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
ipv6_ext_hdr(u8 nexthdr)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
ipv6_skip_exthdr(const struct sk_buff * skb,int start,u8 * nexthdrp,__be16 * frag_offp)72 int ipv6_skip_exthdr(const struct sk_buff *skb, int start, u8 *nexthdrp,
73 __be16 *frag_offp)
74 {
75 u8 nexthdr = *nexthdrp;
76 int exthdr_cnt = 0;
77
78 *frag_offp = 0;
79
80 while (ipv6_ext_hdr(nexthdr)) {
81 struct ipv6_opt_hdr _hdr, *hp;
82 int hdrlen;
83
84 if (nexthdr == NEXTHDR_NONE)
85 return -1;
86 if (unlikely(exthdr_cnt++ >= IP6_MAX_EXT_HDRS_CNT))
87 return -1;
88 hp = skb_header_pointer(skb, start, sizeof(_hdr), &_hdr);
89 if (!hp)
90 return -1;
91 if (nexthdr == NEXTHDR_FRAGMENT) {
92 __be16 _frag_off, *fp;
93 fp = skb_header_pointer(skb,
94 start+offsetof(struct frag_hdr,
95 frag_off),
96 sizeof(_frag_off),
97 &_frag_off);
98 if (!fp)
99 return -1;
100
101 *frag_offp = *fp;
102 if (ntohs(*frag_offp) & ~0x7)
103 break;
104 hdrlen = 8;
105 } else if (nexthdr == NEXTHDR_AUTH)
106 hdrlen = ipv6_authlen(hp);
107 else
108 hdrlen = ipv6_optlen(hp);
109
110 nexthdr = hp->nexthdr;
111 start += hdrlen;
112 }
113
114 *nexthdrp = nexthdr;
115 return start;
116 }
117 EXPORT_SYMBOL(ipv6_skip_exthdr);
118
ipv6_find_tlv(const struct sk_buff * skb,int offset,int type)119 int ipv6_find_tlv(const struct sk_buff *skb, int offset, int type)
120 {
121 const unsigned char *nh = skb_network_header(skb);
122 int packet_len = skb_tail_pointer(skb) - skb_network_header(skb);
123 struct ipv6_opt_hdr *hdr;
124 int len;
125
126 if (offset + 2 > packet_len)
127 goto bad;
128 hdr = (struct ipv6_opt_hdr *)(nh + offset);
129 len = ((hdr->hdrlen + 1) << 3);
130
131 if (offset + len > packet_len)
132 goto bad;
133
134 offset += 2;
135 len -= 2;
136
137 while (len > 0) {
138 int opttype = nh[offset];
139 int optlen;
140
141 if (opttype == type)
142 return offset;
143
144 switch (opttype) {
145 case IPV6_TLV_PAD1:
146 optlen = 1;
147 break;
148 default:
149 if (len < 2)
150 goto bad;
151 optlen = nh[offset + 1] + 2;
152 if (optlen > len)
153 goto bad;
154 break;
155 }
156 offset += optlen;
157 len -= optlen;
158 }
159 /* not_found */
160 bad:
161 return -1;
162 }
163 EXPORT_SYMBOL_GPL(ipv6_find_tlv);
164
165 /*
166 * find the offset to specified header or the protocol number of last header
167 * if target < 0. "last header" is transport protocol header, ESP, or
168 * "No next header".
169 *
170 * Note that *offset is used as input/output parameter, and if it is not zero,
171 * then it must be a valid offset to an inner IPv6 header. This can be used
172 * to explore inner IPv6 header, eg. ICMPv6 error messages.
173 *
174 * If target header is found, its offset is set in *offset and return protocol
175 * number. Otherwise, return -1.
176 *
177 * If the first fragment doesn't contain the final protocol header or
178 * NEXTHDR_NONE it is considered invalid.
179 *
180 * Note that non-1st fragment is special case that "the protocol number
181 * of last header" is "next header" field in Fragment header. In this case,
182 * *offset is meaningless and fragment offset is stored in *fragoff if fragoff
183 * isn't NULL.
184 *
185 * if flags is not NULL and it's a fragment, then the frag flag
186 * IP6_FH_F_FRAG will be set. If it's an AH header, the
187 * IP6_FH_F_AUTH flag is set and target < 0, then this function will
188 * stop at the AH header. If IP6_FH_F_SKIP_RH flag was passed, then this
189 * function will skip all those routing headers, where segements_left was 0.
190 */
ipv6_find_hdr(const struct sk_buff * skb,unsigned int * offset,int target,unsigned short * fragoff,int * flags)191 int ipv6_find_hdr(const struct sk_buff *skb, unsigned int *offset,
192 int target, unsigned short *fragoff, int *flags)
193 {
194 unsigned int start = skb_network_offset(skb) + sizeof(struct ipv6hdr);
195 u8 nexthdr = ipv6_hdr(skb)->nexthdr;
196 int exthdr_cnt = 0;
197 bool found;
198
199 if (fragoff)
200 *fragoff = 0;
201
202 if (*offset) {
203 struct ipv6hdr _ip6, *ip6;
204
205 ip6 = skb_header_pointer(skb, *offset, sizeof(_ip6), &_ip6);
206 if (!ip6 || (ip6->version != 6))
207 return -EBADMSG;
208 start = *offset + sizeof(struct ipv6hdr);
209 nexthdr = ip6->nexthdr;
210 }
211
212 do {
213 struct ipv6_opt_hdr _hdr, *hp;
214 unsigned int hdrlen;
215 found = (nexthdr == target);
216
217 if ((!ipv6_ext_hdr(nexthdr)) || nexthdr == NEXTHDR_NONE) {
218 if (target < 0 || found)
219 break;
220 return -ENOENT;
221 }
222
223 if (unlikely(exthdr_cnt++ >= IP6_MAX_EXT_HDRS_CNT))
224 return -EBADMSG;
225
226 hp = skb_header_pointer(skb, start, sizeof(_hdr), &_hdr);
227 if (!hp)
228 return -EBADMSG;
229
230 if (nexthdr == NEXTHDR_ROUTING) {
231 struct ipv6_rt_hdr _rh, *rh;
232
233 rh = skb_header_pointer(skb, start, sizeof(_rh),
234 &_rh);
235 if (!rh)
236 return -EBADMSG;
237
238 if (flags && (*flags & IP6_FH_F_SKIP_RH) &&
239 rh->segments_left == 0)
240 found = false;
241 }
242
243 if (nexthdr == NEXTHDR_FRAGMENT) {
244 unsigned short _frag_off;
245 __be16 *fp;
246
247 if (flags) /* Indicate that this is a fragment */
248 *flags |= IP6_FH_F_FRAG;
249 fp = skb_header_pointer(skb,
250 start+offsetof(struct frag_hdr,
251 frag_off),
252 sizeof(_frag_off),
253 &_frag_off);
254 if (!fp)
255 return -EBADMSG;
256
257 _frag_off = ntohs(*fp) & ~0x7;
258 if (_frag_off) {
259 if (target < 0 &&
260 ((!ipv6_ext_hdr(hp->nexthdr)) ||
261 hp->nexthdr == NEXTHDR_NONE)) {
262 if (fragoff)
263 *fragoff = _frag_off;
264 return hp->nexthdr;
265 }
266 if (!found)
267 return -ENOENT;
268 if (fragoff)
269 *fragoff = _frag_off;
270 break;
271 }
272 hdrlen = 8;
273 } else if (nexthdr == NEXTHDR_AUTH) {
274 if (flags && (*flags & IP6_FH_F_AUTH) && (target < 0))
275 break;
276 hdrlen = ipv6_authlen(hp);
277 } else
278 hdrlen = ipv6_optlen(hp);
279
280 if (!found) {
281 nexthdr = hp->nexthdr;
282 start += hdrlen;
283 }
284 } while (!found);
285
286 *offset = start;
287 return nexthdr;
288 }
289 EXPORT_SYMBOL(ipv6_find_hdr);
290