netdev - Re: [PATCH] tcp: Fix a connect() race with timewait sockets

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Date:	Wed, 02 Dec 2009 11:33:55 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
CC:	kdakhane@...il.com, netdev@...r.kernel.org,
	netfilter@...r.kernel.org, zbr@...emap.net
Subject: Re: [PATCH] tcp: Fix a connect() race with timewait sockets

Eric Dumazet a écrit :
> 
> But even if sysctl_tw_reuse is cleared, we might trigger the bug if
> local port is bound to a value.

Oh well, that's more subtle than that.

__inet_check_established() is called not only with bh disabled,
but also with a lock on bind list if twp != NULL.

However, if twp is NULL, lock is not held by caller.

[ Thats the final
  ret = check_established(death_row, sk, snum, NULL);
  in __inet_hash_connect()]

So triggering this bug with tw_reuse clear is tricky :

You need several threads, using sockets with REUSEADDR set,
and bind() to same address/port before connect() to same target.

We need another patch to correct this.

I wonder if always hold lock before calling check_established()
would be cleaner.

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