inet/inet6_opt.c

   1 /* Copyright (C) 2006-2024 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 <string.h>
  19 #include <netinet/in.h>
  20 #include <netinet/ip6.h>
  21
  22
  23 /* RFC 3542, 10.1
  24
  25    This function returns the number of bytes needed for the empty
  26    extension header i.e., without any options.  If EXTBUF is not NULL it
  27    also initializes the extension header to have the correct length
  28    field.  In that case if the EXTLEN value is not a positive (i.e.,
  29    non-zero) multiple of 8 the function fails and returns -1.  */
  30 int
  31 inet6_opt_init (void *extbuf, socklen_t extlen)
  32 {
  33   if (extbuf != NULL)
  34     {
  35       if (extlen <= 0 || (extlen % 8) != 0 || extlen > 256 * 8)
  36         return -1;
  37
  38       /* Fill in the length in units of 8 octets.  */
  39       struct ip6_hbh *extp = (struct ip6_hbh *) extbuf;
  40
  41       /* RFC 2460 requires that the header extension length is the
  42          length of the option header in 8-byte units, not including
  43          the first 8 bytes.  Hence we have to subtract one.  */
  44       extp->ip6h_len = extlen / 8 - 1;
  45     }
  46
  47   return sizeof (struct ip6_hbh);
  48 }
  49
  50
  51 static void
  52 add_padding (uint8_t *extbuf, int offset, int npad)
  53 {
  54   if (npad == 1)
  55     extbuf[offset] = IP6OPT_PAD1;
  56   else if (npad > 0)
  57     {
  58       struct ip6_opt *pad_opt = (struct ip6_opt *) (extbuf + offset);
  59
  60       pad_opt->ip6o_type = IP6OPT_PADN;
  61       pad_opt->ip6o_len = npad - sizeof (struct ip6_opt);
  62       /* Clear the memory used by the padding.  */
  63       memset (pad_opt + 1, '\0', pad_opt->ip6o_len);
  64     }
  65 }
  66
  67
  68
  69 /* RFC 3542, 10.2
  70
  71    This function returns the updated total length taking into account
  72    adding an option with length 'len' and alignment 'align'.  If
  73    EXTBUF is not NULL then, in addition to returning the length, the
  74    function inserts any needed pad option, initializes the option
  75    (setting the type and length fields) and returns a pointer to the
  76    location for the option content in databufp.  If the option does
  77    not fit in the extension header buffer the function returns -1.  */
  78 int
  79 inet6_opt_append (void *extbuf, socklen_t extlen, int offset, uint8_t type,
  80                   socklen_t len, uint8_t align, void **databufp)
  81 {
  82   /* Check minimum offset.  */
  83   if (offset < sizeof (struct ip6_hbh))
  84     return -1;
  85
  86   /* One cannot add padding options.  */
  87   if (type == IP6OPT_PAD1 || type == IP6OPT_PADN)
  88     return -1;
  89
  90   /* The option length must fit in one octet.  */
  91   if (len > 255)
  92     return -1;
  93
  94   /* The alignment can only by 1, 2, 4, or 8 and must not exceed the
  95      option length.  */
  96   if (align == 0 || align > 8 || (align & (align - 1)) != 0 || align > len)
  97     return -1;
  98
  99   /* Determine the needed padding for alignment.  Following the
 100      current content of the buffer we have the is the IPv6 option type
 101      and length, followed immediately by the data.  The data has the
 102      alignment constraints.  Therefore padding must be inserted in the
 103      form of padding options before the new option. */
 104   int data_offset = offset + sizeof (struct ip6_opt);
 105   int npad = (align - data_offset % align) & (align - 1);
 106
 107   if (extbuf != NULL)
 108     {
 109       /* Now we can check whether the buffer is large enough.  */
 110       if (data_offset + npad + len > extlen)
 111         return -1;
 112
 113       add_padding (extbuf, offset, npad);
 114
 115       offset += npad;
 116
 117       /* Now prepare the option itself.  */
 118       struct ip6_opt *opt = (struct ip6_opt *) ((uint8_t *) extbuf + offset);
 119
 120       opt->ip6o_type = type;
 121       opt->ip6o_len = len;
 122
 123       *databufp = opt + 1;
 124     }
 125   else
 126     offset += npad;
 127
 128   return offset + sizeof (struct ip6_opt) + len;
 129 }
 130
 131
 132 /* RFC 3542, 10.3
 133
 134    This function returns the updated total length taking into account
 135    the final padding of the extension header to make it a multiple of
 136    8 bytes.  If EXTBUF is not NULL the function also initializes the
 137    option by inserting a Pad1 or PadN option of the proper length.  */
 138 int
 139 inet6_opt_finish (void *extbuf, socklen_t extlen, int offset)
 140 {
 141   /* Check minimum offset.  */
 142   if (offset < sizeof (struct ip6_hbh))
 143     return -1;
 144
 145   /* Required padding at the end.  */
 146   int npad = (8 - (offset & 7)) & 7;
 147
 148   if (extbuf != NULL)
 149     {
 150       /* Make sure the buffer is large enough.  */
 151       if (offset + npad > extlen)
 152         return -1;
 153
 154       add_padding (extbuf, offset, npad);
 155     }
 156
 157   return offset + npad;
 158 }
 159
 160
 161 /* RFC 3542, 10.4
 162
 163    This function inserts data items of various sizes in the data
 164    portion of the option.  VAL should point to the data to be
 165    inserted.  OFFSET specifies where in the data portion of the option
 166    the value should be inserted; the first byte after the option type
 167    and length is accessed by specifying an offset of zero.  */
 168 int
 169 inet6_opt_set_val (void *databuf, int offset, void *val, socklen_t vallen)
 170 {
 171   memcpy ((uint8_t *) databuf + offset, val, vallen);
 172
 173   return offset + vallen;
 174 }
 175
 176
 177 /* RFC 3542, 10.5
 178
 179    This function parses received option extension headers returning
 180    the next option.  EXTBUF and EXTLEN specifies the extension header.
 181    OFFSET should either be zero (for the first option) or the length
 182    returned by a previous call to 'inet6_opt_next' or
 183    'inet6_opt_find'.  It specifies the position where to continue
 184    scanning the extension buffer.  */
 185 int
 186 inet6_opt_next (void *extbuf, socklen_t extlen, int offset, uint8_t *typep,
 187                 socklen_t *lenp, void **databufp)
 188 {
 189   if (offset == 0)
 190     offset = sizeof (struct ip6_hbh);
 191   else if (offset < sizeof (struct ip6_hbh))
 192     return -1;
 193
 194   while (offset < extlen)
 195     {
 196       struct ip6_opt *opt = (struct ip6_opt *) ((uint8_t *) extbuf + offset);
 197
 198       if (opt->ip6o_type == IP6OPT_PAD1)
 199         /* Single byte padding.  */
 200         ++offset;
 201       else if (opt->ip6o_type == IP6OPT_PADN)
 202         offset += sizeof (struct ip6_opt) + opt->ip6o_len;
 203       else
 204         {
 205           /* Check whether the option is valid.  */
 206           offset += sizeof (struct ip6_opt) + opt->ip6o_len;
 207           if (offset > extlen)
 208             return -1;
 209
 210           *typep = opt->ip6o_type;
 211           *lenp = opt->ip6o_len;
 212           *databufp = opt + 1;
 213           return offset;
 214         }
 215     }
 216
 217   return -1;
 218 }
 219
 220
 221 /* RFC 3542, 10.6
 222
 223    This function is similar to the previously described
 224    'inet6_opt_next' function, except this function lets the caller
 225    specify the option type to be searched for, instead of always
 226    returning the next option in the extension header.  */
 227 int
 228 inet6_opt_find (void *extbuf, socklen_t extlen, int offset, uint8_t type,
 229                 socklen_t *lenp, void **databufp)
 230 {
 231   if (offset == 0)
 232     offset = sizeof (struct ip6_hbh);
 233   else if (offset < sizeof (struct ip6_hbh))
 234     return -1;
 235
 236   while (offset < extlen)
 237     {
 238       struct ip6_opt *opt = (struct ip6_opt *) ((uint8_t *) extbuf + offset);
 239
 240       if (opt->ip6o_type == IP6OPT_PAD1)
 241         {
 242           /* Single byte padding.  */
 243           ++offset;
 244           if (type == IP6OPT_PAD1)
 245             {
 246               *lenp = 0;
 247               *databufp = (uint8_t *) extbuf + offset;
 248               return offset;
 249             }
 250         }
 251       else if (opt->ip6o_type != type)
 252         offset += sizeof (struct ip6_opt) + opt->ip6o_len;
 253       else
 254         {
 255           /* Check whether the option is valid.  */
 256           offset += sizeof (struct ip6_opt) + opt->ip6o_len;
 257           if (offset > extlen)
 258             return -1;
 259
 260           *lenp = opt->ip6o_len;
 261           *databufp = opt + 1;
 262           return offset;
 263         }
 264     }
 265
 266   return -1;
 267 }
 268
 269
 270 /* RFC 3542, 10.7
 271
 272    This function extracts data items of various sizes in the data
 273    portion of the option.  */
 274 int
 275 inet6_opt_get_val (void *databuf, int offset, void *val, socklen_t vallen)
 276 {
 277   memcpy (val, (uint8_t *) databuf + offset, vallen);
 278
 279   return offset + vallen;
 280 }