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2874c5fd | 1 | // SPDX-License-Identifier: GPL-2.0-or-later |
c6aefafb GG |
2 | /* |
3 | * IPv6 Syncookies implementation for the Linux kernel | |
4 | * | |
5 | * Authors: | |
6 | * Glenn Griffin <ggriffin.kernel@gmail.com> | |
7 | * | |
8 | * Based on IPv4 implementation by Andi Kleen | |
9 | * linux/net/ipv4/syncookies.c | |
c6aefafb GG |
10 | */ |
11 | ||
12 | #include <linux/tcp.h> | |
13 | #include <linux/random.h> | |
fe62d05b | 14 | #include <linux/siphash.h> |
c6aefafb | 15 | #include <linux/kernel.h> |
84b114b9 | 16 | #include <net/secure_seq.h> |
c6aefafb GG |
17 | #include <net/ipv6.h> |
18 | #include <net/tcp.h> | |
19 | ||
c6aefafb GG |
20 | #define COOKIEBITS 24 /* Upper bits store count */ |
21 | #define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1) | |
22 | ||
fe62d05b | 23 | static siphash_key_t syncookie6_secret[2] __read_mostly; |
b23a002f | 24 | |
08629354 FW |
25 | /* RFC 2460, Section 8.3: |
26 | * [ipv6 tcp] MSS must be computed as the maximum packet size minus 60 [..] | |
27 | * | |
28 | * Due to IPV6_MIN_MTU=1280 the lowest possible MSS is 1220, which allows | |
29 | * using higher values than ipv4 tcp syncookies. | |
30 | * The other values are chosen based on ethernet (1500 and 9k MTU), plus | |
31 | * one that accounts for common encap (PPPoe) overhead. Table must be sorted. | |
32 | */ | |
c6aefafb | 33 | static __u16 const msstab[] = { |
08629354 | 34 | 1280 - 60, /* IPV6_MIN_MTU - 60 */ |
5918e2fb FW |
35 | 1480 - 60, |
36 | 1500 - 60, | |
5918e2fb | 37 | 9000 - 60, |
c6aefafb | 38 | }; |
c6aefafb | 39 | |
fe62d05b JD |
40 | static u32 cookie_hash(const struct in6_addr *saddr, |
41 | const struct in6_addr *daddr, | |
c6aefafb GG |
42 | __be16 sport, __be16 dport, u32 count, int c) |
43 | { | |
fe62d05b JD |
44 | const struct { |
45 | struct in6_addr saddr; | |
46 | struct in6_addr daddr; | |
47 | u32 count; | |
48 | __be16 sport; | |
49 | __be16 dport; | |
50 | } __aligned(SIPHASH_ALIGNMENT) combined = { | |
51 | .saddr = *saddr, | |
52 | .daddr = *daddr, | |
53 | .count = count, | |
54 | .sport = sport, | |
55 | .dport = dport | |
56 | }; | |
b23a002f HFS |
57 | |
58 | net_get_random_once(syncookie6_secret, sizeof(syncookie6_secret)); | |
fe62d05b JD |
59 | return siphash(&combined, offsetofend(typeof(combined), dport), |
60 | &syncookie6_secret[c]); | |
c6aefafb GG |
61 | } |
62 | ||
b71d1d42 ED |
63 | static __u32 secure_tcp_syn_cookie(const struct in6_addr *saddr, |
64 | const struct in6_addr *daddr, | |
c6aefafb | 65 | __be16 sport, __be16 dport, __u32 sseq, |
8c27bd75 | 66 | __u32 data) |
c6aefafb | 67 | { |
8c27bd75 | 68 | u32 count = tcp_cookie_time(); |
c6aefafb GG |
69 | return (cookie_hash(saddr, daddr, sport, dport, 0, 0) + |
70 | sseq + (count << COOKIEBITS) + | |
71 | ((cookie_hash(saddr, daddr, sport, dport, count, 1) + data) | |
72 | & COOKIEMASK)); | |
73 | } | |
74 | ||
b71d1d42 ED |
75 | static __u32 check_tcp_syn_cookie(__u32 cookie, const struct in6_addr *saddr, |
76 | const struct in6_addr *daddr, __be16 sport, | |
8c27bd75 | 77 | __be16 dport, __u32 sseq) |
c6aefafb | 78 | { |
8c27bd75 | 79 | __u32 diff, count = tcp_cookie_time(); |
c6aefafb GG |
80 | |
81 | cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq; | |
82 | ||
83 | diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS); | |
8c27bd75 | 84 | if (diff >= MAX_SYNCOOKIE_AGE) |
c6aefafb GG |
85 | return (__u32)-1; |
86 | ||
87 | return (cookie - | |
88 | cookie_hash(saddr, daddr, sport, dport, count - diff, 1)) | |
89 | & COOKIEMASK; | |
90 | } | |
91 | ||
81eb6a14 PM |
92 | u32 __cookie_v6_init_sequence(const struct ipv6hdr *iph, |
93 | const struct tcphdr *th, __u16 *mssp) | |
c6aefafb | 94 | { |
c6aefafb GG |
95 | int mssind; |
96 | const __u16 mss = *mssp; | |
97 | ||
5918e2fb FW |
98 | for (mssind = ARRAY_SIZE(msstab) - 1; mssind ; mssind--) |
99 | if (mss >= msstab[mssind]) | |
100 | break; | |
101 | ||
102 | *mssp = msstab[mssind]; | |
c6aefafb | 103 | |
c6aefafb | 104 | return secure_tcp_syn_cookie(&iph->saddr, &iph->daddr, th->source, |
8c27bd75 | 105 | th->dest, ntohl(th->seq), mssind); |
c6aefafb | 106 | } |
81eb6a14 | 107 | EXPORT_SYMBOL_GPL(__cookie_v6_init_sequence); |
c6aefafb | 108 | |
3f684b4b | 109 | __u32 cookie_v6_init_sequence(const struct sk_buff *skb, __u16 *mssp) |
c6aefafb | 110 | { |
b71d1d42 | 111 | const struct ipv6hdr *iph = ipv6_hdr(skb); |
c6aefafb | 112 | const struct tcphdr *th = tcp_hdr(skb); |
81eb6a14 | 113 | |
81eb6a14 PM |
114 | return __cookie_v6_init_sequence(iph, th, mssp); |
115 | } | |
116 | ||
117 | int __cookie_v6_check(const struct ipv6hdr *iph, const struct tcphdr *th, | |
118 | __u32 cookie) | |
119 | { | |
c6aefafb GG |
120 | __u32 seq = ntohl(th->seq) - 1; |
121 | __u32 mssind = check_tcp_syn_cookie(cookie, &iph->saddr, &iph->daddr, | |
8c27bd75 | 122 | th->source, th->dest, seq); |
c6aefafb | 123 | |
5918e2fb | 124 | return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0; |
c6aefafb | 125 | } |
81eb6a14 | 126 | EXPORT_SYMBOL_GPL(__cookie_v6_check); |
c6aefafb GG |
127 | |
128 | struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb) | |
129 | { | |
4957faad | 130 | struct tcp_options_received tcp_opt; |
c6aefafb | 131 | struct inet_request_sock *ireq; |
c6aefafb GG |
132 | struct tcp_request_sock *treq; |
133 | struct ipv6_pinfo *np = inet6_sk(sk); | |
134 | struct tcp_sock *tp = tcp_sk(sk); | |
135 | const struct tcphdr *th = tcp_hdr(skb); | |
136 | __u32 cookie = ntohl(th->ack_seq) - 1; | |
137 | struct sock *ret = sk; | |
138 | struct request_sock *req; | |
139 | int mss; | |
140 | struct dst_entry *dst; | |
141 | __u8 rcv_wscale; | |
84b114b9 | 142 | u32 tsoff = 0; |
c6aefafb | 143 | |
12ed8244 | 144 | if (!sock_net(sk)->ipv4.sysctl_tcp_syncookies || !th->ack || th->rst) |
c6aefafb GG |
145 | goto out; |
146 | ||
646697b9 FW |
147 | if (tcp_synq_no_recent_overflow(sk)) |
148 | goto out; | |
149 | ||
150 | mss = __cookie_v6_check(ipv6_hdr(skb), th, cookie); | |
151 | if (mss == 0) { | |
02a1d6e7 | 152 | __NET_INC_STATS(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED); |
c6aefafb GG |
153 | goto out; |
154 | } | |
155 | ||
02a1d6e7 | 156 | __NET_INC_STATS(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV); |
c6aefafb | 157 | |
bb5b7c11 DM |
158 | /* check for timestamp cookie support */ |
159 | memset(&tcp_opt, 0, sizeof(tcp_opt)); | |
eed29f17 | 160 | tcp_parse_options(sock_net(sk), skb, &tcp_opt, 0, NULL); |
bb5b7c11 | 161 | |
84b114b9 | 162 | if (tcp_opt.saw_tstamp && tcp_opt.rcv_tsecr) { |
5d2ed052 ED |
163 | tsoff = secure_tcpv6_ts_off(sock_net(sk), |
164 | ipv6_hdr(skb)->daddr.s6_addr32, | |
84b114b9 ED |
165 | ipv6_hdr(skb)->saddr.s6_addr32); |
166 | tcp_opt.rcv_tsecr -= tsoff; | |
167 | } | |
168 | ||
f9301034 | 169 | if (!cookie_timestamp_decode(sock_net(sk), &tcp_opt)) |
8c763681 | 170 | goto out; |
bb5b7c11 | 171 | |
c6aefafb | 172 | ret = NULL; |
a1a5344d | 173 | req = inet_reqsk_alloc(&tcp6_request_sock_ops, sk, false); |
c6aefafb GG |
174 | if (!req) |
175 | goto out; | |
176 | ||
177 | ireq = inet_rsk(req); | |
c6aefafb | 178 | treq = tcp_rsk(req); |
9439ce00 | 179 | treq->tfo_listener = false; |
c6aefafb | 180 | |
ae2dd716 FW |
181 | if (IS_ENABLED(CONFIG_MPTCP)) |
182 | treq->is_mptcp = 0; | |
183 | ||
1730554f FW |
184 | if (security_inet_conn_request(sk, skb, req)) |
185 | goto out_free; | |
c6aefafb GG |
186 | |
187 | req->mss = mss; | |
634fb979 | 188 | ireq->ir_rmt_port = th->source; |
b44084c2 | 189 | ireq->ir_num = ntohs(th->dest); |
634fb979 ED |
190 | ireq->ir_v6_rmt_addr = ipv6_hdr(skb)->saddr; |
191 | ireq->ir_v6_loc_addr = ipv6_hdr(skb)->daddr; | |
a224772d | 192 | if (ipv6_opt_accepted(sk, skb, &TCP_SKB_CB(skb)->header.h6) || |
c6aefafb GG |
193 | np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo || |
194 | np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) { | |
63354797 | 195 | refcount_inc(&skb->users); |
634fb979 | 196 | ireq->pktopts = skb; |
c6aefafb GG |
197 | } |
198 | ||
6dd9a14e | 199 | ireq->ir_iif = inet_request_bound_dev_if(sk, skb); |
c6aefafb GG |
200 | /* So that link locals have meaning */ |
201 | if (!sk->sk_bound_dev_if && | |
634fb979 | 202 | ipv6_addr_type(&ireq->ir_v6_rmt_addr) & IPV6_ADDR_LINKLOCAL) |
870c3151 | 203 | ireq->ir_iif = tcp_v6_iif(skb); |
c6aefafb | 204 | |
84f39b08 LC |
205 | ireq->ir_mark = inet_request_mark(sk, skb); |
206 | ||
e6c022a4 | 207 | req->num_retrans = 0; |
bb5b7c11 | 208 | ireq->snd_wscale = tcp_opt.snd_wscale; |
bb5b7c11 DM |
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; | |
9a568de4 | 213 | treq->snt_synack = 0; |
c6aefafb GG |
214 | treq->rcv_isn = ntohl(th->seq) - 1; |
215 | treq->snt_isn = cookie; | |
95a22cae | 216 | treq->ts_off = 0; |
18bcf290 | 217 | treq->txhash = net_tx_rndhash(); |
bc58a1ba HW |
218 | if (IS_ENABLED(CONFIG_SMC)) |
219 | ireq->smc_ok = 0; | |
c6aefafb GG |
220 | |
221 | /* | |
222 | * We need to lookup the dst_entry to get the correct window size. | |
223 | * This is taken from tcp_v6_syn_recv_sock. Somebody please enlighten | |
224 | * me if there is a preferred way. | |
225 | */ | |
226 | { | |
20c59de2 | 227 | struct in6_addr *final_p, final; |
4c9483b2 DM |
228 | struct flowi6 fl6; |
229 | memset(&fl6, 0, sizeof(fl6)); | |
230 | fl6.flowi6_proto = IPPROTO_TCP; | |
634fb979 | 231 | fl6.daddr = ireq->ir_v6_rmt_addr; |
45f6fad8 | 232 | final_p = fl6_update_dst(&fl6, rcu_dereference(np->opt), &final); |
634fb979 | 233 | fl6.saddr = ireq->ir_v6_loc_addr; |
6dd9a14e | 234 | fl6.flowi6_oif = ireq->ir_iif; |
84f39b08 | 235 | fl6.flowi6_mark = ireq->ir_mark; |
634fb979 | 236 | fl6.fl6_dport = ireq->ir_rmt_port; |
1958b856 | 237 | fl6.fl6_sport = inet_sk(sk)->inet_sport; |
e2d118a1 | 238 | fl6.flowi6_uid = sk->sk_uid; |
4c9483b2 DM |
239 | security_req_classify_flow(req, flowi6_to_flowi(&fl6)); |
240 | ||
c4e85f73 | 241 | dst = ip6_dst_lookup_flow(sock_net(sk), sk, &fl6, final_p); |
68d0c6d3 | 242 | if (IS_ERR(dst)) |
1730554f | 243 | goto out_free; |
c6aefafb GG |
244 | } |
245 | ||
ed53d0ab | 246 | req->rsk_window_clamp = tp->window_clamp ? :dst_metric(dst, RTAX_WINDOW); |
ceef9ab6 | 247 | tcp_select_initial_window(sk, tcp_full_space(sk), req->mss, |
ed53d0ab | 248 | &req->rsk_rcv_wnd, &req->rsk_window_clamp, |
31d12926 | 249 | ireq->wscale_ok, &rcv_wscale, |
250 | dst_metric(dst, RTAX_INITRWND)); | |
c6aefafb GG |
251 | |
252 | ireq->rcv_wscale = rcv_wscale; | |
f7b3bec6 | 253 | ireq->ecn_ok = cookie_ecn_ok(&tcp_opt, sock_net(sk), dst); |
c6aefafb | 254 | |
84b114b9 | 255 | ret = tcp_get_cookie_sock(sk, skb, req, dst, tsoff); |
1730554f FW |
256 | out: |
257 | return ret; | |
258 | out_free: | |
259 | reqsk_free(req); | |
260 | return NULL; | |
c6aefafb | 261 | } |