net/ipv6/exthdrs_core.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * IPv6 library code, needed by static components when full IPv6 support is
   4  * not configured or static.
   5  */
   6 #include <linux/export.h>
   7 #include <net/ipv6.h>
   8
   9 /*
  10  * find out if nexthdr is a well-known extension header or a protocol
  11  */
  12
  13 bool ipv6_ext_hdr(u8 nexthdr)
  14 {
  15         /*
  16          * find out if nexthdr is an extension header or a protocol
  17          */
  18         return   (nexthdr == NEXTHDR_HOP)       ||
  19                  (nexthdr == NEXTHDR_ROUTING)   ||
  20                  (nexthdr == NEXTHDR_FRAGMENT)  ||
  21                  (nexthdr == NEXTHDR_AUTH)      ||
  22                  (nexthdr == NEXTHDR_NONE)      ||
  23                  (nexthdr == NEXTHDR_DEST);
  24 }
  25 EXPORT_SYMBOL(ipv6_ext_hdr);
  26
  27 /*
  28  * Skip any extension headers. This is used by the ICMP module.
  29  *
  30  * Note that strictly speaking this conflicts with RFC 2460 4.0:
  31  * ...The contents and semantics of each extension header determine whether
  32  * or not to proceed to the next header.  Therefore, extension headers must
  33  * be processed strictly in the order they appear in the packet; a
  34  * receiver must not, for example, scan through a packet looking for a
  35  * particular kind of extension header and process that header prior to
  36  * processing all preceding ones.
  37  *
  38  * We do exactly this. This is a protocol bug. We can't decide after a
  39  * seeing an unknown discard-with-error flavour TLV option if it's a
  40  * ICMP error message or not (errors should never be send in reply to
  41  * ICMP error messages).
  42  *
  43  * But I see no other way to do this. This might need to be reexamined
  44  * when Linux implements ESP (and maybe AUTH) headers.
  45  * --AK
  46  *
  47  * This function parses (probably truncated) exthdr set "hdr".
  48  * "nexthdrp" initially points to some place,
  49  * where type of the first header can be found.
  50  *
  51  * It skips all well-known exthdrs, and returns pointer to the start
  52  * of unparsable area i.e. the first header with unknown type.
  53  * If it is not NULL *nexthdr is updated by type/protocol of this header.
  54  *
  55  * NOTES: - if packet terminated with NEXTHDR_NONE it returns NULL.
  56  *        - it may return pointer pointing beyond end of packet,
  57  *          if the last recognized header is truncated in the middle.
  58  *        - if packet is truncated, so that all parsed headers are skipped,
  59  *          it returns NULL.
  60  *        - First fragment header is skipped, not-first ones
  61  *          are considered as unparsable.
  62  *        - Reports the offset field of the final fragment header so it is
  63  *          possible to tell whether this is a first fragment, later fragment,
  64  *          or not fragmented.
  65  *        - ESP is unparsable for now and considered like
  66  *          normal payload protocol.
  67  *        - Note also special handling of AUTH header. Thanks to IPsec wizards.
  68  *
  69  * --ANK (980726)
  70  */
  71
  72 int ipv6_skip_exthdr(const struct sk_buff *skb, int start, u8 *nexthdrp,
  73                      __be16 *frag_offp)
  74 {
  75         u8 nexthdr = *nexthdrp;
  76
  77         *frag_offp = 0;
  78
  79         while (ipv6_ext_hdr(nexthdr)) {
  80                 struct ipv6_opt_hdr _hdr, *hp;
  81                 int hdrlen;
  82
  83                 if (nexthdr == NEXTHDR_NONE)
  84                         return -1;
  85                 hp = skb_header_pointer(skb, start, sizeof(_hdr), &_hdr);
  86                 if (!hp)
  87                         return -1;
  88                 if (nexthdr == NEXTHDR_FRAGMENT) {
  89                         __be16 _frag_off, *fp;
  90                         fp = skb_header_pointer(skb,
  91                                                 start+offsetof(struct frag_hdr,
  92                                                                frag_off),
  93                                                 sizeof(_frag_off),
  94                                                 &_frag_off);
  95                         if (!fp)
  96                                 return -1;
  97
  98                         *frag_offp = *fp;
  99                         if (ntohs(*frag_offp) & ~0x7)
 100                                 break;
 101                         hdrlen = 8;
 102                 } else if (nexthdr == NEXTHDR_AUTH)
 103                         hdrlen = ipv6_authlen(hp);
 104                 else
 105                         hdrlen = ipv6_optlen(hp);
 106
 107                 nexthdr = hp->nexthdr;
 108                 start += hdrlen;
 109         }
 110
 111         *nexthdrp = nexthdr;
 112         return start;
 113 }
 114 EXPORT_SYMBOL(ipv6_skip_exthdr);
 115
 116 int ipv6_find_tlv(const struct sk_buff *skb, int offset, int type)
 117 {
 118         const unsigned char *nh = skb_network_header(skb);
 119         int packet_len = skb_tail_pointer(skb) - skb_network_header(skb);
 120         struct ipv6_opt_hdr *hdr;
 121         int len;
 122
 123         if (offset + 2 > packet_len)
 124                 goto bad;
 125         hdr = (struct ipv6_opt_hdr *)(nh + offset);
 126         len = ((hdr->hdrlen + 1) << 3);
 127
 128         if (offset + len > packet_len)
 129                 goto bad;
 130
 131         offset += 2;
 132         len -= 2;
 133
 134         while (len > 0) {
 135                 int opttype = nh[offset];
 136                 int optlen;
 137
 138                 if (opttype == type)
 139                         return offset;
 140
 141                 switch (opttype) {
 142                 case IPV6_TLV_PAD1:
 143                         optlen = 1;
 144                         break;
 145                 default:
 146                         optlen = nh[offset + 1] + 2;
 147                         if (optlen > len)
 148                                 goto bad;
 149                         break;
 150                 }
 151                 offset += optlen;
 152                 len -= optlen;
 153         }
 154         /* not_found */
 155  bad:
 156         return -1;
 157 }
 158 EXPORT_SYMBOL_GPL(ipv6_find_tlv);
 159
 160 /*
 161  * find the offset to specified header or the protocol number of last header
 162  * if target < 0. "last header" is transport protocol header, ESP, or
 163  * "No next header".
 164  *
 165  * Note that *offset is used as input/output parameter, and if it is not zero,
 166  * then it must be a valid offset to an inner IPv6 header. This can be used
 167  * to explore inner IPv6 header, eg. ICMPv6 error messages.
 168  *
 169  * If target header is found, its offset is set in *offset and return protocol
 170  * number. Otherwise, return -1.
 171  *
 172  * If the first fragment doesn't contain the final protocol header or
 173  * NEXTHDR_NONE it is considered invalid.
 174  *
 175  * Note that non-1st fragment is special case that "the protocol number
 176  * of last header" is "next header" field in Fragment header. In this case,
 177  * *offset is meaningless and fragment offset is stored in *fragoff if fragoff
 178  * isn't NULL.
 179  *
 180  * if flags is not NULL and it's a fragment, then the frag flag
 181  * IP6_FH_F_FRAG will be set. If it's an AH header, the
 182  * IP6_FH_F_AUTH flag is set and target < 0, then this function will
 183  * stop at the AH header. If IP6_FH_F_SKIP_RH flag was passed, then this
 184  * function will skip all those routing headers, where segements_left was 0.
 185  */
 186 int ipv6_find_hdr(const struct sk_buff *skb, unsigned int *offset,
 187                   int target, unsigned short *fragoff, int *flags)
 188 {
 189         unsigned int start = skb_network_offset(skb) + sizeof(struct ipv6hdr);
 190         u8 nexthdr = ipv6_hdr(skb)->nexthdr;
 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                         return -EBADMSG;
 202                 start = *offset + sizeof(struct ipv6hdr);
 203                 nexthdr = ip6->nexthdr;
 204         }
 205
 206         do {
 207                 struct ipv6_opt_hdr _hdr, *hp;
 208                 unsigned int hdrlen;
 209                 found = (nexthdr == target);
 210
 211                 if ((!ipv6_ext_hdr(nexthdr)) || nexthdr == NEXTHDR_NONE) {
 212                         if (target < 0 || found)
 213                                 break;
 214                         return -ENOENT;
 215                 }
 216
 217                 hp = skb_header_pointer(skb, start, sizeof(_hdr), &_hdr);
 218                 if (!hp)
 219                         return -EBADMSG;
 220
 221                 if (nexthdr == NEXTHDR_ROUTING) {
 222                         struct ipv6_rt_hdr _rh, *rh;
 223
 224                         rh = skb_header_pointer(skb, start, sizeof(_rh),
 225                                                 &_rh);
 226                         if (!rh)
 227                                 return -EBADMSG;
 228
 229                         if (flags && (*flags & IP6_FH_F_SKIP_RH) &&
 230                             rh->segments_left == 0)
 231                                 found = false;
 232                 }
 233
 234                 if (nexthdr == NEXTHDR_FRAGMENT) {
 235                         unsigned short _frag_off;
 236                         __be16 *fp;
 237
 238                         if (flags)      /* Indicate that this is a fragment */
 239                                 *flags |= IP6_FH_F_FRAG;
 240                         fp = skb_header_pointer(skb,
 241                                                 start+offsetof(struct frag_hdr,
 242                                                                frag_off),
 243                                                 sizeof(_frag_off),
 244                                                 &_frag_off);
 245                         if (!fp)
 246                                 return -EBADMSG;
 247
 248                         _frag_off = ntohs(*fp) & ~0x7;
 249                         if (_frag_off) {
 250                                 if (target < 0 &&
 251                                     ((!ipv6_ext_hdr(hp->nexthdr)) ||
 252                                      hp->nexthdr == NEXTHDR_NONE)) {
 253                                         if (fragoff)
 254                                                 *fragoff = _frag_off;
 255                                         return hp->nexthdr;
 256                                 }
 257                                 if (!found)
 258                                         return -ENOENT;
 259                                 if (fragoff)
 260                                         *fragoff = _frag_off;
 261                                 break;
 262                         }
 263                         hdrlen = 8;
 264                 } else if (nexthdr == NEXTHDR_AUTH) {
 265                         if (flags && (*flags & IP6_FH_F_AUTH) && (target < 0))
 266                                 break;
 267                         hdrlen = ipv6_authlen(hp);
 268                 } else
 269                         hdrlen = ipv6_optlen(hp);
 270
 271                 if (!found) {
 272                         nexthdr = hp->nexthdr;
 273                         start += hdrlen;
 274                 }
 275         } while (!found);
 276
 277         *offset = start;
 278         return nexthdr;
 279 }
 280 EXPORT_SYMBOL(ipv6_find_hdr);