1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * IPv6 library code, needed by static components when full IPv6 support is
4 * not configured or static.
5 */
6 #include <linux/export.h>
7 #include <net/ipv6.h>
8
9 /*
10 * find out if nexthdr is a well-known extension header or a protocol
11 */
12
13 bool ipv6_ext_hdr(u8 nexthdr)
14 {
15 /*
16 * find out if nexthdr is an extension header or a protocol
17 */
18 return (nexthdr == NEXTHDR_HOP) ||
19 (nexthdr == NEXTHDR_ROUTING) ||
20 (nexthdr == NEXTHDR_FRAGMENT) ||
21 (nexthdr == NEXTHDR_AUTH) ||
22 (nexthdr == NEXTHDR_NONE) ||
23 (nexthdr == NEXTHDR_DEST);
24 }
25 EXPORT_SYMBOL(ipv6_ext_hdr);
26
27 /*
28 * Skip any extension headers. This is used by the ICMP module.
29 *
30 * Note that strictly speaking this conflicts with RFC 2460 4.0:
31 * ...The contents and semantics of each extension header determine whether
32 * or not to proceed to the next header. Therefore, extension headers must
33 * be processed strictly in the order they appear in the packet; a
34 * receiver must not, for example, scan through a packet looking for a
35 * particular kind of extension header and process that header prior to
36 * processing all preceding ones.
37 *
38 * We do exactly this. This is a protocol bug. We can't decide after a
39 * seeing an unknown discard-with-error flavour TLV option if it's a
40 * ICMP error message or not (errors should never be send in reply to
41 * ICMP error messages).
42 *
43 * But I see no other way to do this. This might need to be reexamined
44 * when Linux implements ESP (and maybe AUTH) headers.
45 * --AK
46 *
47 * This function parses (probably truncated) exthdr set "hdr".
48 * "nexthdrp" initially points to some place,
49 * where type of the first header can be found.
50 *
51 * It skips all well-known exthdrs, and returns pointer to the start
52 * of unparsable area i.e. the first header with unknown type.
53 * If it is not NULL *nexthdr is updated by type/protocol of this header.
54 *
55 * NOTES: - if packet terminated with NEXTHDR_NONE it returns NULL.
56 * - it may return pointer pointing beyond end of packet,
57 * if the last recognized header is truncated in the middle.
58 * - if packet is truncated, so that all parsed headers are skipped,
59 * it returns NULL.
60 * - First fragment header is skipped, not-first ones
61 * are considered as unparsable.
62 * - Reports the offset field of the final fragment header so it is
63 * possible to tell whether this is a first fragment, later fragment,
64 * or not fragmented.
65 * - ESP is unparsable for now and considered like
66 * normal payload protocol.
67 * - Note also special handling of AUTH header. Thanks to IPsec wizards.
68 *
69 * --ANK (980726)
70 */
71
72 int ipv6_skip_exthdr(const struct sk_buff *skb, int start, u8 *nexthdrp,
73 __be16 *frag_offp)
74 {
75 u8 nexthdr = *nexthdrp;
76
77 *frag_offp = 0;
78
79 while (ipv6_ext_hdr(nexthdr)) {
80 struct ipv6_opt_hdr _hdr, *hp;
81 int hdrlen;
82
83 if (nexthdr == NEXTHDR_NONE)
84 return -1;
85 hp = skb_header_pointer(skb, start, sizeof(_hdr), &_hdr);
86 if (!hp)
87 return -1;
88 if (nexthdr == NEXTHDR_FRAGMENT) {
89 __be16 _frag_off, *fp;
90 fp = skb_header_pointer(skb,
91 start+offsetof(struct frag_hdr,
92 frag_off),
93 sizeof(_frag_off),
94 &_frag_off);
95 if (!fp)
96 return -1;
97
98 *frag_offp = *fp;
99 if (ntohs(*frag_offp) & ~0x7)
100 break;
101 hdrlen = 8;
102 } else if (nexthdr == NEXTHDR_AUTH)
103 hdrlen = ipv6_authlen(hp);
104 else
105 hdrlen = ipv6_optlen(hp);
106
107 nexthdr = hp->nexthdr;
108 start += hdrlen;
109 }
110
111 *nexthdrp = nexthdr;
112 return start;
113 }
114 EXPORT_SYMBOL(ipv6_skip_exthdr);
115
116 int ipv6_find_tlv(const struct sk_buff *skb, int offset, int type)
117 {
118 const unsigned char *nh = skb_network_header(skb);
119 int packet_len = skb_tail_pointer(skb) - skb_network_header(skb);
120 struct ipv6_opt_hdr *hdr;
121 int len;
122
123 if (offset + 2 > packet_len)
124 goto bad;
125 hdr = (struct ipv6_opt_hdr *)(nh + offset);
126 len = ((hdr->hdrlen + 1) << 3);
127
128 if (offset + len > packet_len)
129 goto bad;
130
131 offset += 2;
132 len -= 2;
133
134 while (len > 0) {
135 int opttype = nh[offset];
136 int optlen;
137
138 if (opttype == type)
139 return offset;
140
141 switch (opttype) {
142 case IPV6_TLV_PAD1:
143 optlen = 1;
144 break;
145 default:
146 if (len < 2)
147 goto bad;
148 optlen = nh[offset + 1] + 2;
149 if (optlen > len)
150 goto bad;
151 break;
152 }
153 offset += optlen;
154 len -= optlen;
155 }
156 /* not_found */
157 bad:
158 return -1;
159 }
160 EXPORT_SYMBOL_GPL(ipv6_find_tlv);
161
162 /*
163 * find the offset to specified header or the protocol number of last header
164 * if target < 0. "last header" is transport protocol header, ESP, or
165 * "No next header".
166 *
167 * Note that *offset is used as input/output parameter, and if it is not zero,
168 * then it must be a valid offset to an inner IPv6 header. This can be used
169 * to explore inner IPv6 header, eg. ICMPv6 error messages.
170 *
171 * If target header is found, its offset is set in *offset and return protocol
172 * number. Otherwise, return -1.
173 *
174 * If the first fragment doesn't contain the final protocol header or
175 * NEXTHDR_NONE it is considered invalid.
176 *
177 * Note that non-1st fragment is special case that "the protocol number
178 * of last header" is "next header" field in Fragment header. In this case,
179 * *offset is meaningless and fragment offset is stored in *fragoff if fragoff
180 * isn't NULL.
181 *
182 * if flags is not NULL and it's a fragment, then the frag flag
183 * IP6_FH_F_FRAG will be set. If it's an AH header, the
184 * IP6_FH_F_AUTH flag is set and target < 0, then this function will
185 * stop at the AH header. If IP6_FH_F_SKIP_RH flag was passed, then this
186 * function will skip all those routing headers, where segements_left was 0.
187 */
188 int ipv6_find_hdr(const struct sk_buff *skb, unsigned int *offset,
189 int target, unsigned short *fragoff, int *flags)
190 {
191 unsigned int start = skb_network_offset(skb) + sizeof(struct ipv6hdr);
192 u8 nexthdr = ipv6_hdr(skb)->nexthdr;
193 bool found;
194
195 if (fragoff)
196 *fragoff = 0;
197
198 if (*offset) {
199 struct ipv6hdr _ip6, *ip6;
200
201 ip6 = skb_header_pointer(skb, *offset, sizeof(_ip6), &_ip6);
202 if (!ip6 || (ip6->version != 6))
203 return -EBADMSG;
204 start = *offset + sizeof(struct ipv6hdr);
205 nexthdr = ip6->nexthdr;
206 }
207
208 do {
209 struct ipv6_opt_hdr _hdr, *hp;
210 unsigned int hdrlen;
211 found = (nexthdr == target);
212
213 if ((!ipv6_ext_hdr(nexthdr)) || nexthdr == NEXTHDR_NONE) {
214 if (target < 0 || found)
215 break;
216 return -ENOENT;
217 }
218
219 hp = skb_header_pointer(skb, start, sizeof(_hdr), &_hdr);
220 if (!hp)
221 return -EBADMSG;
222
223 if (nexthdr == NEXTHDR_ROUTING) {
224 struct ipv6_rt_hdr _rh, *rh;
225
226 rh = skb_header_pointer(skb, start, sizeof(_rh),
227 &_rh);
228 if (!rh)
229 return -EBADMSG;
230
231 if (flags && (*flags & IP6_FH_F_SKIP_RH) &&
232 rh->segments_left == 0)
233 found = false;
234 }
235
236 if (nexthdr == NEXTHDR_FRAGMENT) {
237 unsigned short _frag_off;
238 __be16 *fp;
239
240 if (flags) /* Indicate that this is a fragment */
241 *flags |= IP6_FH_F_FRAG;
242 fp = skb_header_pointer(skb,
243 start+offsetof(struct frag_hdr,
244 frag_off),
245 sizeof(_frag_off),
246 &_frag_off);
247 if (!fp)
248 return -EBADMSG;
249
250 _frag_off = ntohs(*fp) & ~0x7;
251 if (_frag_off) {
252 if (target < 0 &&
253 ((!ipv6_ext_hdr(hp->nexthdr)) ||
254 hp->nexthdr == NEXTHDR_NONE)) {
255 if (fragoff)
256 *fragoff = _frag_off;
257 return hp->nexthdr;
258 }
259 if (!found)
260 return -ENOENT;
261 if (fragoff)
262 *fragoff = _frag_off;
263 break;
264 }
265 hdrlen = 8;
266 } else if (nexthdr == NEXTHDR_AUTH) {
267 if (flags && (*flags & IP6_FH_F_AUTH) && (target < 0))
268 break;
269 hdrlen = ipv6_authlen(hp);
270 } else
271 hdrlen = ipv6_optlen(hp);
272
273 if (!found) {
274 nexthdr = hp->nexthdr;
275 start += hdrlen;
276 }
277 } while (!found);
278
279 *offset = start;
280 return nexthdr;
281 }
282 EXPORT_SYMBOL(ipv6_find_hdr);
283
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