netdev - Re: TCP-MD5 checksum failure on x86

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Date:	Mon, 17 May 2010 07:03:49 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Bijay Singh <Bijay.Singh@...vus.com>
Cc:	Stephen Hemminger <shemminger@...tta.com>,
	David Miller <davem@...emloft.net>,
	"<bhaskie@...il.com>" <bhaskie@...il.com>,
	"<bhutchings@...arflare.com>" <bhutchings@...arflare.com>,
	netdev <netdev@...r.kernel.org>,
	Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>
Subject: Re: TCP-MD5 checksum failure on x86_64 SMP

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@...vus.com>
Signed-off-by: Eric Dumazet <eric.dumazet@...il.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;


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