Re: TCP-MD5 checksum failure on x86_64 SMP

Eric Dumazet
2010-05-17T05:03:55Z

Le lundi 17 mai 2010 à 03:49 +0000, Bijay Singh a écrit :

> I am on quite an old kernel 2.6.27 and could not apply your patches.
>
> Then i moved on to the kernel 2.6.32.11 however since then I have not been able to bring up my card, this is something i need to fix before i can test you fix. Working on that.
>

Thanks again for the status report.

I see bug is older than what I stated in my previous mail

I could reproduce it in my lab and confirm following patch fixes it

This is a stable candidate (2.6.27 kernels)

Thanks

[PATCH] tcp: tcp_synack_options() fix

Commit 33ad798c924b4a (tcp: options clean up) introduced a problem
if MD5+SACK+timestamps were used in initial SYN message.

Some stacks (old linux for example) try to negotiate MD5+SACK+TSTAMP
sessions, but since 20 bytes of tcp options space are not enough to
store all the bits needed, we chose to disable timestamps in this case.

We send a SYN-ACK _without_ timestamp option, but socket has timestamps
enabled and all further outgoing messages contain a TS block, all with
the initial timestamp of the remote peer.

Fix is to really disable timestamps option for the whole session.

Reported-by: Bijay Singh <Bijay.Singh@guavus.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
---
net/ipv4/tcp_output.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 0dda86e..b8bb226 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -667,7 +667,7 @@ static unsigned tcp_synack_options(struct sock *sk,
u8 cookie_plus = (xvp != NULL && !xvp->cookie_out_never) ?
xvp->cookie_plus :
0;
- bool doing_ts = ireq->tstamp_ok;
+ bool doing_ts;

#ifdef CONFIG_TCP_MD5SIG
*md5 = tcp_rsk(req)->af_specific->md5_lookup(sk, req);
@@ -680,11 +680,12 @@ static unsigned tcp_synack_options(struct sock *sk,
* rather than TS in order to fit in better with old,
* buggy kernels, but that was deemed to be unnecessary.
*/
- doing_ts &= !ireq->sack_ok;
+ ireq->tstamp_ok &= !ireq->sack_ok;
}
#else
*md5 = NULL;
#endif
+ doing_ts = ireq->tstamp_ok;

/* We always send an MSS option. */
opts->mss = mss;