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 <net/ipv6.h>
   6
   7 /*
   8  * find out if nexthdr is a well-known extension header or a protocol
   9  */
  10
  11 int ipv6_ext_hdr(u8 nexthdr)
  12 {
  13         /*
  14          * find out if nexthdr is an extension header or a protocol
  15          */
  16         return ( (nexthdr == NEXTHDR_HOP)       ||
  17                  (nexthdr == NEXTHDR_ROUTING)   ||
  18                  (nexthdr == NEXTHDR_FRAGMENT)  ||
  19                  (nexthdr == NEXTHDR_AUTH)      ||
  20                  (nexthdr == NEXTHDR_NONE)      ||
  21                  (nexthdr == NEXTHDR_DEST) );
  22 }
  23
  24 /*
  25  * Skip any extension headers. This is used by the ICMP module.
  26  *
  27  * Note that strictly speaking this conflicts with RFC 2460 4.0:
  28  * ...The contents and semantics of each extension header determine whether
  29  * or not to proceed to the next header.  Therefore, extension headers must
  30  * be processed strictly in the order they appear in the packet; a
  31  * receiver must not, for example, scan through a packet looking for a
  32  * particular kind of extension header and process that header prior to
  33  * processing all preceding ones.
  34  *
  35  * We do exactly this. This is a protocol bug. We can't decide after a
  36  * seeing an unknown discard-with-error flavour TLV option if it's a
  37  * ICMP error message or not (errors should never be send in reply to
  38  * ICMP error messages).
  39  *
  40  * But I see no other way to do this. This might need to be reexamined
  41  * when Linux implements ESP (and maybe AUTH) headers.
  42  * --AK
  43  *
  44  * This function parses (probably truncated) exthdr set "hdr"
  45  * of length "len". "nexthdrp" initially points to some place,
  46  * where type of the first header can be found.
  47  *
  48  * It skips all well-known exthdrs, and returns pointer to the start
  49  * of unparsable area i.e. the first header with unknown type.
  50  * If it is not NULL *nexthdr is updated by type/protocol of this header.
  51  *
  52  * NOTES: - if packet terminated with NEXTHDR_NONE it returns NULL.
  53  *        - it may return pointer pointing beyond end of packet,
  54  *          if the last recognized header is truncated in the middle.
  55  *        - if packet is truncated, so that all parsed headers are skipped,
  56  *          it returns NULL.
  57  *        - First fragment header is skipped, not-first ones
  58  *          are considered as unparsable.
  59  *        - ESP is unparsable for now and considered like
  60  *          normal payload protocol.
  61  *        - Note also special handling of AUTH header. Thanks to IPsec wizards.
  62  *
  63  * --ANK (980726)
  64  */
  65
  66 int ipv6_skip_exthdr(const struct sk_buff *skb, int start, u8 *nexthdrp, int len)
  67 {
  68         u8 nexthdr = *nexthdrp;
  69
  70         while (ipv6_ext_hdr(nexthdr)) {
  71                 struct ipv6_opt_hdr _hdr, *hp;
  72                 int hdrlen;
  73
  74                 if (len < (int)sizeof(struct ipv6_opt_hdr))
  75                         return -1;
  76                 if (nexthdr == NEXTHDR_NONE)
  77                         return -1;
  78                 hp = skb_header_pointer(skb, start, sizeof(_hdr), &_hdr);
  79                 if (hp == NULL)
  80                         BUG();
  81                 if (nexthdr == NEXTHDR_FRAGMENT) {
  82                         unsigned short _frag_off, *fp;
  83                         fp = skb_header_pointer(skb,
  84                                                 start+offsetof(struct frag_hdr,
  85                                                                frag_off),
  86                                                 sizeof(_frag_off),
  87                                                 &_frag_off);
  88                         if (fp == NULL)
  89                                 return -1;
  90
  91                         if (ntohs(*fp) & ~0x7)
  92                                 break;
  93                         hdrlen = 8;
  94                 } else if (nexthdr == NEXTHDR_AUTH)
  95                         hdrlen = (hp->hdrlen+2)<<2;
  96                 else
  97                         hdrlen = ipv6_optlen(hp);
  98
  99                 nexthdr = hp->nexthdr;
 100                 len -= hdrlen;
 101                 start += hdrlen;
 102         }
 103
 104         *nexthdrp = nexthdr;
 105         return start;
 106 }
 107
 108 EXPORT_SYMBOL(ipv6_ext_hdr);
 109 EXPORT_SYMBOL(ipv6_skip_exthdr);