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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 | /* Table must be sorted. */ |
28 | static __u16 const msstab[] = { |
29 | 64, |
30 | 512, |
31 | 536, |
32 | 1280 - 60, |
33 | 1480 - 60, |
34 | 1500 - 60, |
35 | 4460 - 60, |
36 | 9000 - 60, |
37 | }; |
38 | |
39 | /* |
40 | * This (misnamed) value is the age of syncookie which is permitted. |
41 | * Its ideal value should be dependent on TCP_TIMEOUT_INIT and |
42 | * sysctl_tcp_retries1. It's a rather complicated formula (exponential |
43 | * backoff) to compute at runtime so it's currently hardcoded here. |
44 | */ |
45 | #define COUNTER_TRIES 4 |
46 | |
47 | static inline struct sock *get_cookie_sock(struct sock *sk, struct sk_buff *skb, |
48 | struct request_sock *req, |
49 | struct dst_entry *dst) |
50 | { |
51 | struct inet_connection_sock *icsk = inet_csk(sk); |
52 | struct sock *child; |
53 | |
54 | child = icsk->icsk_af_ops->syn_recv_sock(sk, skb, req, dst); |
55 | if (child) |
56 | inet_csk_reqsk_queue_add(sk, req, child); |
57 | else |
58 | reqsk_free(req); |
59 | |
60 | return child; |
61 | } |
62 | |
63 | static DEFINE_PER_CPU(__u32 [16 + 5 + SHA_WORKSPACE_WORDS], |
64 | ipv6_cookie_scratch); |
65 | |
66 | static u32 cookie_hash(const struct in6_addr *saddr, const struct in6_addr *daddr, |
67 | __be16 sport, __be16 dport, u32 count, int c) |
68 | { |
69 | __u32 *tmp = __get_cpu_var(ipv6_cookie_scratch); |
70 | |
71 | /* |
72 | * we have 320 bits of information to hash, copy in the remaining |
73 | * 192 bits required for sha_transform, from the syncookie_secret |
74 | * and overwrite the digest with the secret |
75 | */ |
76 | memcpy(tmp + 10, syncookie_secret[c], 44); |
77 | memcpy(tmp, saddr, 16); |
78 | memcpy(tmp + 4, daddr, 16); |
79 | tmp[8] = ((__force u32)sport << 16) + (__force u32)dport; |
80 | tmp[9] = count; |
81 | sha_transform(tmp + 16, (__u8 *)tmp, tmp + 16 + 5); |
82 | |
83 | return tmp[17]; |
84 | } |
85 | |
86 | static __u32 secure_tcp_syn_cookie(const struct in6_addr *saddr, |
87 | const struct in6_addr *daddr, |
88 | __be16 sport, __be16 dport, __u32 sseq, |
89 | __u32 count, __u32 data) |
90 | { |
91 | return (cookie_hash(saddr, daddr, sport, dport, 0, 0) + |
92 | sseq + (count << COOKIEBITS) + |
93 | ((cookie_hash(saddr, daddr, sport, dport, count, 1) + data) |
94 | & COOKIEMASK)); |
95 | } |
96 | |
97 | static __u32 check_tcp_syn_cookie(__u32 cookie, const struct in6_addr *saddr, |
98 | const struct in6_addr *daddr, __be16 sport, |
99 | __be16 dport, __u32 sseq, __u32 count, |
100 | __u32 maxdiff) |
101 | { |
102 | __u32 diff; |
103 | |
104 | cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq; |
105 | |
106 | diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS); |
107 | if (diff >= maxdiff) |
108 | return (__u32)-1; |
109 | |
110 | return (cookie - |
111 | cookie_hash(saddr, daddr, sport, dport, count - diff, 1)) |
112 | & COOKIEMASK; |
113 | } |
114 | |
115 | u32 __cookie_v6_init_sequence(const struct ipv6hdr *iph, |
116 | const struct tcphdr *th, __u16 *mssp) |
117 | { |
118 | int mssind; |
119 | const __u16 mss = *mssp; |
120 | |
121 | for (mssind = ARRAY_SIZE(msstab) - 1; mssind ; mssind--) |
122 | if (mss >= msstab[mssind]) |
123 | break; |
124 | |
125 | *mssp = msstab[mssind]; |
126 | |
127 | return secure_tcp_syn_cookie(&iph->saddr, &iph->daddr, th->source, |
128 | th->dest, ntohl(th->seq), |
129 | jiffies / (HZ * 60), mssind); |
130 | } |
131 | EXPORT_SYMBOL_GPL(__cookie_v6_init_sequence); |
132 | |
133 | __u32 cookie_v6_init_sequence(struct sock *sk, const struct sk_buff *skb, __u16 *mssp) |
134 | { |
135 | const struct ipv6hdr *iph = ipv6_hdr(skb); |
136 | const struct tcphdr *th = tcp_hdr(skb); |
137 | |
138 | tcp_synq_overflow(sk); |
139 | NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESSENT); |
140 | |
141 | return __cookie_v6_init_sequence(iph, th, mssp); |
142 | } |
143 | |
144 | int __cookie_v6_check(const struct ipv6hdr *iph, const struct tcphdr *th, |
145 | __u32 cookie) |
146 | { |
147 | __u32 seq = ntohl(th->seq) - 1; |
148 | __u32 mssind = check_tcp_syn_cookie(cookie, &iph->saddr, &iph->daddr, |
149 | th->source, th->dest, seq, |
150 | jiffies / (HZ * 60), COUNTER_TRIES); |
151 | |
152 | return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0; |
153 | } |
154 | EXPORT_SYMBOL_GPL(__cookie_v6_check); |
155 | |
156 | struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb) |
157 | { |
158 | struct tcp_options_received tcp_opt; |
159 | struct inet_request_sock *ireq; |
160 | struct inet6_request_sock *ireq6; |
161 | struct tcp_request_sock *treq; |
162 | struct ipv6_pinfo *np = inet6_sk(sk); |
163 | struct tcp_sock *tp = tcp_sk(sk); |
164 | const struct tcphdr *th = tcp_hdr(skb); |
165 | __u32 cookie = ntohl(th->ack_seq) - 1; |
166 | struct sock *ret = sk; |
167 | struct request_sock *req; |
168 | int mss; |
169 | struct dst_entry *dst; |
170 | __u8 rcv_wscale; |
171 | bool ecn_ok = false; |
172 | |
173 | if (!sysctl_tcp_syncookies || !th->ack || th->rst) |
174 | goto out; |
175 | |
176 | if (tcp_synq_no_recent_overflow(sk) || |
177 | (mss = __cookie_v6_check(ipv6_hdr(skb), th, cookie)) == 0) { |
178 | NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED); |
179 | goto out; |
180 | } |
181 | |
182 | NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV); |
183 | |
184 | /* check for timestamp cookie support */ |
185 | memset(&tcp_opt, 0, sizeof(tcp_opt)); |
186 | tcp_parse_options(skb, &tcp_opt, 0, NULL); |
187 | |
188 | if (!cookie_check_timestamp(&tcp_opt, sock_net(sk), &ecn_ok)) |
189 | goto out; |
190 | |
191 | ret = NULL; |
192 | req = inet6_reqsk_alloc(&tcp6_request_sock_ops); |
193 | if (!req) |
194 | goto out; |
195 | |
196 | ireq = inet_rsk(req); |
197 | ireq6 = inet6_rsk(req); |
198 | treq = tcp_rsk(req); |
199 | treq->listener = NULL; |
200 | |
201 | if (security_inet_conn_request(sk, skb, req)) |
202 | goto out_free; |
203 | |
204 | req->mss = mss; |
205 | ireq->rmt_port = th->source; |
206 | ireq->loc_port = th->dest; |
207 | ireq6->rmt_addr = ipv6_hdr(skb)->saddr; |
208 | ireq6->loc_addr = ipv6_hdr(skb)->daddr; |
209 | if (ipv6_opt_accepted(sk, skb) || |
210 | np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo || |
211 | np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) { |
212 | atomic_inc(&skb->users); |
213 | ireq6->pktopts = skb; |
214 | } |
215 | |
216 | ireq6->iif = sk->sk_bound_dev_if; |
217 | /* So that link locals have meaning */ |
218 | if (!sk->sk_bound_dev_if && |
219 | ipv6_addr_type(&ireq6->rmt_addr) & IPV6_ADDR_LINKLOCAL) |
220 | ireq6->iif = inet6_iif(skb); |
221 | |
222 | req->expires = 0UL; |
223 | req->num_retrans = 0; |
224 | ireq->ecn_ok = ecn_ok; |
225 | ireq->snd_wscale = tcp_opt.snd_wscale; |
226 | ireq->sack_ok = tcp_opt.sack_ok; |
227 | ireq->wscale_ok = tcp_opt.wscale_ok; |
228 | ireq->tstamp_ok = tcp_opt.saw_tstamp; |
229 | req->ts_recent = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0; |
230 | treq->snt_synack = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsecr : 0; |
231 | treq->rcv_isn = ntohl(th->seq) - 1; |
232 | treq->snt_isn = cookie; |
233 | |
234 | /* |
235 | * We need to lookup the dst_entry to get the correct window size. |
236 | * This is taken from tcp_v6_syn_recv_sock. Somebody please enlighten |
237 | * me if there is a preferred way. |
238 | */ |
239 | { |
240 | struct in6_addr *final_p, final; |
241 | struct flowi6 fl6; |
242 | memset(&fl6, 0, sizeof(fl6)); |
243 | fl6.flowi6_proto = IPPROTO_TCP; |
244 | fl6.daddr = ireq6->rmt_addr; |
245 | final_p = fl6_update_dst(&fl6, np->opt, &final); |
246 | fl6.saddr = ireq6->loc_addr; |
247 | fl6.flowi6_oif = sk->sk_bound_dev_if; |
248 | fl6.flowi6_mark = sk->sk_mark; |
249 | fl6.fl6_dport = inet_rsk(req)->rmt_port; |
250 | fl6.fl6_sport = inet_sk(sk)->inet_sport; |
251 | security_req_classify_flow(req, flowi6_to_flowi(&fl6)); |
252 | |
253 | dst = ip6_dst_lookup_flow(sk, &fl6, final_p, false); |
254 | if (IS_ERR(dst)) |
255 | goto out_free; |
256 | } |
257 | |
258 | req->window_clamp = tp->window_clamp ? :dst_metric(dst, RTAX_WINDOW); |
259 | tcp_select_initial_window(tcp_full_space(sk), req->mss, |
260 | &req->rcv_wnd, &req->window_clamp, |
261 | ireq->wscale_ok, &rcv_wscale, |
262 | dst_metric(dst, RTAX_INITRWND)); |
263 | |
264 | ireq->rcv_wscale = rcv_wscale; |
265 | |
266 | ret = get_cookie_sock(sk, skb, req, dst); |
267 | out: |
268 | return ret; |
269 | out_free: |
270 | reqsk_free(req); |
271 | return NULL; |
272 | } |
273 | |
274 |
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