21 #include <netinet/ip6.h>
  22 #include <sys/param.h>
  23
  24
  25 static void
  26 add_pad (struct cmsghdr *cmsg, int len)
  27 {
  28   unsigned char *p = CMSG_DATA (cmsg) + cmsg->cmsg_len - CMSG_LEN (0);
  29
  30   if (len == 1)
  31     /* Special handling for 1, a one-byte solution.  */
  32     *p++ = IP6OPT_PAD1;
  33   else if (len != 0)
  34     {
  35       /* Multibyte padding.  */
  36       *p++ = IP6OPT_PADN;
  37       *p++ = len - 2;   /* Discount the two header bytes.  */
  38       /* The rest is filled with zero.  */
  39       memset (p, '\0', len - 2);
  40       p += len - 2;
  41     }
  42
  43   /* Account for the bytes.  */
  44   cmsg->cmsg_len += len;
  45 }
  46
  47
  48 static int
  49 get_opt_end (const uint8_t **result, const uint8_t *startp,
  50              const uint8_t *endp)
  51 {
  52   if (startp >= endp)
  53     /* Out of bounds.  */
  54     return -1;
  55
  56   if (*startp == IP6OPT_PAD1)
  57     {
  58       /* Just this one byte.  */
  59       *result = startp + 1;
  60       return 0;
  61     }
  62
  63   /* Now we know there must be at least two bytes.  */
  64   if (startp + 2 > endp
  65       /* Now we can get the length byte.  */
  66       || startp + startp[1] + 2 > endp)
  67     return -1;
  68
  69   *result = startp + startp[1] + 2;
  70
  71   return 0;
  72 }
  73
  74
  75 static uint8_t *option_alloc (struct cmsghdr *cmsg, int datalen, int multx,
  76                               int plusy);
  77
  78
  79 /* RFC 2292, 6.3.1
  80
  81    This function returns the number of bytes required to hold an option
  82    when it is stored as ancillary data, including the cmsghdr structure
  83    at the beginning, and any padding at the end (to make its size a
  84    multiple of 8 bytes).  The argument is the size of the structure
  85    defining the option, which must include any pad bytes at the
  86    beginning (the value y in the alignment term "xn + y"), the type
  87    byte, the length byte, and the option data.  */
  88 int
  89 inet6_option_space (int nbytes)
  90 {
  91   /* Add room for the extension header.  */
  92   nbytes += sizeof (struct ip6_ext);
  93
  94   return CMSG_SPACE (roundup (nbytes, 8));
  95 }
  96 link_warning (inet6_option_space,
  97               "inet6_option_space is obsolete, use the RFC 3542 interfaces")
  98
  99
 100 /* RFC 2292, 6.3.2
 101
 102    This function is called once per ancillary data object that will
 103    contain either Hop-by-Hop or Destination options.  It returns 0 on
 104    success or -1 on an error.  */
 105 int
 106 inet6_option_init (void *bp, struct cmsghdr **cmsgp, int type)
 107 {
 108   /* Only Hop-by-Hop or Destination options allowed.  */
 109   if (type != IPV6_HOPOPTS && type != IPV6_DSTOPTS)
 110     return -1;
 111
 112   /* BP is a pointer to the previously allocated space.  */
 113   struct cmsghdr *newp = (struct cmsghdr *) bp;
 114
 115   /* Initialize the message header.
 116
 117      Length: No data yet, only the cmsghdr struct.  */
 118   newp->cmsg_len = CMSG_LEN (0);
 119   /* Originating protocol: obviously IPv6.  */
 120   newp->cmsg_level = IPPROTO_IPV6;
 121   /* Message type.  */
 122   newp->cmsg_type = type;
 123
 124   /* Pass up the result.  */
 125   *cmsgp = newp;
 126
 127   return 0;
 128 }
 129 link_warning (inet6_option_init,
 130               "inet6_option_init is obsolete, use the RFC 3542 interfaces")
 131
 132
 133 /* RFC 2292, 6.3.3
 134
 135    This function appends a Hop-by-Hop option or a Destination option
 136    into an ancillary data object that has been initialized by
 137    inet6_option_init().  This function returns 0 if it succeeds or -1 on
 138    an error.  */
 139 int
 140 inet6_option_append (struct cmsghdr *cmsg, const uint8_t *typep, int multx,
 141                      int plusy)
 142 {
 143   /* typep is a pointer to the 8-bit option type.  It is assumed that this
 144      field is immediately followed by the 8-bit option data length field,
 145      which is then followed immediately by the option data.
 146
 147      The option types IP6OPT_PAD1 and IP6OPT_PADN also must be handled.  */
 148   int len = typep[0] == IP6OPT_PAD1 ? 1 : typep[1] + 2;
 149
 150   /* Get the pointer to the space in the message.  */
 151   uint8_t *ptr = option_alloc (cmsg, len, multx, plusy);
 152   if (ptr == NULL)
 153     /* Some problem with the parameters.  */
 154     return -1;
 155
 156   /* Copy the content.  */
 157   memcpy (ptr, typep, len);
 158
 159   return 0;
 160 }
 161 link_warning (inet6_option_append,
 162               "inet6_option_append is obsolete, use the RFC 3542 interfaces")
 163
 164
 165 /* RFC 2292, 6.3.4
 166
 167    This function appends a Hop-by-Hop option or a Destination option
 168    into an ancillary data object that has been initialized by
 169    inet6_option_init().  This function returns a pointer to the 8-bit
 170    option type field that starts the option on success, or NULL on an
 171    error.  */
 172 static uint8_t *
 173 option_alloc (struct cmsghdr *cmsg, int datalen, int multx, int plusy)
 174 {
 175   /* The RFC limits the value of the alignment values.  */
 176   if ((multx != 1 && multx != 2 && multx != 4 && multx != 8)
 177       || ! (plusy >= 0 && plusy <= 7))
 178     return NULL;
 179
 180   /* Current data size.  */
 181   int dsize = cmsg->cmsg_len - CMSG_LEN (0);
 182
 183   /* The first two bytes of the option are for the extended header.  */
 184   if (__glibc_unlikely (dsize == 0))
 185     {
 186       cmsg->cmsg_len += sizeof (struct ip6_ext);
 187       dsize = sizeof (struct ip6_ext);
 188     }
 189
 190   /* First add padding.  */
 191   add_pad (cmsg, ((multx - (dsize & (multx - 1))) & (multx - 1)) + plusy);
 192
 193   /* Return the pointer to the start of the option space.  */
 194   uint8_t *result = CMSG_DATA (cmsg) + cmsg->cmsg_len - CMSG_LEN (0);
 195   cmsg->cmsg_len += datalen;
 196
 197   /* The extended option header length is measured in 8-byte groups.
 198      To represent the current length we might have to add padding.  */
 199   dsize = cmsg->cmsg_len - CMSG_LEN (0);
 200   add_pad (cmsg, (8 - (dsize & (8 - 1))) & (8 - 1));
 201
 202   /* Record the new length of the option.  */
 203   assert (((cmsg->cmsg_len - CMSG_LEN (0)) % 8) == 0);
 204   int len8b = (cmsg->cmsg_len - CMSG_LEN (0)) / 8 - 1;
 205   if (len8b >= 256)
 206     /* Too long.  */
 207     return NULL;
 208
 209   struct ip6_ext *ie = (void *) CMSG_DATA (cmsg);
 210   ie->ip6e_len = len8b;
 211
 212   return result;
 213 }
 214
 215
 216 uint8_t *
 217 inet6_option_alloc (struct cmsghdr *cmsg, int datalen, int multx, int plusy)
 218 {
 219   return option_alloc (cmsg, datalen, multx, plusy);
 220 }
 221 link_warning (inet6_option_alloc,
 222               "inet6_option_alloc is obsolete, use the RFC 3542 interfaces")
 223
 224
 225 /* RFC 2292, 6.3.5
 226
 227    This function processes the next Hop-by-Hop option or Destination
 228    option in an ancillary data object.  If another option remains to be
 229    processed, the return value of the function is 0 and *tptrp points to
 230    the 8-bit option type field (which is followed by the 8-bit option
 231    data length, followed by the option data).  If no more options remain
 232    to be processed, the return value is -1 and *tptrp is NULL.  If an
 233    error occurs, the return value is -1 and *tptrp is not NULL.  */
 234 int
 235 inet6_option_next (const struct cmsghdr *cmsg, uint8_t **tptrp)
 236 {
 237   /* Make sure it is an option of the right type.  */
 238   if (cmsg->cmsg_level != IPPROTO_IPV6
 239       || (cmsg->cmsg_type != IPV6_HOPOPTS && cmsg->cmsg_type != IPV6_DSTOPTS))
 240     return -1;
 241
 242   /* Pointer to the extension header.  We only compute the address, we
 243      don't access anything yet.  */
 244   const struct ip6_ext *ip6e = (const struct ip6_ext *) CMSG_DATA (cmsg);
 245
 246   /* Make sure the message is long enough.  */
 247   if (cmsg->cmsg_len < CMSG_LEN (sizeof (struct ip6_ext))
 248       /* Now we can access the extension header.  */
 249       || cmsg->cmsg_len < CMSG_LEN ((ip6e->ip6e_len + 1) * 8))
 250     /* Too small.  */
 251     return -1;
 252
 253   /* Determine the address of the byte past the message.  */
 254   const uint8_t *endp = CMSG_DATA (cmsg) + (ip6e->ip6e_len + 1) * 8;
 255
 256   const uint8_t *result;
 257   if (*tptrp == NULL)
 258     /* This is the first call, return the first option if there is one.  */
 259     result = (const uint8_t *) (ip6e + 1);
 260   else
 261     {
 262       /* Make sure *TPTRP points to a beginning of a new option in
 263          the message.  The upper limit is checked in get_opt_end.  */
 264       if (*tptrp < (const uint8_t *) (ip6e + 1))
 265         return -1;
 266
 267       /* Get the beginning of the next option.  */
 268       if (get_opt_end (&result, *tptrp, endp) != 0)
 269         return -1;
 270     }
 271
 272   /* We know where the next option starts.  */
 273   *tptrp = (uint8_t *) result;
 274
 275   /* Check the option is fully represented in the message.  */
 276   return get_opt_end (&result, result, endp);
 277 }
 278 link_warning (inet6_option_next,
 279               "inet6_option_next is obsolete, use the RFC 3542 interfaces")
 280
 281
 282 /* RFC 2292, 6.3.6
 283
 284    This function is similar to the previously described
 285    inet6_option_next() function, except this function lets the caller
 286    specify the option type to be searched for, instead of always
 287    returning the next option in the ancillary data object.  cmsg is a
 288    pointer to cmsghdr structure of which cmsg_level equals IPPROTO_IPV6
 289    and cmsg_type equals either IPV6_HOPOPTS or IPV6_DSTOPTS.  */
 290 int
 291 inet6_option_find (const struct cmsghdr *cmsg, uint8_t **tptrp, int type)
 292 {
 293   /* Make sure it is an option of the right type.  */
 294   if (cmsg->cmsg_level != IPPROTO_IPV6
 295       || (cmsg->cmsg_type != IPV6_HOPOPTS && cmsg->cmsg_type != IPV6_DSTOPTS))
 296     return -1;
 297
 298   /* Pointer to the extension header.  We only compute the address, we
 299      don't access anything yet.  */
 300   const struct ip6_ext *ip6e = (const struct ip6_ext *) CMSG_DATA (cmsg);
 301
 302   /* Make sure the message is long enough.  */
 303   if (cmsg->cmsg_len < CMSG_LEN (sizeof (struct ip6_ext))
 304       /* Now we can access the extension header.  */
 305       || cmsg->cmsg_len < CMSG_LEN ((ip6e->ip6e_len + 1) * 8))
 306     /* Too small.  */
 307     return -1;
 308
 309   /* Determine the address of the byte past the message.  */
 310   const uint8_t *endp = CMSG_DATA (cmsg) + (ip6e->ip6e_len + 1) * 8;
 311
 312   const uint8_t *next;
 313   if (*tptrp == NULL)
 314     /* This is the first call, return the first option if there is one.  */
 315     next = (const uint8_t *) (ip6e + 1);
 316   else
 317     {
 318       /* Make sure *TPTRP points to a beginning of a new option in
 319          the message.  The upper limit is checked in get_opt_end.  */
 320       if (*tptrp < (const uint8_t *) (ip6e + 1))
 321         return -1;
 322
 323       /* Get the beginning of the next option.  */
 324       if (get_opt_end (&next, *tptrp, endp) != 0)
 325         return -1;
 326     }
 327
 328   /* Now search for the appropriate typed entry.  */
 329   const uint8_t *result;
 330   do
 331     {
 332       result = next;
 333
 334       /* Get the end of this entry.  */
 335       if (get_opt_end (&next, result, endp) != 0)
 336         return -1;
 337     }
 338   while (*result != type);
 339
 340   /* We know where the next option starts.  */
 341   *tptrp = (uint8_t *) result;
 342
 343   /* Success.  */
 344   return 0;
 345 }
 346 link_warning (inet6_option_find,
 347               "inet6_option_find is obsolete, use the RFC 3542 interfaces")