From: Frederik Deweerdt <deweerdt@free•fr>
To: David Miller <davem@davemloft•net>
Cc: netdev@vger•kernel.org
Subject: Re: [Oops] unix_dgram_connect locking problem?
Date: Mon, 14 May 2007 20:49:08 +0200 [thread overview]
Message-ID: <20070514184908.GB3938@slug> (raw)
In-Reply-To: <20070514.032054.95058880.davem@davemloft.net>
Hi David,
On Mon, May 14, 2007 at 03:20:54AM -0700, David Miller wrote:
> From: Frederik Deweerdt <deweerdt@free•fr>
> Date: Fri, 11 May 2007 17:00:14 +0200
>
> > I think that not unix_state_rlock'ing "other" in
> > unix_dgram_connect may cause it to become NULL while passing it to
> > selinux_socket_unix_may_send. With the following patch applied, I've
> > seen no oops so far (1-2 hours as opposed to a few minutes before applying
> > the patch). Any thoughts?
>
> Thanks for this report and patch, similar code in UNIX stream connect
> has the following comment:
>
> /* Latch our state.
>
> It is tricky place. We need to grab write lock and cannot
> drop lock on peer. It is dangerous because deadlock is
> possible. Connect to self case and simultaneous
> attempt to connect are eliminated by checking socket
> state. other is TCP_LISTEN, if sk is TCP_LISTEN we
> check this before attempt to grab lock.
>
> Well, and we have to recheck the state after socket locked.
> */
> ...
> unix_state_wlock_nested(sk);
>
> So I think we need to be careful about deadlocks wrt. holding
> both wlock on sk and rlock on other at the same time in
> the dgram case too.
Thanks for your answer. I'll write and test a patch taking this into
account. I'm thinking to check if sk == other, in which case we don't
need to rlock. This is sufficient to avoid the deadlock case, isn't
it?. If yes, I wonder why the stream case has to resort to the sk_state?
Thanks,
Frederik
next prev parent reply other threads:[~2007-05-14 18:50 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-05-11 15:00 [Oops] unix_dgram_connect locking problem? Frederik Deweerdt
2007-05-14 10:20 ` David Miller
2007-05-14 18:49 ` Frederik Deweerdt [this message]
2007-05-31 22:22 ` David Miller
2007-06-01 11:34 ` Frederik Deweerdt
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