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1 | /* | |
2 | * IPv6 Syncookies implementation for the Linux kernel | |
3 | * | |
4 | * Authors: | |
5 | * Glenn Griffin <ggriffin.kernel@gmail.com> | |
6 | * | |
7 | * Based on IPv4 implementation by Andi Kleen | |
8 | * linux/net/ipv4/syncookies.c | |
9 | * | |
10 | * This program is free software; you can redistribute it and/or | |
11 | * modify it under the terms of the GNU General Public License | |
12 | * as published by the Free Software Foundation; either version | |
13 | * 2 of the License, or (at your option) any later version. | |
14 | * | |
15 | */ | |
16 | ||
17 | #include <linux/tcp.h> | |
18 | #include <linux/random.h> | |
19 | #include <linux/cryptohash.h> | |
20 | #include <linux/kernel.h> | |
21 | #include <net/ipv6.h> | |
22 | #include <net/tcp.h> | |
23 | ||
24 | #define COOKIEBITS 24 /* Upper bits store count */ | |
25 | #define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1) | |
26 | ||
27 | static u32 syncookie6_secret[2][16-4+SHA_DIGEST_WORDS] __read_mostly; | |
28 | ||
29 | /* RFC 2460, Section 8.3: | |
30 | * [ipv6 tcp] MSS must be computed as the maximum packet size minus 60 [..] | |
31 | * | |
32 | * Due to IPV6_MIN_MTU=1280 the lowest possible MSS is 1220, which allows | |
33 | * using higher values than ipv4 tcp syncookies. | |
34 | * The other values are chosen based on ethernet (1500 and 9k MTU), plus | |
35 | * one that accounts for common encap (PPPoe) overhead. Table must be sorted. | |
36 | */ | |
37 | static __u16 const msstab[] = { | |
38 | 1280 - 60, /* IPV6_MIN_MTU - 60 */ | |
39 | 1480 - 60, | |
40 | 1500 - 60, | |
41 | 9000 - 60, | |
42 | }; | |
43 | ||
44 | static DEFINE_PER_CPU(__u32 [16 + 5 + SHA_WORKSPACE_WORDS], | |
45 | ipv6_cookie_scratch); | |
46 | ||
47 | static u32 cookie_hash(const struct in6_addr *saddr, const struct in6_addr *daddr, | |
48 | __be16 sport, __be16 dport, u32 count, int c) | |
49 | { | |
50 | __u32 *tmp; | |
51 | ||
52 | net_get_random_once(syncookie6_secret, sizeof(syncookie6_secret)); | |
53 | ||
54 | tmp = this_cpu_ptr(ipv6_cookie_scratch); | |
55 | ||
56 | /* | |
57 | * we have 320 bits of information to hash, copy in the remaining | |
58 | * 192 bits required for sha_transform, from the syncookie6_secret | |
59 | * and overwrite the digest with the secret | |
60 | */ | |
61 | memcpy(tmp + 10, syncookie6_secret[c], 44); | |
62 | memcpy(tmp, saddr, 16); | |
63 | memcpy(tmp + 4, daddr, 16); | |
64 | tmp[8] = ((__force u32)sport << 16) + (__force u32)dport; | |
65 | tmp[9] = count; | |
66 | sha_transform(tmp + 16, (__u8 *)tmp, tmp + 16 + 5); | |
67 | ||
68 | return tmp[17]; | |
69 | } | |
70 | ||
71 | static __u32 secure_tcp_syn_cookie(const struct in6_addr *saddr, | |
72 | const struct in6_addr *daddr, | |
73 | __be16 sport, __be16 dport, __u32 sseq, | |
74 | __u32 data) | |
75 | { | |
76 | u32 count = tcp_cookie_time(); | |
77 | return (cookie_hash(saddr, daddr, sport, dport, 0, 0) + | |
78 | sseq + (count << COOKIEBITS) + | |
79 | ((cookie_hash(saddr, daddr, sport, dport, count, 1) + data) | |
80 | & COOKIEMASK)); | |
81 | } | |
82 | ||
83 | static __u32 check_tcp_syn_cookie(__u32 cookie, const struct in6_addr *saddr, | |
84 | const struct in6_addr *daddr, __be16 sport, | |
85 | __be16 dport, __u32 sseq) | |
86 | { | |
87 | __u32 diff, count = tcp_cookie_time(); | |
88 | ||
89 | cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq; | |
90 | ||
91 | diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS); | |
92 | if (diff >= MAX_SYNCOOKIE_AGE) | |
93 | return (__u32)-1; | |
94 | ||
95 | return (cookie - | |
96 | cookie_hash(saddr, daddr, sport, dport, count - diff, 1)) | |
97 | & COOKIEMASK; | |
98 | } | |
99 | ||
100 | u32 __cookie_v6_init_sequence(const struct ipv6hdr *iph, | |
101 | const struct tcphdr *th, __u16 *mssp) | |
102 | { | |
103 | int mssind; | |
104 | const __u16 mss = *mssp; | |
105 | ||
106 | for (mssind = ARRAY_SIZE(msstab) - 1; mssind ; mssind--) | |
107 | if (mss >= msstab[mssind]) | |
108 | break; | |
109 | ||
110 | *mssp = msstab[mssind]; | |
111 | ||
112 | return secure_tcp_syn_cookie(&iph->saddr, &iph->daddr, th->source, | |
113 | th->dest, ntohl(th->seq), mssind); | |
114 | } | |
115 | EXPORT_SYMBOL_GPL(__cookie_v6_init_sequence); | |
116 | ||
117 | __u32 cookie_v6_init_sequence(struct sock *sk, const struct sk_buff *skb, __u16 *mssp) | |
118 | { | |
119 | const struct ipv6hdr *iph = ipv6_hdr(skb); | |
120 | const struct tcphdr *th = tcp_hdr(skb); | |
121 | ||
122 | tcp_synq_overflow(sk); | |
123 | NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESSENT); | |
124 | ||
125 | return __cookie_v6_init_sequence(iph, th, mssp); | |
126 | } | |
127 | ||
128 | int __cookie_v6_check(const struct ipv6hdr *iph, const struct tcphdr *th, | |
129 | __u32 cookie) | |
130 | { | |
131 | __u32 seq = ntohl(th->seq) - 1; | |
132 | __u32 mssind = check_tcp_syn_cookie(cookie, &iph->saddr, &iph->daddr, | |
133 | th->source, th->dest, seq); | |
134 | ||
135 | return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0; | |
136 | } | |
137 | EXPORT_SYMBOL_GPL(__cookie_v6_check); | |
138 | ||
139 | struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb) | |
140 | { | |
141 | struct tcp_options_received tcp_opt; | |
142 | struct inet_request_sock *ireq; | |
143 | struct tcp_request_sock *treq; | |
144 | struct ipv6_pinfo *np = inet6_sk(sk); | |
145 | struct tcp_sock *tp = tcp_sk(sk); | |
146 | const struct tcphdr *th = tcp_hdr(skb); | |
147 | __u32 cookie = ntohl(th->ack_seq) - 1; | |
148 | struct sock *ret = sk; | |
149 | struct request_sock *req; | |
150 | int mss; | |
151 | struct dst_entry *dst; | |
152 | __u8 rcv_wscale; | |
153 | ||
154 | if (!sysctl_tcp_syncookies || !th->ack || th->rst) | |
155 | goto out; | |
156 | ||
157 | if (tcp_synq_no_recent_overflow(sk)) | |
158 | goto out; | |
159 | ||
160 | mss = __cookie_v6_check(ipv6_hdr(skb), th, cookie); | |
161 | if (mss == 0) { | |
162 | NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED); | |
163 | goto out; | |
164 | } | |
165 | ||
166 | NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV); | |
167 | ||
168 | /* check for timestamp cookie support */ | |
169 | memset(&tcp_opt, 0, sizeof(tcp_opt)); | |
170 | tcp_parse_options(skb, &tcp_opt, 0, NULL); | |
171 | ||
172 | if (!cookie_timestamp_decode(&tcp_opt)) | |
173 | goto out; | |
174 | ||
175 | ret = NULL; | |
176 | req = inet_reqsk_alloc(&tcp6_request_sock_ops, sk); | |
177 | if (!req) | |
178 | goto out; | |
179 | ||
180 | ireq = inet_rsk(req); | |
181 | treq = tcp_rsk(req); | |
182 | treq->tfo_listener = false; | |
183 | ||
184 | if (security_inet_conn_request(sk, skb, req)) | |
185 | goto out_free; | |
186 | ||
187 | req->mss = mss; | |
188 | ireq->ir_rmt_port = th->source; | |
189 | ireq->ir_num = ntohs(th->dest); | |
190 | ireq->ir_v6_rmt_addr = ipv6_hdr(skb)->saddr; | |
191 | ireq->ir_v6_loc_addr = ipv6_hdr(skb)->daddr; | |
192 | if (ipv6_opt_accepted(sk, skb, &TCP_SKB_CB(skb)->header.h6) || | |
193 | np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo || | |
194 | np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) { | |
195 | atomic_inc(&skb->users); | |
196 | ireq->pktopts = skb; | |
197 | } | |
198 | ||
199 | ireq->ir_iif = sk->sk_bound_dev_if; | |
200 | /* So that link locals have meaning */ | |
201 | if (!sk->sk_bound_dev_if && | |
202 | ipv6_addr_type(&ireq->ir_v6_rmt_addr) & IPV6_ADDR_LINKLOCAL) | |
203 | ireq->ir_iif = tcp_v6_iif(skb); | |
204 | ||
205 | ireq->ir_mark = inet_request_mark(sk, skb); | |
206 | ||
207 | req->num_retrans = 0; | |
208 | ireq->snd_wscale = tcp_opt.snd_wscale; | |
209 | ireq->sack_ok = tcp_opt.sack_ok; | |
210 | ireq->wscale_ok = tcp_opt.wscale_ok; | |
211 | ireq->tstamp_ok = tcp_opt.saw_tstamp; | |
212 | req->ts_recent = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0; | |
213 | treq->snt_synack.v64 = 0; | |
214 | treq->rcv_isn = ntohl(th->seq) - 1; | |
215 | treq->snt_isn = cookie; | |
216 | ||
217 | /* | |
218 | * We need to lookup the dst_entry to get the correct window size. | |
219 | * This is taken from tcp_v6_syn_recv_sock. Somebody please enlighten | |
220 | * me if there is a preferred way. | |
221 | */ | |
222 | { | |
223 | struct in6_addr *final_p, final; | |
224 | struct flowi6 fl6; | |
225 | memset(&fl6, 0, sizeof(fl6)); | |
226 | fl6.flowi6_proto = IPPROTO_TCP; | |
227 | fl6.daddr = ireq->ir_v6_rmt_addr; | |
228 | final_p = fl6_update_dst(&fl6, np->opt, &final); | |
229 | fl6.saddr = ireq->ir_v6_loc_addr; | |
230 | fl6.flowi6_oif = sk->sk_bound_dev_if; | |
231 | fl6.flowi6_mark = ireq->ir_mark; | |
232 | fl6.fl6_dport = ireq->ir_rmt_port; | |
233 | fl6.fl6_sport = inet_sk(sk)->inet_sport; | |
234 | security_req_classify_flow(req, flowi6_to_flowi(&fl6)); | |
235 | ||
236 | dst = ip6_dst_lookup_flow(sk, &fl6, final_p); | |
237 | if (IS_ERR(dst)) | |
238 | goto out_free; | |
239 | } | |
240 | ||
241 | req->window_clamp = tp->window_clamp ? :dst_metric(dst, RTAX_WINDOW); | |
242 | tcp_select_initial_window(tcp_full_space(sk), req->mss, | |
243 | &req->rcv_wnd, &req->window_clamp, | |
244 | ireq->wscale_ok, &rcv_wscale, | |
245 | dst_metric(dst, RTAX_INITRWND)); | |
246 | ||
247 | ireq->rcv_wscale = rcv_wscale; | |
248 | ireq->ecn_ok = cookie_ecn_ok(&tcp_opt, sock_net(sk), dst); | |
249 | ||
250 | ret = tcp_get_cookie_sock(sk, skb, req, dst); | |
251 | out: | |
252 | return ret; | |
253 | out_free: | |
254 | reqsk_free(req); | |
255 | return NULL; | |
256 | } |