linux/net/ipv6/exthdrs_core.c
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   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
  12bool 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}
  24EXPORT_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
  71int 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}
 113EXPORT_SYMBOL(ipv6_skip_exthdr);
 114
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