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Linux/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 bool 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 EXPORT_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 
 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)
 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)
 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 }
113 EXPORT_SYMBOL(ipv6_skip_exthdr);
114 
115 int ipv6_find_tlv(const struct sk_buff *skb, int offset, int type)
116 {
117         const unsigned char *nh = skb_network_header(skb);
118         int packet_len = skb_tail_pointer(skb) - skb_network_header(skb);
119         struct ipv6_opt_hdr *hdr;
120         int len;
121 
122         if (offset + 2 > packet_len)
123                 goto bad;
124         hdr = (struct ipv6_opt_hdr *)(nh + offset);
125         len = ((hdr->hdrlen + 1) << 3);
126 
127         if (offset + len > packet_len)
128                 goto bad;
129 
130         offset += 2;
131         len -= 2;
132 
133         while (len > 0) {
134                 int opttype = nh[offset];
135                 int optlen;
136 
137                 if (opttype == type)
138                         return offset;
139 
140                 switch (opttype) {
141                 case IPV6_TLV_PAD1:
142                         optlen = 1;
143                         break;
144                 default:
145                         optlen = nh[offset + 1] + 2;
146                         if (optlen > len)
147                                 goto bad;
148                         break;
149                 }
150                 offset += optlen;
151                 len -= optlen;
152         }
153         /* not_found */
154  bad:
155         return -1;
156 }
157 EXPORT_SYMBOL_GPL(ipv6_find_tlv);
158 
159 /*
160  * find the offset to specified header or the protocol number of last header
161  * if target < 0. "last header" is transport protocol header, ESP, or
162  * "No next header".
163  *
164  * Note that *offset is used as input/output parameter. an if it is not zero,
165  * then it must be a valid offset to an inner IPv6 header. This can be used
166  * to explore inner IPv6 header, eg. ICMPv6 error messages.
167  *
168  * If target header is found, its offset is set in *offset and return protocol
169  * number. Otherwise, return -1.
170  *
171  * If the first fragment doesn't contain the final protocol header or
172  * NEXTHDR_NONE it is considered invalid.
173  *
174  * Note that non-1st fragment is special case that "the protocol number
175  * of last header" is "next header" field in Fragment header. In this case,
176  * *offset is meaningless and fragment offset is stored in *fragoff if fragoff
177  * isn't NULL.
178  *
179  * if flags is not NULL and it's a fragment, then the frag flag
180  * IP6_FH_F_FRAG will be set. If it's an AH header, the
181  * IP6_FH_F_AUTH flag is set and target < 0, then this function will
182  * stop at the AH header. If IP6_FH_F_SKIP_RH flag was passed, then this
183  * function will skip all those routing headers, where segements_left was 0.
184  */
185 int ipv6_find_hdr(const struct sk_buff *skb, unsigned int *offset,
186                   int target, unsigned short *fragoff, int *flags)
187 {
188         unsigned int start = skb_network_offset(skb) + sizeof(struct ipv6hdr);
189         u8 nexthdr = ipv6_hdr(skb)->nexthdr;
190         unsigned int len;
191         bool found;
192 
193         if (fragoff)
194                 *fragoff = 0;
195 
196         if (*offset) {
197                 struct ipv6hdr _ip6, *ip6;
198 
199                 ip6 = skb_header_pointer(skb, *offset, sizeof(_ip6), &_ip6);
200                 if (!ip6 || (ip6->version != 6)) {
201                         printk(KERN_ERR "IPv6 header not found\n");
202                         return -EBADMSG;
203                 }
204                 start = *offset + sizeof(struct ipv6hdr);
205                 nexthdr = ip6->nexthdr;
206         }
207         len = skb->len - start;
208 
209         do {
210                 struct ipv6_opt_hdr _hdr, *hp;
211                 unsigned int hdrlen;
212                 found = (nexthdr == target);
213 
214                 if ((!ipv6_ext_hdr(nexthdr)) || nexthdr == NEXTHDR_NONE) {
215                         if (target < 0 || found)
216                                 break;
217                         return -ENOENT;
218                 }
219 
220                 hp = skb_header_pointer(skb, start, sizeof(_hdr), &_hdr);
221                 if (!hp)
222                         return -EBADMSG;
223 
224                 if (nexthdr == NEXTHDR_ROUTING) {
225                         struct ipv6_rt_hdr _rh, *rh;
226 
227                         rh = skb_header_pointer(skb, start, sizeof(_rh),
228                                                 &_rh);
229                         if (!rh)
230                                 return -EBADMSG;
231 
232                         if (flags && (*flags & IP6_FH_F_SKIP_RH) &&
233                             rh->segments_left == 0)
234                                 found = false;
235                 }
236 
237                 if (nexthdr == NEXTHDR_FRAGMENT) {
238                         unsigned short _frag_off;
239                         __be16 *fp;
240 
241                         if (flags)      /* Indicate that this is a fragment */
242                                 *flags |= IP6_FH_F_FRAG;
243                         fp = skb_header_pointer(skb,
244                                                 start+offsetof(struct frag_hdr,
245                                                                frag_off),
246                                                 sizeof(_frag_off),
247                                                 &_frag_off);
248                         if (!fp)
249                                 return -EBADMSG;
250 
251                         _frag_off = ntohs(*fp) & ~0x7;
252                         if (_frag_off) {
253                                 if (target < 0 &&
254                                     ((!ipv6_ext_hdr(hp->nexthdr)) ||
255                                      hp->nexthdr == NEXTHDR_NONE)) {
256                                         if (fragoff)
257                                                 *fragoff = _frag_off;
258                                         return hp->nexthdr;
259                                 }
260                                 if (!found)
261                                         return -ENOENT;
262                                 if (fragoff)
263                                         *fragoff = _frag_off;
264                                 break;
265                         }
266                         hdrlen = 8;
267                 } else if (nexthdr == NEXTHDR_AUTH) {
268                         if (flags && (*flags & IP6_FH_F_AUTH) && (target < 0))
269                                 break;
270                         hdrlen = (hp->hdrlen + 2) << 2;
271                 } else
272                         hdrlen = ipv6_optlen(hp);
273 
274                 if (!found) {
275                         nexthdr = hp->nexthdr;
276                         len -= hdrlen;
277                         start += hdrlen;
278                 }
279         } while (!found);
280 
281         *offset = start;
282         return nexthdr;
283 }
284 EXPORT_SYMBOL(ipv6_find_hdr);
285 
286 

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