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 /*
 116  * find the offset to specified header or the protocol number of last header
 117  * if target < 0. "last header" is transport protocol header, ESP, or
 118  * "No next header".
 119  *
 120  * Note that *offset is used as input/output parameter. an if it is not zero,
 121  * then it must be a valid offset to an inner IPv6 header. This can be used
 122  * to explore inner IPv6 header, eg. ICMPv6 error messages.
 123  *
 124  * If target header is found, its offset is set in *offset and return protocol
 125  * number. Otherwise, return -1.
 126  *
 127  * If the first fragment doesn't contain the final protocol header or
 128  * NEXTHDR_NONE it is considered invalid.
 129  *
 130  * Note that non-1st fragment is special case that "the protocol number
 131  * of last header" is "next header" field in Fragment header. In this case,
 132  * *offset is meaningless and fragment offset is stored in *fragoff if fragoff
 133  * isn't NULL.
 134  *
 135  * if flags is not NULL and it's a fragment, then the frag flag IP6_FH_F_FRAG
 136  * will be set. If it's an AH header, the IP6_FH_F_AUTH flag is set and
 137  * target < 0, then this function will stop at the AH header.
 138  */
 139 int ipv6_find_hdr(const struct sk_buff *skb, unsigned int *offset,
 140                   int target, unsigned short *fragoff, int *flags)
 141 {
 142         unsigned int start = skb_network_offset(skb) + sizeof(struct ipv6hdr);
 143         u8 nexthdr = ipv6_hdr(skb)->nexthdr;
 144         unsigned int len;
 145
 146         if (fragoff)
 147                 *fragoff = 0;
 148
 149         if (*offset) {
 150                 struct ipv6hdr _ip6, *ip6;
 151
 152                 ip6 = skb_header_pointer(skb, *offset, sizeof(_ip6), &_ip6);
 153                 if (!ip6 || (ip6->version != 6)) {
 154                         printk(KERN_ERR "IPv6 header not found\n");
 155                         return -EBADMSG;
 156                 }
 157                 start = *offset + sizeof(struct ipv6hdr);
 158                 nexthdr = ip6->nexthdr;
 159         }
 160         len = skb->len - start;
 161
 162         while (nexthdr != target) {
 163                 struct ipv6_opt_hdr _hdr, *hp;
 164                 unsigned int hdrlen;
 165
 166                 if ((!ipv6_ext_hdr(nexthdr)) || nexthdr == NEXTHDR_NONE) {
 167                         if (target < 0)
 168                                 break;
 169                         return -ENOENT;
 170                 }
 171
 172                 hp = skb_header_pointer(skb, start, sizeof(_hdr), &_hdr);
 173                 if (hp == NULL)
 174                         return -EBADMSG;
 175                 if (nexthdr == NEXTHDR_FRAGMENT) {
 176                         unsigned short _frag_off;
 177                         __be16 *fp;
 178
 179                         if (flags)      /* Indicate that this is a fragment */
 180                                 *flags |= IP6_FH_F_FRAG;
 181                         fp = skb_header_pointer(skb,
 182                                                 start+offsetof(struct frag_hdr,
 183                                                                frag_off),
 184                                                 sizeof(_frag_off),
 185                                                 &_frag_off);
 186                         if (fp == NULL)
 187                                 return -EBADMSG;
 188
 189                         _frag_off = ntohs(*fp) & ~0x7;
 190                         if (_frag_off) {
 191                                 if (target < 0 &&
 192                                     ((!ipv6_ext_hdr(hp->nexthdr)) ||
 193                                      hp->nexthdr == NEXTHDR_NONE)) {
 194                                         if (fragoff)
 195                                                 *fragoff = _frag_off;
 196                                         return hp->nexthdr;
 197                                 }
 198                                 return -ENOENT;
 199                         }
 200                         hdrlen = 8;
 201                 } else if (nexthdr == NEXTHDR_AUTH) {
 202                         if (flags && (*flags & IP6_FH_F_AUTH) && (target < 0))
 203                                 break;
 204                         hdrlen = (hp->hdrlen + 2) << 2;
 205                 } else
 206                         hdrlen = ipv6_optlen(hp);
 207
 208                 nexthdr = hp->nexthdr;
 209                 len -= hdrlen;
 210                 start += hdrlen;
 211         }
 212
 213         *offset = start;
 214         return nexthdr;
 215 }
 216 EXPORT_SYMBOL(ipv6_find_hdr);