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syncookies: do not store rcv_wscale in tcp timestamp

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As pointed out by Fernando Gont there is no need to encode rcv_wscale
into the cookie.

We did not use the restored rcv_wscale anyway; it is recomputed
via tcp_select_initial_window().

Thus we can save 4 bits in the ts option space by removing rcv_wscale.
In case window scaling was not supported, we set the (invalid) wscale
value 0xf.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Florian Westphal 2010-06-21 11:48:44 +00:00 committed by David S. Miller
parent 9587c6ddd4
commit 734f614bc1
2 changed files with 14 additions and 22 deletions
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31
net/ipv4/syncookies.c
View File

@ -18,8 +18,8 @@
#include <net/tcp.h>
#include <net/route.h>
/* Timestamps: lowest 9 bits store TCP options */
#define TSBITS 9
/* Timestamps: lowest bits store TCP options */
#define TSBITS 5
#define TSMASK (((__u32)1 << TSBITS) - 1)
extern int sysctl_tcp_syncookies;
@ -58,7 +58,7 @@ static u32 cookie_hash(__be32 saddr, __be32 daddr, __be16 sport, __be16 dport,
/*
* when syncookies are in effect and tcp timestamps are enabled we encode
* tcp options in the lowest 9 bits of the timestamp value that will be
* 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.
@ -70,11 +70,9 @@ __u32 cookie_init_timestamp(struct request_sock *req)
u32 options = 0;
ireq = inet_rsk(req);
if (ireq->wscale_ok) {
options = ireq->snd_wscale;
options |= ireq->rcv_wscale << 4;
}
options |= ireq->sack_ok << 8;
options = ireq->wscale_ok ? ireq->snd_wscale : 0xf;
options |= ireq->sack_ok << 4;
ts = ts_now & ~TSMASK;
ts |= options;
@ -227,15 +225,14 @@ static inline struct sock *get_cookie_sock(struct sock *sk, struct sk_buff *skb,
* additional tcp options in the timestamp.
* This extracts these options from the timestamp echo.
*
* The lowest 4 bits are for snd_wscale
* The next 4 lsb are for rcv_wscale
* The lowest 4 bits store snd_wscale.
* The next lsb is for sack_ok
*
* return false if we decode an option that should not be.
*/
bool cookie_check_timestamp(struct tcp_options_received *tcp_opt)
{
/* echoed timestamp, 9 lowest bits contain options */
/* echoed timestamp, lowest bits contain options */
u32 options = tcp_opt->rcv_tsecr & TSMASK;
if (!tcp_opt->saw_tstamp) {
@ -246,21 +243,18 @@ bool cookie_check_timestamp(struct tcp_options_received *tcp_opt)
if (!sysctl_tcp_timestamps)
return false;
tcp_opt->snd_wscale = options & 0xf;
options >>= 4;
tcp_opt->rcv_wscale = options & 0xf;
tcp_opt->sack_ok = (options >> 4) & 0x1;
if (tcp_opt->sack_ok && !sysctl_tcp_sack)
return false;
if (tcp_opt->snd_wscale || tcp_opt->rcv_wscale) {
if ((options & 0xf) == 0xf)
return true; /* no window scaling */
tcp_opt->wscale_ok = 1;
tcp_opt->snd_wscale = options & 0xf;
return sysctl_tcp_window_scaling != 0;
}
return true;
}
EXPORT_SYMBOL(cookie_check_timestamp);
struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb,
@ -313,7 +307,6 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb,
ireq->rmt_addr = ip_hdr(skb)->saddr;
ireq->ecn_ok = 0;
ireq->snd_wscale = tcp_opt.snd_wscale;
ireq->rcv_wscale = tcp_opt.rcv_wscale;
ireq->sack_ok = tcp_opt.sack_ok;
ireq->wscale_ok = tcp_opt.wscale_ok;
ireq->tstamp_ok = tcp_opt.saw_tstamp;

1
net/ipv6/syncookies.c
View File

@ -217,7 +217,6 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
req->retrans = 0;
ireq->ecn_ok = 0;
ireq->snd_wscale = tcp_opt.snd_wscale;
ireq->rcv_wscale = tcp_opt.rcv_wscale;
ireq->sack_ok = tcp_opt.sack_ok;
ireq->wscale_ok = tcp_opt.wscale_ok;
ireq->tstamp_ok = tcp_opt.saw_tstamp;