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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 | ||
49ecc2e9 | 23 | static siphash_aligned_key_t syncookie6_secret[2]; |
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 | ||
7577bc82 | 117 | int __cookie_v6_check(const struct ipv6hdr *iph, const struct tcphdr *th) |
81eb6a14 | 118 | { |
7577bc82 | 119 | __u32 cookie = ntohl(th->ack_seq) - 1; |
c6aefafb | 120 | __u32 seq = ntohl(th->seq) - 1; |
7577bc82 KI |
121 | __u32 mssind; |
122 | ||
123 | mssind = check_tcp_syn_cookie(cookie, &iph->saddr, &iph->daddr, | |
124 | th->source, th->dest, seq); | |
c6aefafb | 125 | |
5918e2fb | 126 | return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0; |
c6aefafb | 127 | } |
81eb6a14 | 128 | EXPORT_SYMBOL_GPL(__cookie_v6_check); |
c6aefafb | 129 | |
8e7bab6b KI |
130 | static struct request_sock *cookie_tcp_check(struct net *net, struct sock *sk, |
131 | struct sk_buff *skb) | |
c6aefafb | 132 | { |
4957faad | 133 | struct tcp_options_received tcp_opt; |
84b114b9 | 134 | u32 tsoff = 0; |
8e7bab6b | 135 | int mss; |
c6aefafb | 136 | |
646697b9 FW |
137 | if (tcp_synq_no_recent_overflow(sk)) |
138 | goto out; | |
139 | ||
8e7bab6b KI |
140 | mss = __cookie_v6_check(ipv6_hdr(skb), tcp_hdr(skb)); |
141 | if (!mss) { | |
45c28509 | 142 | __NET_INC_STATS(net, LINUX_MIB_SYNCOOKIESFAILED); |
c6aefafb GG |
143 | goto out; |
144 | } | |
145 | ||
45c28509 | 146 | __NET_INC_STATS(net, LINUX_MIB_SYNCOOKIESRECV); |
c6aefafb | 147 | |
bb5b7c11 DM |
148 | /* check for timestamp cookie support */ |
149 | memset(&tcp_opt, 0, sizeof(tcp_opt)); | |
45c28509 | 150 | tcp_parse_options(net, skb, &tcp_opt, 0, NULL); |
bb5b7c11 | 151 | |
84b114b9 | 152 | if (tcp_opt.saw_tstamp && tcp_opt.rcv_tsecr) { |
45c28509 | 153 | tsoff = secure_tcpv6_ts_off(net, |
5d2ed052 | 154 | ipv6_hdr(skb)->daddr.s6_addr32, |
84b114b9 ED |
155 | ipv6_hdr(skb)->saddr.s6_addr32); |
156 | tcp_opt.rcv_tsecr -= tsoff; | |
157 | } | |
158 | ||
45c28509 | 159 | if (!cookie_timestamp_decode(net, &tcp_opt)) |
8c763681 | 160 | goto out; |
bb5b7c11 | 161 | |
8e7bab6b KI |
162 | return cookie_tcp_reqsk_alloc(&tcp6_request_sock_ops, sk, skb, |
163 | &tcp_opt, mss, tsoff); | |
164 | out: | |
165 | return ERR_PTR(-EINVAL); | |
166 | } | |
167 | ||
168 | struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb) | |
169 | { | |
170 | const struct tcphdr *th = tcp_hdr(skb); | |
171 | struct ipv6_pinfo *np = inet6_sk(sk); | |
172 | struct tcp_sock *tp = tcp_sk(sk); | |
173 | struct inet_request_sock *ireq; | |
174 | struct net *net = sock_net(sk); | |
175 | struct request_sock *req; | |
176 | struct dst_entry *dst; | |
177 | struct sock *ret = sk; | |
178 | __u8 rcv_wscale; | |
179 | int full_space; | |
ed43e76c | 180 | SKB_DR(reason); |
8e7bab6b KI |
181 | |
182 | if (!READ_ONCE(net->ipv4.sysctl_tcp_syncookies) || | |
183 | !th->ack || th->rst) | |
184 | goto out; | |
185 | ||
695751e3 KI |
186 | if (cookie_bpf_ok(skb)) { |
187 | req = cookie_bpf_check(sk, skb); | |
188 | } else { | |
189 | req = cookie_tcp_check(net, sk, skb); | |
190 | if (IS_ERR(req)) | |
191 | goto out; | |
192 | } | |
253541a3 JX |
193 | if (!req) { |
194 | SKB_DR_SET(reason, NO_SOCKET); | |
50468cdd | 195 | goto out_drop; |
253541a3 | 196 | } |
c6aefafb GG |
197 | |
198 | ireq = inet_rsk(req); | |
c6aefafb | 199 | |
634fb979 ED |
200 | ireq->ir_v6_rmt_addr = ipv6_hdr(skb)->saddr; |
201 | ireq->ir_v6_loc_addr = ipv6_hdr(skb)->daddr; | |
23be1e0e | 202 | |
253541a3 JX |
203 | if (security_inet_conn_request(sk, skb, req)) { |
204 | SKB_DR_SET(reason, SECURITY_HOOK); | |
23be1e0e | 205 | goto out_free; |
253541a3 | 206 | } |
23be1e0e | 207 | |
a224772d | 208 | if (ipv6_opt_accepted(sk, skb, &TCP_SKB_CB(skb)->header.h6) || |
c6aefafb GG |
209 | np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo || |
210 | np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) { | |
63354797 | 211 | refcount_inc(&skb->users); |
634fb979 | 212 | ireq->pktopts = skb; |
c6aefafb GG |
213 | } |
214 | ||
c6aefafb GG |
215 | /* So that link locals have meaning */ |
216 | if (!sk->sk_bound_dev_if && | |
634fb979 | 217 | ipv6_addr_type(&ireq->ir_v6_rmt_addr) & IPV6_ADDR_LINKLOCAL) |
870c3151 | 218 | ireq->ir_iif = tcp_v6_iif(skb); |
c6aefafb | 219 | |
7b0f570f | 220 | tcp_ao_syncookie(sk, skb, req, AF_INET6); |
06b22ef2 | 221 | |
c6aefafb GG |
222 | /* |
223 | * We need to lookup the dst_entry to get the correct window size. | |
224 | * This is taken from tcp_v6_syn_recv_sock. Somebody please enlighten | |
225 | * me if there is a preferred way. | |
226 | */ | |
227 | { | |
20c59de2 | 228 | struct in6_addr *final_p, final; |
4c9483b2 DM |
229 | struct flowi6 fl6; |
230 | memset(&fl6, 0, sizeof(fl6)); | |
231 | fl6.flowi6_proto = IPPROTO_TCP; | |
634fb979 | 232 | fl6.daddr = ireq->ir_v6_rmt_addr; |
45f6fad8 | 233 | final_p = fl6_update_dst(&fl6, rcu_dereference(np->opt), &final); |
634fb979 | 234 | fl6.saddr = ireq->ir_v6_loc_addr; |
6dd9a14e | 235 | fl6.flowi6_oif = ireq->ir_iif; |
84f39b08 | 236 | fl6.flowi6_mark = ireq->ir_mark; |
634fb979 | 237 | fl6.fl6_dport = ireq->ir_rmt_port; |
1958b856 | 238 | fl6.fl6_sport = inet_sk(sk)->inet_sport; |
e2d118a1 | 239 | fl6.flowi6_uid = sk->sk_uid; |
3df98d79 | 240 | security_req_classify_flow(req, flowi6_to_flowi_common(&fl6)); |
4c9483b2 | 241 | |
45c28509 | 242 | dst = ip6_dst_lookup_flow(net, sk, &fl6, final_p); |
253541a3 JX |
243 | if (IS_ERR(dst)) { |
244 | SKB_DR_SET(reason, IP_OUTNOROUTES); | |
1730554f | 245 | goto out_free; |
253541a3 | 246 | } |
c6aefafb GG |
247 | } |
248 | ||
f410cbea | 249 | req->rsk_window_clamp = READ_ONCE(tp->window_clamp) ? :dst_metric(dst, RTAX_WINDOW); |
909172a1 MW |
250 | /* limit the window selection if the user enforce a smaller rx buffer */ |
251 | full_space = tcp_full_space(sk); | |
252 | if (sk->sk_userlocks & SOCK_RCVBUF_LOCK && | |
253 | (req->rsk_window_clamp > full_space || req->rsk_window_clamp == 0)) | |
254 | req->rsk_window_clamp = full_space; | |
255 | ||
256 | tcp_select_initial_window(sk, full_space, req->mss, | |
ed53d0ab | 257 | &req->rsk_rcv_wnd, &req->rsk_window_clamp, |
31d12926 | 258 | ireq->wscale_ok, &rcv_wscale, |
259 | dst_metric(dst, RTAX_INITRWND)); | |
c6aefafb | 260 | |
956c0d61 KI |
261 | /* req->syncookie is set true only if ACK is validated |
262 | * by BPF kfunc, then, rcv_wscale is already configured. | |
263 | */ | |
695751e3 KI |
264 | if (!req->syncookie) |
265 | ireq->rcv_wscale = rcv_wscale; | |
8e7bab6b | 266 | ireq->ecn_ok &= cookie_ecn_ok(net, dst); |
c6aefafb | 267 | |
efce3d1f | 268 | ret = tcp_get_cookie_sock(sk, skb, req, dst); |
253541a3 JX |
269 | if (!ret) { |
270 | SKB_DR_SET(reason, NO_SOCKET); | |
ed43e76c | 271 | goto out_drop; |
253541a3 | 272 | } |
1730554f FW |
273 | out: |
274 | return ret; | |
275 | out_free: | |
276 | reqsk_free(req); | |
50468cdd | 277 | out_drop: |
ed43e76c | 278 | kfree_skb_reason(skb, reason); |
1730554f | 279 | return NULL; |
c6aefafb | 280 | } |