1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
|
// SPDX-License-Identifier: GPL-2.0-or-later
/*
* IPv6 Syncookies implementation for the Linux kernel
*
* Authors:
* Glenn Griffin <ggriffin.kernel@gmail.com>
*
* Based on IPv4 implementation by Andi Kleen
* linux/net/ipv4/syncookies.c
*/
#include <linux/tcp.h>
#include <linux/random.h>
#include <linux/siphash.h>
#include <linux/kernel.h>
#include <net/secure_seq.h>
#include <net/ipv6.h>
#include <net/tcp.h>
#define COOKIEBITS 24 /* Upper bits store count */
#define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1)
static siphash_key_t syncookie6_secret[2] __read_mostly;
/* RFC 2460, Section 8.3:
* [ipv6 tcp] MSS must be computed as the maximum packet size minus 60 [..]
*
* Due to IPV6_MIN_MTU=1280 the lowest possible MSS is 1220, which allows
* using higher values than ipv4 tcp syncookies.
* The other values are chosen based on ethernet (1500 and 9k MTU), plus
* one that accounts for common encap (PPPoe) overhead. Table must be sorted.
*/
static __u16 const msstab[] = {
1280 - 60, /* IPV6_MIN_MTU - 60 */
1480 - 60,
1500 - 60,
9000 - 60,
};
static u32 cookie_hash(const struct in6_addr *saddr,
const struct in6_addr *daddr,
__be16 sport, __be16 dport, u32 count, int c)
{
const struct {
struct in6_addr saddr;
struct in6_addr daddr;
u32 count;
__be16 sport;
__be16 dport;
} __aligned(SIPHASH_ALIGNMENT) combined = {
.saddr = *saddr,
.daddr = *daddr,
.count = count,
.sport = sport,
.dport = dport
};
net_get_random_once(syncookie6_secret, sizeof(syncookie6_secret));
return siphash(&combined, offsetofend(typeof(combined), dport),
&syncookie6_secret[c]);
}
static __u32 secure_tcp_syn_cookie(const struct in6_addr *saddr,
const struct in6_addr *daddr,
__be16 sport, __be16 dport, __u32 sseq,
__u32 data)
{
u32 count = tcp_cookie_time();
return (cookie_hash(saddr, daddr, sport, dport, 0, 0) +
sseq + (count << COOKIEBITS) +
((cookie_hash(saddr, daddr, sport, dport, count, 1) + data)
& COOKIEMASK));
}
static __u32 check_tcp_syn_cookie(__u32 cookie, const struct in6_addr *saddr,
const struct in6_addr *daddr, __be16 sport,
__be16 dport, __u32 sseq)
{
__u32 diff, count = tcp_cookie_time();
cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq;
diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS);
if (diff >= MAX_SYNCOOKIE_AGE)
return (__u32)-1;
return (cookie -
cookie_hash(saddr, daddr, sport, dport, count - diff, 1))
& COOKIEMASK;
}
u32 __cookie_v6_init_sequence(const struct ipv6hdr *iph,
const struct tcphdr *th, __u16 *mssp)
{
int mssind;
const __u16 mss = *mssp;
for (mssind = ARRAY_SIZE(msstab) - 1; mssind ; mssind--)
if (mss >= msstab[mssind])
break;
*mssp = msstab[mssind];
return secure_tcp_syn_cookie(&iph->saddr, &iph->daddr, th->source,
th->dest, ntohl(th->seq), mssind);
}
EXPORT_SYMBOL_GPL(__cookie_v6_init_sequence);
__u32 cookie_v6_init_sequence(const struct sk_buff *skb, __u16 *mssp)
{
const struct ipv6hdr *iph = ipv6_hdr(skb);
const struct tcphdr *th = tcp_hdr(skb);
return __cookie_v6_init_sequence(iph, th, mssp);
}
int __cookie_v6_check(const struct ipv6hdr *iph, const struct tcphdr *th,
__u32 cookie)
{
__u32 seq = ntohl(th->seq) - 1;
__u32 mssind = check_tcp_syn_cookie(cookie, &iph->saddr, &iph->daddr,
th->source, th->dest, seq);
return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0;
}
EXPORT_SYMBOL_GPL(__cookie_v6_check);
struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
{
struct tcp_options_received tcp_opt;
struct inet_request_sock *ireq;
struct tcp_request_sock *treq;
struct ipv6_pinfo *np = inet6_sk(sk);
struct tcp_sock *tp = tcp_sk(sk);
const struct tcphdr *th = tcp_hdr(skb);
__u32 cookie = ntohl(th->ack_seq) - 1;
struct sock *ret = sk;
struct request_sock *req;
int mss;
struct dst_entry *dst;
__u8 rcv_wscale;
u32 tsoff = 0;
if (!sock_net(sk)->ipv4.sysctl_tcp_syncookies || !th->ack || th->rst)
goto out;
if (tcp_synq_no_recent_overflow(sk))
goto out;
mss = __cookie_v6_check(ipv6_hdr(skb), th, cookie);
if (mss == 0) {
__NET_INC_STATS(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED);
goto out;
}
__NET_INC_STATS(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV);
/* check for timestamp cookie support */
memset(&tcp_opt, 0, sizeof(tcp_opt));
tcp_parse_options(sock_net(sk), skb, &tcp_opt, 0, NULL);
if (tcp_opt.saw_tstamp && tcp_opt.rcv_tsecr) {
tsoff = secure_tcpv6_ts_off(sock_net(sk),
ipv6_hdr(skb)->daddr.s6_addr32,
ipv6_hdr(skb)->saddr.s6_addr32);
tcp_opt.rcv_tsecr -= tsoff;
}
if (!cookie_timestamp_decode(sock_net(sk), &tcp_opt))
goto out;
ret = NULL;
req = cookie_tcp_reqsk_alloc(&tcp6_request_sock_ops, sk, skb);
if (!req)
goto out;
ireq = inet_rsk(req);
treq = tcp_rsk(req);
treq->tfo_listener = false;
if (security_inet_conn_request(sk, skb, req))
goto out_free;
req->mss = mss;
ireq->ir_rmt_port = th->source;
ireq->ir_num = ntohs(th->dest);
ireq->ir_v6_rmt_addr = ipv6_hdr(skb)->saddr;
ireq->ir_v6_loc_addr = ipv6_hdr(skb)->daddr;
if (ipv6_opt_accepted(sk, skb, &TCP_SKB_CB(skb)->header.h6) ||
np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo ||
np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) {
refcount_inc(&skb->users);
ireq->pktopts = skb;
}
ireq->ir_iif = inet_request_bound_dev_if(sk, skb);
/* So that link locals have meaning */
if (!sk->sk_bound_dev_if &&
ipv6_addr_type(&ireq->ir_v6_rmt_addr) & IPV6_ADDR_LINKLOCAL)
ireq->ir_iif = tcp_v6_iif(skb);
ireq->ir_mark = inet_request_mark(sk, skb);
req->num_retrans = 0;
ireq->snd_wscale = tcp_opt.snd_wscale;
ireq->sack_ok = tcp_opt.sack_ok;
ireq->wscale_ok = tcp_opt.wscale_ok;
ireq->tstamp_ok = tcp_opt.saw_tstamp;
req->ts_recent = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0;
treq->snt_synack = 0;
treq->rcv_isn = ntohl(th->seq) - 1;
treq->snt_isn = cookie;
treq->ts_off = 0;
treq->txhash = net_tx_rndhash();
if (IS_ENABLED(CONFIG_SMC))
ireq->smc_ok = 0;
/*
* We need to lookup the dst_entry to get the correct window size.
* This is taken from tcp_v6_syn_recv_sock. Somebody please enlighten
* me if there is a preferred way.
*/
{
struct in6_addr *final_p, final;
struct flowi6 fl6;
memset(&fl6, 0, sizeof(fl6));
fl6.flowi6_proto = IPPROTO_TCP;
fl6.daddr = ireq->ir_v6_rmt_addr;
final_p = fl6_update_dst(&fl6, rcu_dereference(np->opt), &final);
fl6.saddr = ireq->ir_v6_loc_addr;
fl6.flowi6_oif = ireq->ir_iif;
fl6.flowi6_mark = ireq->ir_mark;
fl6.fl6_dport = ireq->ir_rmt_port;
fl6.fl6_sport = inet_sk(sk)->inet_sport;
fl6.flowi6_uid = sk->sk_uid;
security_req_classify_flow(req, flowi6_to_flowi_common(&fl6));
dst = ip6_dst_lookup_flow(sock_net(sk), sk, &fl6, final_p);
if (IS_ERR(dst))
goto out_free;
}
req->rsk_window_clamp = tp->window_clamp ? :dst_metric(dst, RTAX_WINDOW);
tcp_select_initial_window(sk, tcp_full_space(sk), req->mss,
&req->rsk_rcv_wnd, &req->rsk_window_clamp,
ireq->wscale_ok, &rcv_wscale,
dst_metric(dst, RTAX_INITRWND));
ireq->rcv_wscale = rcv_wscale;
ireq->ecn_ok = cookie_ecn_ok(&tcp_opt, sock_net(sk), dst);
ret = tcp_get_cookie_sock(sk, skb, req, dst, tsoff);
out:
return ret;
out_free:
reqsk_free(req);
return NULL;
}
|
