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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 
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 }
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 }