cregit-Linux how code gets into the kernel

Release 4.8 net/ipv4/syncookies.c

Directory: net/ipv4
 *  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/cryptohash.h>
#include <linux/kernel.h>
#include <linux/export.h>
#include <net/tcp.h>
#include <net/route.h>

static u32 syncookie_secret[2][16-4+SHA_DIGEST_WORDS] __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 DEFINE_PER_CPU(__u32 [16 + 5 + SHA_WORKSPACE_WORDS], ipv4_cookie_scratch);

static u32 cookie_hash(__be32 saddr, __be32 daddr, __be16 sport, __be16 dport, u32 count, int c) { __u32 *tmp; net_get_random_once(syncookie_secret, sizeof(syncookie_secret)); tmp = this_cpu_ptr(ipv4_cookie_scratch); memcpy(tmp + 4, syncookie_secret[c], sizeof(syncookie_secret[c])); tmp[0] = (__force u32)saddr; tmp[1] = (__force u32)daddr; tmp[2] = ((__force u32)sport << 16) + (__force u32)dport; tmp[3] = count; sha_transform(tmp + 16, (__u8 *)tmp, tmp + 16 + 5); return tmp[17]; }


matt mackallmatt mackall10071.43%114.29%
al viroal viro2014.29%114.29%
hannes frederic sowahannes frederic sowa1410.00%114.29%
eric dumazeteric dumazet32.14%114.29%
tejun heotejun heo10.71%114.29%
florian westphalflorian westphal10.71%114.29%
christoph lameterchristoph lameter10.71%114.29%

/* * 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; }


florian westphalflorian westphal103100.00%4100.00%

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)); }


matt mackallmatt mackall6986.25%125.00%
florian westphalflorian westphal67.50%125.00%
al viroal viro45.00%125.00%
hideaki yoshifujihideaki yoshifuji11.25%125.00%

/* * 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 */ }


matt mackallmatt mackall10290.27%133.33%
florian westphalflorian westphal76.19%133.33%
al viroal viro43.54%133.33%

/* * 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); }


florian westphalflorian westphal1617.02%120.00%
arnaldo carvalho de meloarnaldo carvalho de melo1212.77%120.00%
patrick mchardypatrick mchardy99.57%120.00%

__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); }


arnaldo carvalho de meloarnaldo carvalho de melo2042.55%125.00%
patrick mchardypatrick mchardy1736.17%125.00%
octavian purdilaoctavian purdila12.13%125.00%

/* * 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; }


patrick mchardypatrick mchardy1926.03%120.00%
arnaldo carvalho de meloarnaldo carvalho de melo810.96%120.00%
florian westphalflorian westphal45.48%120.00%

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; }


eric dumazeteric dumazet3027.27%436.36%
arnaldo carvalho de meloarnaldo carvalho de melo87.27%327.27%
david s. millerdavid s. miller21.82%19.09%

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; }


florian westphalflorian westphal9694.12%583.33%
vijay subramanianvijay subramanian65.88%116.67%

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); }


florian westphalflorian westphal59100.00%2100.00%

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; 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 */ 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); 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; }


david s. millerdavid s. miller13319.65%710.45%
eric dumazeteric dumazet7210.64%1522.39%
arnaldo carvalho de meloarnaldo carvalho de melo598.71%68.96%
florian westphalflorian westphal487.09%710.45%
linus torvaldslinus torvalds385.61%22.99%
paul moorepaul moore202.95%11.49%
cong wangcong wang162.36%22.99%
lorenzo colittilorenzo colitti131.92%11.49%
pavel emelianovpavel emelianov101.48%11.49%
jerry chujerry chu101.48%22.99%
laurent chaveylaurent chavey101.48%11.49%
david aherndavid ahern71.03%11.49%
kovacs krisztiankovacs krisztian71.03%11.49%
nikolay borisovnikolay borisov71.03%11.49%
venkat yekkiralavenkat yekkirala71.03%22.99%
al viroal viro71.03%22.99%
patrick mchardypatrick mchardy60.89%11.49%
william allen simpsonwilliam allen simpson40.59%11.49%
yuchung chengyuchung cheng40.59%22.99%
hideaki yoshifujihideaki yoshifuji30.44%22.99%
denis v. lunevdenis v. lunev20.30%11.49%
dmitry popovdmitry popov10.15%11.49%
atis elstsatis elsts10.15%11.49%

Overall Contributors

florian westphalflorian westphal38121.98%1515.79%
matt mackallmatt mackall29416.96%11.05%
david s. millerdavid s. miller1357.79%77.37%
eric dumazeteric dumazet1237.10%1920.00%
arnaldo carvalho de meloarnaldo carvalho de melo1076.17%88.42%
patrick mchardypatrick mchardy623.58%11.05%
linus torvaldslinus torvalds392.25%33.16%
al viroal viro352.02%22.11%
paul moorepaul moore201.15%11.05%
cong wangcong wang160.92%22.11%
hannes frederic sowahannes frederic sowa160.92%11.05%
lorenzo colittilorenzo colitti130.75%11.05%
pavel emelianovpavel emelianov100.58%11.05%
laurent chaveylaurent chavey100.58%11.05%
jerry chujerry chu100.58%22.11%
kovacs krisztiankovacs krisztian100.58%22.11%
david aherndavid ahern70.40%11.05%
venkat yekkiralavenkat yekkirala70.40%22.11%
nikolay borisovnikolay borisov70.40%11.05%
vijay subramanianvijay subramanian60.35%11.05%
hideaki yoshifujihideaki yoshifuji40.23%22.11%
william allen simpsonwilliam allen simpson40.23%11.05%
yuchung chengyuchung cheng40.23%22.11%
tejun heotejun heo40.23%22.11%
paul gortmakerpaul gortmaker30.17%11.05%
andries brouwerandries brouwer30.17%11.05%
denis v. lunevdenis v. lunev20.12%11.05%
atis elstsatis elsts10.06%11.05%
adrian bunkadrian bunk10.06%11.05%
christoph lameterchristoph lameter10.06%11.05%
octavian purdilaoctavian purdila10.06%11.05%
dmitry popovdmitry popov10.06%11.05%
Directory: net/ipv4
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