LXR linux/net/ipv6/exthdrs

   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
  11int 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 * "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
  66int ipv6_skip_exthdr(const struct sk_buff *skb, int start, u8 *nexthdrp)
  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 (nexthdr == NEXTHDR_NONE)
  75                        return -1;
  76                hp = skb_header_pointer(skb, start, sizeof(_hdr), &_hdr);
  77                if (hp == NULL)
  78                        return -1;
  79                if (nexthdr == NEXTHDR_FRAGMENT) {
  80                        __be16 _frag_off, *fp;
  81                        fp = skb_header_pointer(skb,
  82                                                start+offsetof(struct frag_hdr,
  83                                                               frag_off),
  84                                                sizeof(_frag_off),
  85                                                &_frag_off);
  86                        if (fp == NULL)
  87                                return -1;
  88
  89                        if (ntohs(*fp) & ~0x7)
  90                                break;
  91                        hdrlen = 8;
  92                } else if (nexthdr == NEXTHDR_AUTH)
  93                        hdrlen = (hp->hdrlen+2)<<2;
  94                else
  95                        hdrlen = ipv6_optlen(hp);
  96
  97                nexthdr = hp->nexthdr;
  98                start += hdrlen;
  99        }
 100
 101        *nexthdrp = nexthdr;
 102        return start;
 103}
 104
 105EXPORT_SYMBOL(ipv6_ext_hdr);
 106EXPORT_SYMBOL(ipv6_skip_exthdr);
 107