net/ipv6/exthdrs_core.c

   1 /*
   2  * IPv6 library code, needed by static components when full IPv6 support is
   3  * not configured or static.
   4  */
   5 #include <linux/export.h>
   6 #include <net/ipv6.h>
   7
   8 /*
   9  * find out if nexthdr is a well-known extension header or a protocol
  10  */
  11
  12 bool ipv6_ext_hdr(u8 nexthdr)
  13 {
  14         /*
  15          * find out if nexthdr is an extension header or a protocol
  16          */
  17         return   (nexthdr == NEXTHDR_HOP)       ||
  18                  (nexthdr == NEXTHDR_ROUTING)   ||
  19                  (nexthdr == NEXTHDR_FRAGMENT)  ||
  20                  (nexthdr == NEXTHDR_AUTH)      ||
  21                  (nexthdr == NEXTHDR_NONE)      ||
  22                  (nexthdr == NEXTHDR_DEST);
  23 }
  24 EXPORT_SYMBOL(ipv6_ext_hdr);
  25
  26 /*
  27  * Skip any extension headers. This is used by the ICMP module.
  28  *
  29  * Note that strictly speaking this conflicts with RFC 2460 4.0:
  30  * ...The contents and semantics of each extension header determine whether
  31  * or not to proceed to the next header.  Therefore, extension headers must
  32  * be processed strictly in the order they appear in the packet; a
  33  * receiver must not, for example, scan through a packet looking for a
  34  * particular kind of extension header and process that header prior to
  35  * processing all preceding ones.
  36  *
  37  * We do exactly this. This is a protocol bug. We can't decide after a
  38  * seeing an unknown discard-with-error flavour TLV option if it's a
  39  * ICMP error message or not (errors should never be send in reply to
  40  * ICMP error messages).
  41  *
  42  * But I see no other way to do this. This might need to be reexamined
  43  * when Linux implements ESP (and maybe AUTH) headers.
  44  * --AK
  45  *
  46  * This function parses (probably truncated) exthdr set "hdr".
  47  * "nexthdrp" initially points to some place,
  48  * where type of the first header can be found.
  49  *
  50  * It skips all well-known exthdrs, and returns pointer to the start
  51  * of unparsable area i.e. the first header with unknown type.
  52  * If it is not NULL *nexthdr is updated by type/protocol of this header.
  53  *
  54  * NOTES: - if packet terminated with NEXTHDR_NONE it returns NULL.
  55  *        - it may return pointer pointing beyond end of packet,
  56  *          if the last recognized header is truncated in the middle.
  57  *        - if packet is truncated, so that all parsed headers are skipped,
  58  *          it returns NULL.
  59  *        - First fragment header is skipped, not-first ones
  60  *          are considered as unparsable.
  61  *        - Reports the offset field of the final fragment header so it is
  62  *          possible to tell whether this is a first fragment, later fragment,
  63  *          or not fragmented.
  64  *        - ESP is unparsable for now and considered like
  65  *          normal payload protocol.
  66  *        - Note also special handling of AUTH header. Thanks to IPsec wizards.
  67  *
  68  * --ANK (980726)
  69  */
  70
  71 int ipv6_skip_exthdr(const struct sk_buff *skb, int start, u8 *nexthdrp,
  72                      __be16 *frag_offp)
  73 {
  74         u8 nexthdr = *nexthdrp;
  75
  76         *frag_offp = 0;
  77
  78         while (ipv6_ext_hdr(nexthdr)) {
  79                 struct ipv6_opt_hdr _hdr, *hp;
  80                 int hdrlen;
  81
  82                 if (nexthdr == NEXTHDR_NONE)
  83                         return -1;
  84                 hp = skb_header_pointer(skb, start, sizeof(_hdr), &_hdr);
  85                 if (hp == NULL)
  86                         return -1;
  87                 if (nexthdr == NEXTHDR_FRAGMENT) {
  88                         __be16 _frag_off, *fp;
  89                         fp = skb_header_pointer(skb,
  90                                                 start+offsetof(struct frag_hdr,
  91                                                                frag_off),
  92                                                 sizeof(_frag_off),
  93                                                 &_frag_off);
  94                         if (fp == NULL)
  95                                 return -1;
  96
  97                         *frag_offp = *fp;
  98                         if (ntohs(*frag_offp) & ~0x7)
  99                                 break;
 100                         hdrlen = 8;
 101                 } else if (nexthdr == NEXTHDR_AUTH)
 102                         hdrlen = (hp->hdrlen+2)<<2;
 103                 else
 104                         hdrlen = ipv6_optlen(hp);
 105
 106                 nexthdr = hp->nexthdr;
 107                 start += hdrlen;
 108         }
 109
 110         *nexthdrp = nexthdr;
 111         return start;
 112 }
 113 EXPORT_SYMBOL(ipv6_skip_exthdr);
 114
 115 int ipv6_find_tlv(struct sk_buff *skb, int offset, int type)
 116 {
 117         const unsigned char *nh = skb_network_header(skb);
 118         int packet_len = skb->tail - skb->network_header;
 119         struct ipv6_opt_hdr *hdr;
 120         int len;
 121
 122         if (offset + 2 > packet_len)
 123                 goto bad;
 124         hdr = (struct ipv6_opt_hdr *)(nh + offset);
 125         len = ((hdr->hdrlen + 1) << 3);
 126
 127         if (offset + len > packet_len)
 128                 goto bad;
 129
 130         offset += 2;
 131         len -= 2;
 132
 133         while (len > 0) {
 134                 int opttype = nh[offset];
 135                 int optlen;
 136
 137                 if (opttype == type)
 138                         return offset;
 139
 140                 switch (opttype) {
 141                 case IPV6_TLV_PAD1:
 142                         optlen = 1;
 143                         break;
 144                 default:
 145                         optlen = nh[offset + 1] + 2;
 146                         if (optlen > len)
 147                                 goto bad;
 148                         break;
 149                 }
 150                 offset += optlen;
 151                 len -= optlen;
 152         }
 153         /* not_found */
 154  bad:
 155         return -1;
 156 }
 157 EXPORT_SYMBOL_GPL(ipv6_find_tlv);
 158
 159 /*
 160  * find the offset to specified header or the protocol number of last header
 161  * if target < 0. "last header" is transport protocol header, ESP, or
 162  * "No next header".
 163  *
 164  * Note that *offset is used as input/output parameter. an if it is not zero,
 165  * then it must be a valid offset to an inner IPv6 header. This can be used
 166  * to explore inner IPv6 header, eg. ICMPv6 error messages.
 167  *
 168  * If target header is found, its offset is set in *offset and return protocol
 169  * number. Otherwise, return -1.
 170  *
 171  * If the first fragment doesn't contain the final protocol header or
 172  * NEXTHDR_NONE it is considered invalid.
 173  *
 174  * Note that non-1st fragment is special case that "the protocol number
 175  * of last header" is "next header" field in Fragment header. In this case,
 176  * *offset is meaningless and fragment offset is stored in *fragoff if fragoff
 177  * isn't NULL.
 178  *
 179  * if flags is not NULL and it's a fragment, then the frag flag
 180  * IP6_FH_F_FRAG will be set. If it's an AH header, the
 181  * IP6_FH_F_AUTH flag is set and target < 0, then this function will
 182  * stop at the AH header. If IP6_FH_F_SKIP_RH flag was passed, then this
 183  * function will skip all those routing headers, where segements_left was 0.
 184  */
 185 int ipv6_find_hdr(const struct sk_buff *skb, unsigned int *offset,
 186                   int target, unsigned short *fragoff, int *flags)
 187 {
 188         unsigned int start = skb_network_offset(skb) + sizeof(struct ipv6hdr);
 189         u8 nexthdr = ipv6_hdr(skb)->nexthdr;
 190         unsigned int len;
 191         bool found;
 192
 193         if (fragoff)
 194                 *fragoff = 0;
 195
 196         if (*offset) {
 197                 struct ipv6hdr _ip6, *ip6;
 198
 199                 ip6 = skb_header_pointer(skb, *offset, sizeof(_ip6), &_ip6);
 200                 if (!ip6 || (ip6->version != 6)) {
 201                         printk(KERN_ERR "IPv6 header not found\n");
 202                         return -EBADMSG;
 203                 }
 204                 start = *offset + sizeof(struct ipv6hdr);
 205                 nexthdr = ip6->nexthdr;
 206         }
 207         len = skb->len - start;
 208
 209         do {
 210                 struct ipv6_opt_hdr _hdr, *hp;
 211                 unsigned int hdrlen;
 212                 found = (nexthdr == target);
 213
 214                 if ((!ipv6_ext_hdr(nexthdr)) || nexthdr == NEXTHDR_NONE) {
 215                         if (target < 0 || found)
 216                                 break;
 217                         return -ENOENT;
 218                 }
 219
 220                 hp = skb_header_pointer(skb, start, sizeof(_hdr), &_hdr);
 221                 if (hp == NULL)
 222                         return -EBADMSG;
 223
 224                 if (nexthdr == NEXTHDR_ROUTING) {
 225                         struct ipv6_rt_hdr _rh, *rh;
 226
 227                         rh = skb_header_pointer(skb, start, sizeof(_rh),
 228                                                 &_rh);
 229                         if (rh == NULL)
 230                                 return -EBADMSG;
 231
 232                         if (flags && (*flags & IP6_FH_F_SKIP_RH) &&
 233                             rh->segments_left == 0)
 234                                 found = false;
 235                 }
 236
 237                 if (nexthdr == NEXTHDR_FRAGMENT) {
 238                         unsigned short _frag_off;
 239                         __be16 *fp;
 240
 241                         if (flags)      /* Indicate that this is a fragment */
 242                                 *flags |= IP6_FH_F_FRAG;
 243                         fp = skb_header_pointer(skb,
 244                                                 start+offsetof(struct frag_hdr,
 245                                                                frag_off),
 246                                                 sizeof(_frag_off),
 247                                                 &_frag_off);
 248                         if (fp == NULL)
 249                                 return -EBADMSG;
 250
 251                         _frag_off = ntohs(*fp) & ~0x7;
 252                         if (_frag_off) {
 253                                 if (target < 0 &&
 254                                     ((!ipv6_ext_hdr(hp->nexthdr)) ||
 255                                      hp->nexthdr == NEXTHDR_NONE)) {
 256                                         if (fragoff)
 257                                                 *fragoff = _frag_off;
 258                                         return hp->nexthdr;
 259                                 }
 260                                 return -ENOENT;
 261                         }
 262                         hdrlen = 8;
 263                 } else if (nexthdr == NEXTHDR_AUTH) {
 264                         if (flags && (*flags & IP6_FH_F_AUTH) && (target < 0))
 265                                 break;
 266                         hdrlen = (hp->hdrlen + 2) << 2;
 267                 } else
 268                         hdrlen = ipv6_optlen(hp);
 269
 270                 if (!found) {
 271                         nexthdr = hp->nexthdr;
 272                         len -= hdrlen;
 273                         start += hdrlen;
 274                 }
 275         } while (!found);
 276
 277         *offset = start;
 278         return nexthdr;
 279 }
 280 EXPORT_SYMBOL(ipv6_find_hdr);
 281