Release 4.11 net/ipv4/syncookies.c
/*
* Syncookies implementation for the Linux kernel
*
* Copyright (C) 1997 Andi Kleen
* Based on ideas by D.J.Bernstein and Eric Schenk.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version
* 2 of the License, or (at your option) any later version.
*/
#include <linux/tcp.h>
#include <linux/slab.h>
#include <linux/random.h>
#include <linux/siphash.h>
#include <linux/kernel.h>
#include <linux/export.h>
#include <net/tcp.h>
#include <net/route.h>
static siphash_key_t syncookie_secret[2] __read_mostly;
#define COOKIEBITS 24
/* Upper bits store count */
#define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1)
/* TCP Timestamp: 6 lowest bits of timestamp sent in the cookie SYN-ACK
* stores TCP options:
*
* MSB LSB
* | 31 ... 6 | 5 | 4 | 3 2 1 0 |
* | Timestamp | ECN | SACK | WScale |
*
* When we receive a valid cookie-ACK, we look at the echoed tsval (if
* any) to figure out which TCP options we should use for the rebuilt
* connection.
*
* A WScale setting of '0xf' (which is an invalid scaling value)
* means that original syn did not include the TCP window scaling option.
*/
#define TS_OPT_WSCALE_MASK 0xf
#define TS_OPT_SACK BIT(4)
#define TS_OPT_ECN BIT(5)
/* There is no TS_OPT_TIMESTAMP:
* if ACK contains timestamp option, we already know it was
* requested/supported by the syn/synack exchange.
*/
#define TSBITS 6
#define TSMASK (((__u32)1 << TSBITS) - 1)
static u32 cookie_hash(__be32 saddr, __be32 daddr, __be16 sport, __be16 dport,
u32 count, int c)
{
net_get_random_once(syncookie_secret, sizeof(syncookie_secret));
return siphash_4u32((__force u32)saddr, (__force u32)daddr,
(__force u32)sport << 16 | (__force u32)dport,
count, &syncookie_secret[c]);
}
Contributors
Person | Tokens | Prop | Commits | CommitProp |
Matt Mackall | 32 | 44.44% | 1 | 25.00% |
Al Viro | 20 | 27.78% | 1 | 25.00% |
Jason A. Donenfeld | 10 | 13.89% | 1 | 25.00% |
Hannes Frederic Sowa | 10 | 13.89% | 1 | 25.00% |
Total | 72 | 100.00% | 4 | 100.00% |
/*
* when syncookies are in effect and tcp timestamps are enabled we encode
* tcp options in the lower bits of the timestamp value that will be
* sent in the syn-ack.
* Since subsequent timestamps use the normal tcp_time_stamp value, we
* must make sure that the resulting initial timestamp is <= tcp_time_stamp.
*/
__u32 cookie_init_timestamp(struct request_sock *req)
{
struct inet_request_sock *ireq;
u32 ts, ts_now = tcp_time_stamp;
u32 options = 0;
ireq = inet_rsk(req);
options = ireq->wscale_ok ? ireq->snd_wscale : TS_OPT_WSCALE_MASK;
if (ireq->sack_ok)
options |= TS_OPT_SACK;
if (ireq->ecn_ok)
options |= TS_OPT_ECN;
ts = ts_now & ~TSMASK;
ts |= options;
if (ts > ts_now) {
ts >>= TSBITS;
ts--;
ts <<= TSBITS;
ts |= options;
}
return ts;
}
Contributors
Person | Tokens | Prop | Commits | CommitProp |
Florian Westphal | 103 | 100.00% | 4 | 100.00% |
Total | 103 | 100.00% | 4 | 100.00% |
static __u32 secure_tcp_syn_cookie(__be32 saddr, __be32 daddr, __be16 sport,
__be16 dport, __u32 sseq, __u32 data)
{
/*
* Compute the secure sequence number.
* The output should be:
* HASH(sec1,saddr,sport,daddr,dport,sec1) + sseq + (count * 2^24)
* + (HASH(sec2,saddr,sport,daddr,dport,count,sec2) % 2^24).
* Where sseq is their sequence number and count increases every
* minute by 1.
* As an extra hack, we add a small "data" value that encodes the
* MSS into the second hash value.
*/
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));
}
Contributors
Person | Tokens | Prop | Commits | CommitProp |
Matt Mackall | 69 | 86.25% | 1 | 25.00% |
Florian Westphal | 6 | 7.50% | 1 | 25.00% |
Al Viro | 4 | 5.00% | 1 | 25.00% |
Hideaki Yoshifuji / 吉藤英明 | 1 | 1.25% | 1 | 25.00% |
Total | 80 | 100.00% | 4 | 100.00% |
/*
* This retrieves the small "data" value from the syncookie.
* If the syncookie is bad, the data returned will be out of
* range. This must be checked by the caller.
*
* The count value used to generate the cookie must be less than
* MAX_SYNCOOKIE_AGE minutes in the past.
* The return value (__u32)-1 if this test fails.
*/
static __u32 check_tcp_syn_cookie(__u32 cookie, __be32 saddr, __be32 daddr,
__be16 sport, __be16 dport, __u32 sseq)
{
u32 diff, count = tcp_cookie_time();
/* Strip away the layers from the cookie */
cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq;
/* Cookie is now reduced to (count * 2^24) ^ (hash % 2^24) */
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; /* Leaving the data behind */
}
Contributors
Person | Tokens | Prop | Commits | CommitProp |
Matt Mackall | 102 | 90.27% | 1 | 33.33% |
Florian Westphal | 7 | 6.19% | 1 | 33.33% |
Al Viro | 4 | 3.54% | 1 | 33.33% |
Total | 113 | 100.00% | 3 | 100.00% |
/*
* MSS Values are chosen based on the 2011 paper
* 'An Analysis of TCP Maximum Segement Sizes' by S. Alcock and R. Nelson.
* Values ..
* .. lower than 536 are rare (< 0.2%)
* .. between 537 and 1299 account for less than < 1.5% of observed values
* .. in the 1300-1349 range account for about 15 to 20% of observed mss values
* .. exceeding 1460 are very rare (< 0.04%)
*
* 1460 is the single most frequently announced mss value (30 to 46% depending
* on monitor location). Table must be sorted.
*/
static __u16 const msstab[] = {
536,
1300,
1440, /* 1440, 1452: PPPoE */
1460,
};
/*
* Generate a syncookie. mssp points to the mss, which is returned
* rounded down to the value encoded in the cookie.
*/
u32 __cookie_v4_init_sequence(const struct iphdr *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);
}
Contributors
Person | Tokens | Prop | Commits | CommitProp |
Linus Torvalds (pre-git) | 57 | 60.64% | 2 | 40.00% |
Florian Westphal | 16 | 17.02% | 1 | 20.00% |
Arnaldo Carvalho de Melo | 12 | 12.77% | 1 | 20.00% |
Patrick McHardy | 9 | 9.57% | 1 | 20.00% |
Total | 94 | 100.00% | 5 | 100.00% |
EXPORT_SYMBOL_GPL(__cookie_v4_init_sequence);
__u32 cookie_v4_init_sequence(const struct sk_buff *skb, __u16 *mssp)
{
const struct iphdr *iph = ip_hdr(skb);
const struct tcphdr *th = tcp_hdr(skb);
return __cookie_v4_init_sequence(iph, th, mssp);
}
Contributors
Person | Tokens | Prop | Commits | CommitProp |
Arnaldo Carvalho de Melo | 20 | 42.55% | 1 | 25.00% |
Patrick McHardy | 17 | 36.17% | 1 | 25.00% |
Linus Torvalds (pre-git) | 9 | 19.15% | 1 | 25.00% |
Octavian Purdila | 1 | 2.13% | 1 | 25.00% |
Total | 47 | 100.00% | 4 | 100.00% |
/*
* Check if a ack sequence number is a valid syncookie.
* Return the decoded mss if it is, or 0 if not.
*/
int __cookie_v4_check(const struct iphdr *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;
}
Contributors
Person | Tokens | Prop | Commits | CommitProp |
Linus Torvalds (pre-git) | 42 | 57.53% | 2 | 40.00% |
Patrick McHardy | 19 | 26.03% | 1 | 20.00% |
Arnaldo Carvalho de Melo | 8 | 10.96% | 1 | 20.00% |
Florian Westphal | 4 | 5.48% | 1 | 20.00% |
Total | 73 | 100.00% | 5 | 100.00% |
EXPORT_SYMBOL_GPL(__cookie_v4_check);
struct sock *tcp_get_cookie_sock(struct sock *sk, struct sk_buff *skb,
struct request_sock *req,
struct dst_entry *dst)
{
struct inet_connection_sock *icsk = inet_csk(sk);
struct sock *child;
bool own_req;
child = icsk->icsk_af_ops->syn_recv_sock(sk, skb, req, dst,
NULL, &own_req);
if (child) {
atomic_set(&req->rsk_refcnt, 1);
sock_rps_save_rxhash(child, skb);
inet_csk_reqsk_queue_add(sk, req, child);
} else {
reqsk_free(req);
}
return child;
}
Contributors
Person | Tokens | Prop | Commits | CommitProp |
Linus Torvalds (pre-git) | 70 | 63.64% | 3 | 27.27% |
Eric Dumazet | 30 | 27.27% | 4 | 36.36% |
Arnaldo Carvalho de Melo | 8 | 7.27% | 3 | 27.27% |
David S. Miller | 2 | 1.82% | 1 | 9.09% |
Total | 110 | 100.00% | 11 | 100.00% |
EXPORT_SYMBOL(tcp_get_cookie_sock);
/*
* when syncookies are in effect and tcp timestamps are enabled we stored
* additional tcp options in the timestamp.
* This extracts these options from the timestamp echo.
*
* return false if we decode a tcp option that is disabled
* on the host.
*/
bool cookie_timestamp_decode(struct tcp_options_received *tcp_opt)
{
/* echoed timestamp, lowest bits contain options */
u32 options = tcp_opt->rcv_tsecr;
if (!tcp_opt->saw_tstamp) {
tcp_clear_options(tcp_opt);
return true;
}
if (!sysctl_tcp_timestamps)
return false;
tcp_opt->sack_ok = (options & TS_OPT_SACK) ? TCP_SACK_SEEN : 0;
if (tcp_opt->sack_ok && !sysctl_tcp_sack)
return false;
if ((options & TS_OPT_WSCALE_MASK) == TS_OPT_WSCALE_MASK)
return true; /* no window scaling */
tcp_opt->wscale_ok = 1;
tcp_opt->snd_wscale = options & TS_OPT_WSCALE_MASK;
return sysctl_tcp_window_scaling != 0;
}
Contributors
Person | Tokens | Prop | Commits | CommitProp |
Florian Westphal | 96 | 94.12% | 5 | 83.33% |
Vijay Subramanian | 6 | 5.88% | 1 | 16.67% |
Total | 102 | 100.00% | 6 | 100.00% |
EXPORT_SYMBOL(cookie_timestamp_decode);
bool cookie_ecn_ok(const struct tcp_options_received *tcp_opt,
const struct net *net, const struct dst_entry *dst)
{
bool ecn_ok = tcp_opt->rcv_tsecr & TS_OPT_ECN;
if (!ecn_ok)
return false;
if (net->ipv4.sysctl_tcp_ecn)
return true;
return dst_feature(dst, RTAX_FEATURE_ECN);
}
Contributors
Person | Tokens | Prop | Commits | CommitProp |
Florian Westphal | 59 | 100.00% | 2 | 100.00% |
Total | 59 | 100.00% | 2 | 100.00% |
EXPORT_SYMBOL(cookie_ecn_ok);
/* On input, sk is a listener.
* Output is listener if incoming packet would not create a child
* NULL if memory could not be allocated.
*/
struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
{
struct ip_options *opt = &TCP_SKB_CB(skb)->header.h4.opt;
struct tcp_options_received tcp_opt;
struct inet_request_sock *ireq;
struct tcp_request_sock *treq;
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 rtable *rt;
__u8 rcv_wscale;
struct flowi4 fl4;
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_v4_check(ip_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(skb, &tcp_opt, 0, NULL);
if (!cookie_timestamp_decode(&tcp_opt))
goto out;
ret = NULL;
req = inet_reqsk_alloc(&tcp_request_sock_ops, sk, false); /* for safety */
if (!req)
goto out;
ireq = inet_rsk(req);
treq = tcp_rsk(req);
treq->rcv_isn = ntohl(th->seq) - 1;
treq->snt_isn = cookie;
treq->ts_off = 0;
req->mss = mss;
ireq->ir_num = ntohs(th->dest);
ireq->ir_rmt_port = th->source;
sk_rcv_saddr_set(req_to_sk(req), ip_hdr(skb)->daddr);
sk_daddr_set(req_to_sk(req), ip_hdr(skb)->saddr);
ireq->ir_mark = inet_request_mark(sk, skb);
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.v64 = 0;
treq->tfo_listener = false;
ireq->ir_iif = inet_request_bound_dev_if(sk, skb);
/* We throwed the options of the initial SYN away, so we hope
* the ACK carries the same options again (see RFC1122 4.2.3.8)
*/
ireq->opt = tcp_v4_save_options(skb);
if (security_inet_conn_request(sk, skb, req)) {
reqsk_free(req);
goto out;
}
req->num_retrans = 0;
/*
* We need to lookup the route here to get at the correct
* window size. We should better make sure that the window size
* hasn't changed since we received the original syn, but I see
* no easy way to do this.
*/
flowi4_init_output(&fl4, ireq->ir_iif, ireq->ir_mark,
RT_CONN_FLAGS(sk), RT_SCOPE_UNIVERSE, IPPROTO_TCP,
inet_sk_flowi_flags(sk),
opt->srr ? opt->faddr : ireq->ir_rmt_addr,
ireq->ir_loc_addr, th->source, th->dest, sk->sk_uid);
security_req_classify_flow(req, flowi4_to_flowi(&fl4));
rt = ip_route_output_key(sock_net(sk), &fl4);
if (IS_ERR(rt)) {
reqsk_free(req);
goto out;
}
/* Try to redo what tcp_v4_send_synack did. */
req->rsk_window_clamp = tp->window_clamp ? :dst_metric(&rt->dst, RTAX_WINDOW);
tcp_select_initial_window(tcp_full_space(sk), req->mss,
&req->rsk_rcv_wnd, &req->rsk_window_clamp,
ireq->wscale_ok, &rcv_wscale,
dst_metric(&rt->dst, RTAX_INITRWND));
ireq->rcv_wscale = rcv_wscale;
ireq->ecn_ok = cookie_ecn_ok(&tcp_opt, sock_net(sk), &rt->dst);
ret = tcp_get_cookie_sock(sk, skb, req, &rt->dst);
/* ip_queue_xmit() depends on our flow being setup
* Normal sockets get it right from inet_csk_route_child_sock()
*/
if (ret)
inet_sk(ret)->cork.fl.u.ip4 = fl4;
out: return ret;
}
Contributors
Person | Tokens | Prop | Commits | CommitProp |
Linus Torvalds (pre-git) | 192 | 27.95% | 6 | 8.70% |
David S. Miller | 133 | 19.36% | 7 | 10.14% |
Eric Dumazet | 72 | 10.48% | 15 | 21.74% |
Arnaldo Carvalho de Melo | 59 | 8.59% | 6 | 8.70% |
Florian Westphal | 54 | 7.86% | 8 | 11.59% |
Linus Torvalds | 38 | 5.53% | 2 | 2.90% |
Paul Moore | 20 | 2.91% | 1 | 1.45% |
Lorenzo Colitti | 17 | 2.47% | 2 | 2.90% |
Cong Wang | 16 | 2.33% | 2 | 2.90% |
Laurent Chavey | 10 | 1.46% | 1 | 1.45% |
Jerry Chu | 10 | 1.46% | 2 | 2.90% |
Pavel Emelyanov | 10 | 1.46% | 1 | 1.45% |
Nikolay Borisov | 7 | 1.02% | 1 | 1.45% |
KOVACS Krisztian | 7 | 1.02% | 1 | 1.45% |
Al Viro | 7 | 1.02% | 2 | 2.90% |
David Ahern | 7 | 1.02% | 1 | 1.45% |
Venkat Yekkirala | 7 | 1.02% | 2 | 2.90% |
Patrick McHardy | 6 | 0.87% | 1 | 1.45% |
William Allen Simpson | 4 | 0.58% | 1 | 1.45% |
Yuchung Cheng | 4 | 0.58% | 2 | 2.90% |
Hideaki Yoshifuji / 吉藤英明 | 3 | 0.44% | 2 | 2.90% |
Denis V. Lunev | 2 | 0.29% | 1 | 1.45% |
Atis Elsts | 1 | 0.15% | 1 | 1.45% |
Dmitry Popov | 1 | 0.15% | 1 | 1.45% |
Total | 687 | 100.00% | 69 | 100.00% |
Overall Contributors
Person | Tokens | Prop | Commits | CommitProp |
Linus Torvalds (pre-git) | 396 | 23.96% | 8 | 8.60% |
Florian Westphal | 385 | 23.29% | 15 | 16.13% |
Matt Mackall | 219 | 13.25% | 1 | 1.08% |
David S. Miller | 135 | 8.17% | 7 | 7.53% |
Eric Dumazet | 108 | 6.53% | 18 | 19.35% |
Arnaldo Carvalho de Melo | 107 | 6.47% | 8 | 8.60% |
Patrick McHardy | 62 | 3.75% | 1 | 1.08% |
Linus Torvalds | 39 | 2.36% | 3 | 3.23% |
Al Viro | 35 | 2.12% | 2 | 2.15% |
Paul Moore | 20 | 1.21% | 1 | 1.08% |
Lorenzo Colitti | 17 | 1.03% | 2 | 2.15% |
Cong Wang | 16 | 0.97% | 2 | 2.15% |
Jason A. Donenfeld | 12 | 0.73% | 1 | 1.08% |
Hannes Frederic Sowa | 11 | 0.67% | 1 | 1.08% |
KOVACS Krisztian | 10 | 0.60% | 2 | 2.15% |
Pavel Emelyanov | 10 | 0.60% | 1 | 1.08% |
Laurent Chavey | 10 | 0.60% | 1 | 1.08% |
Jerry Chu | 10 | 0.60% | 2 | 2.15% |
Nikolay Borisov | 7 | 0.42% | 1 | 1.08% |
Venkat Yekkirala | 7 | 0.42% | 2 | 2.15% |
David Ahern | 7 | 0.42% | 1 | 1.08% |
Vijay Subramanian | 6 | 0.36% | 1 | 1.08% |
William Allen Simpson | 4 | 0.24% | 1 | 1.08% |
Yuchung Cheng | 4 | 0.24% | 2 | 2.15% |
Hideaki Yoshifuji / 吉藤英明 | 4 | 0.24% | 2 | 2.15% |
Andries E. Brouwer | 3 | 0.18% | 1 | 1.08% |
Paul Gortmaker | 3 | 0.18% | 1 | 1.08% |
Denis V. Lunev | 2 | 0.12% | 1 | 1.08% |
Atis Elsts | 1 | 0.06% | 1 | 1.08% |
Octavian Purdila | 1 | 0.06% | 1 | 1.08% |
Dmitry Popov | 1 | 0.06% | 1 | 1.08% |
Adrian Bunk | 1 | 0.06% | 1 | 1.08% |
Total | 1653 | 100.00% | 93 | 100.00% |
Information contained on this website is for historical information purposes only and does not indicate or represent copyright ownership.