xref: /openbmc/linux/net/ipv6/exthdrs_core.c (revision 878ecb08)
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 
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 
ipv6_find_tlv(const struct sk_buff * skb,int offset,int type)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  */
ipv6_find_hdr(const struct sk_buff * skb,unsigned int * offset,int target,unsigned short * fragoff,int * flags)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