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 int 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
  25 /*
  26  * Skip any extension headers. This is used by the ICMP module.
  27  *
  28  * Note that strictly speaking this conflicts with RFC 2460 4.0:
  29  * ...The contents and semantics of each extension header determine whether
  30  * or not to proceed to the next header.  Therefore, extension headers must
  31  * be processed strictly in the order they appear in the packet; a
  32  * receiver must not, for example, scan through a packet looking for a
  33  * particular kind of extension header and process that header prior to
  34  * processing all preceding ones.
  35  *
  36  * We do exactly this. This is a protocol bug. We can't decide after a
  37  * seeing an unknown discard-with-error flavour TLV option if it's a
  38  * ICMP error message or not (errors should never be send in reply to
  39  * ICMP error messages).
  40  *
  41  * But I see no other way to do this. This might need to be reexamined
  42  * when Linux implements ESP (and maybe AUTH) headers.
  43  * --AK
  44  *
  45  * This function parses (probably truncated) exthdr set "hdr".
  46  * "nexthdrp" initially points to some place,
  47  * where type of the first header can be found.
  48  *
  49  * It skips all well-known exthdrs, and returns pointer to the start
  50  * of unparsable area i.e. the first header with unknown type.
  51  * If it is not NULL *nexthdr is updated by type/protocol of this header.
  52  *
  53  * NOTES: - if packet terminated with NEXTHDR_NONE it returns NULL.
  54  *        - it may return pointer pointing beyond end of packet,
  55  *          if the last recognized header is truncated in the middle.
  56  *        - if packet is truncated, so that all parsed headers are skipped,
  57  *          it returns NULL.
  58  *        - First fragment header is skipped, not-first ones
  59  *          are considered as unparsable.
  60  *        - Reports the offset field of the final fragment header so it is
  61  *          possible to tell whether this is a first fragment, later fragment,
  62  *          or not fragmented.
  63  *        - ESP is unparsable for now and considered like
  64  *          normal payload protocol.
  65  *        - Note also special handling of AUTH header. Thanks to IPsec wizards.
  66  *
  67  * --ANK (980726)
  68  */
  69
  70 int ipv6_skip_exthdr(const struct sk_buff *skb, int start, u8 *nexthdrp,
  71                      __be16 *frag_offp)
  72 {
  73         u8 nexthdr = *nexthdrp;
  74
  75         *frag_offp = 0;
  76
  77         while (ipv6_ext_hdr(nexthdr)) {
  78                 struct ipv6_opt_hdr _hdr, *hp;
  79                 int hdrlen;
  80
  81                 if (nexthdr == NEXTHDR_NONE)
  82                         return -1;
  83                 hp = skb_header_pointer(skb, start, sizeof(_hdr), &_hdr);
  84                 if (hp == NULL)
  85                         return -1;
  86                 if (nexthdr == NEXTHDR_FRAGMENT) {
  87                         __be16 _frag_off, *fp;
  88                         fp = skb_header_pointer(skb,
  89                                                 start+offsetof(struct frag_hdr,
  90                                                                frag_off),
  91                                                 sizeof(_frag_off),
  92                                                 &_frag_off);
  93                         if (fp == NULL)
  94                                 return -1;
  95
  96                         *frag_offp = *fp;
  97                         if (ntohs(*frag_offp) & ~0x7)
  98                                 break;
  99                         hdrlen = 8;
 100                 } else if (nexthdr == NEXTHDR_AUTH)
 101                         hdrlen = (hp->hdrlen+2)<<2;
 102                 else
 103                         hdrlen = ipv6_optlen(hp);
 104
 105                 nexthdr = hp->nexthdr;
 106                 start += hdrlen;
 107         }
 108
 109         *nexthdrp = nexthdr;
 110         return start;
 111 }
 112
 113 EXPORT_SYMBOL(ipv6_ext_hdr);
 114 EXPORT_SYMBOL(ipv6_skip_exthdr);