linux/net/ipv6/syncookies.c
Jerry Chu 9ad7c049f0 tcp: RFC2988bis + taking RTT sample from 3WHS for the passive open side
This patch lowers the default initRTO from 3secs to 1sec per
RFC2988bis. It falls back to 3secs if the SYN or SYN-ACK packet
has been retransmitted, AND the TCP timestamp option is not on.

It also adds support to take RTT sample during 3WHS on the passive
open side, just like its active open counterpart, and uses it, if
valid, to seed the initRTO for the data transmission phase.

The patch also resets ssthresh to its initial default at the
beginning of the data transmission phase, and reduces cwnd to 1 if
there has been MORE THAN ONE retransmission during 3WHS per RFC5681.

Signed-off-by: H.K. Jerry Chu <hkchu@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2011-06-08 17:05:30 -07:00

269 lines
7.4 KiB
C

/*
* 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
*
* 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/random.h>
#include <linux/cryptohash.h>
#include <linux/kernel.h>
#include <net/ipv6.h>
#include <net/tcp.h>
extern int sysctl_tcp_syncookies;
extern __u32 syncookie_secret[2][16-4+SHA_DIGEST_WORDS];
#define COOKIEBITS 24 /* Upper bits store count */
#define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1)
/* Table must be sorted. */
static __u16 const msstab[] = {
64,
512,
536,
1280 - 60,
1480 - 60,
1500 - 60,
4460 - 60,
9000 - 60,
};
/*
* This (misnamed) value is the age of syncookie which is permitted.
* Its ideal value should be dependent on TCP_TIMEOUT_INIT and
* sysctl_tcp_retries1. It's a rather complicated formula (exponential
* backoff) to compute at runtime so it's currently hardcoded here.
*/
#define COUNTER_TRIES 4
static inline struct sock *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;
child = icsk->icsk_af_ops->syn_recv_sock(sk, skb, req, dst);
if (child)
inet_csk_reqsk_queue_add(sk, req, child);
else
reqsk_free(req);
return child;
}
static DEFINE_PER_CPU(__u32 [16 + 5 + SHA_WORKSPACE_WORDS],
ipv6_cookie_scratch);
static u32 cookie_hash(const struct in6_addr *saddr, const struct in6_addr *daddr,
__be16 sport, __be16 dport, u32 count, int c)
{
__u32 *tmp = __get_cpu_var(ipv6_cookie_scratch);
/*
* we have 320 bits of information to hash, copy in the remaining
* 192 bits required for sha_transform, from the syncookie_secret
* and overwrite the digest with the secret
*/
memcpy(tmp + 10, syncookie_secret[c], 44);
memcpy(tmp, saddr, 16);
memcpy(tmp + 4, daddr, 16);
tmp[8] = ((__force u32)sport << 16) + (__force u32)dport;
tmp[9] = count;
sha_transform(tmp + 16, (__u8 *)tmp, tmp + 16 + 5);
return tmp[17];
}
static __u32 secure_tcp_syn_cookie(const struct in6_addr *saddr,
const struct in6_addr *daddr,
__be16 sport, __be16 dport, __u32 sseq,
__u32 count, __u32 data)
{
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 count,
__u32 maxdiff)
{
__u32 diff;
cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq;
diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS);
if (diff >= maxdiff)
return (__u32)-1;
return (cookie -
cookie_hash(saddr, daddr, sport, dport, count - diff, 1))
& COOKIEMASK;
}
__u32 cookie_v6_init_sequence(struct sock *sk, struct sk_buff *skb, __u16 *mssp)
{
const struct ipv6hdr *iph = ipv6_hdr(skb);
const struct tcphdr *th = tcp_hdr(skb);
int mssind;
const __u16 mss = *mssp;
tcp_synq_overflow(sk);
for (mssind = ARRAY_SIZE(msstab) - 1; mssind ; mssind--)
if (mss >= msstab[mssind])
break;
*mssp = msstab[mssind];
NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESSENT);
return secure_tcp_syn_cookie(&iph->saddr, &iph->daddr, th->source,
th->dest, ntohl(th->seq),
jiffies / (HZ * 60), mssind);
}
static inline int cookie_check(struct sk_buff *skb, __u32 cookie)
{
const struct ipv6hdr *iph = ipv6_hdr(skb);
const struct tcphdr *th = tcp_hdr(skb);
__u32 seq = ntohl(th->seq) - 1;
__u32 mssind = check_tcp_syn_cookie(cookie, &iph->saddr, &iph->daddr,
th->source, th->dest, seq,
jiffies / (HZ * 60), COUNTER_TRIES);
return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0;
}
struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
{
struct tcp_options_received tcp_opt;
u8 *hash_location;
struct inet_request_sock *ireq;
struct inet6_request_sock *ireq6;
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;
bool ecn_ok;
if (!sysctl_tcp_syncookies || !th->ack || th->rst)
goto out;
if (tcp_synq_no_recent_overflow(sk) ||
(mss = cookie_check(skb, cookie)) == 0) {
NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED);
goto out;
}
NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV);
/* check for timestamp cookie support */
memset(&tcp_opt, 0, sizeof(tcp_opt));
tcp_parse_options(skb, &tcp_opt, &hash_location, 0);
if (!cookie_check_timestamp(&tcp_opt, &ecn_ok))
goto out;
ret = NULL;
req = inet6_reqsk_alloc(&tcp6_request_sock_ops);
if (!req)
goto out;
ireq = inet_rsk(req);
ireq6 = inet6_rsk(req);
treq = tcp_rsk(req);
if (security_inet_conn_request(sk, skb, req))
goto out_free;
req->mss = mss;
ireq->rmt_port = th->source;
ireq->loc_port = th->dest;
ipv6_addr_copy(&ireq6->rmt_addr, &ipv6_hdr(skb)->saddr);
ipv6_addr_copy(&ireq6->loc_addr, &ipv6_hdr(skb)->daddr);
if (ipv6_opt_accepted(sk, skb) ||
np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo ||
np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) {
atomic_inc(&skb->users);
ireq6->pktopts = skb;
}
ireq6->iif = sk->sk_bound_dev_if;
/* So that link locals have meaning */
if (!sk->sk_bound_dev_if &&
ipv6_addr_type(&ireq6->rmt_addr) & IPV6_ADDR_LINKLOCAL)
ireq6->iif = inet6_iif(skb);
req->expires = 0UL;
req->retrans = 0;
ireq->ecn_ok = ecn_ok;
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 = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsecr : 0;
treq->rcv_isn = ntohl(th->seq) - 1;
treq->snt_isn = cookie;
/*
* 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;
ipv6_addr_copy(&fl6.daddr, &ireq6->rmt_addr);
final_p = fl6_update_dst(&fl6, np->opt, &final);
ipv6_addr_copy(&fl6.saddr, &ireq6->loc_addr);
fl6.flowi6_oif = sk->sk_bound_dev_if;
fl6.flowi6_mark = sk->sk_mark;
fl6.fl6_dport = inet_rsk(req)->rmt_port;
fl6.fl6_sport = inet_sk(sk)->inet_sport;
security_req_classify_flow(req, flowi6_to_flowi(&fl6));
dst = ip6_dst_lookup_flow(sk, &fl6, final_p, false);
if (IS_ERR(dst))
goto out_free;
}
req->window_clamp = tp->window_clamp ? :dst_metric(dst, RTAX_WINDOW);
tcp_select_initial_window(tcp_full_space(sk), req->mss,
&req->rcv_wnd, &req->window_clamp,
ireq->wscale_ok, &rcv_wscale,
dst_metric(dst, RTAX_INITRWND));
ireq->rcv_wscale = rcv_wscale;
ret = get_cookie_sock(sk, skb, req, dst);
out:
return ret;
out_free:
reqsk_free(req);
return NULL;
}