netdev - Re: [PATCH v2] socket: don't return uninitialized addresses on concurrent socket shutdown

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Message-ID: <20131116063956.GI26901@order.stressinduktion.org>
Date:	Sat, 16 Nov 2013 07:39:56 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	mpb <mpb.mail@...il.com>, netdev@...r.kernel.org
Subject: Re: [PATCH v2] socket: don't return uninitialized addresses on concurrent socket shutdown

On Fri, Nov 15, 2013 at 10:32:49PM -0800, Eric Dumazet wrote:
> On Sat, 2013-11-16 at 06:48 +0100, Hannes Frederic Sowa wrote:
> > If a blocking read waits on a socket which gets concurrently shut down we
> > return 0 as error and so indicate success to the socket functions which
> > thus copy an uninitialized stack allocated address back to the user.
> > Fix this by clearing the 128 byte size (on x86-64) address first.
> > 
> > This patch fixes the problem for recvfrom, recvmsg and recvmmsg.
> > 
> > Reported-by: mpb <mpb.mail@...il.com>
> > Signed-off-by: Hannes Frederic Sowa <hannes@...essinduktion.org>
> > ---
> 
> Are you clearing 128 bytes on every recvfrom() system call, just in case
> of this shutdown() issue ?

Yes, that gave me a bad feeling, too (so I explicitly mentioned it in the
changelog and hoped for some discussion).

> Can't we avoid this overhead ?
> 
> msg.msg_namelen should be set to 0 in this case.

I don't see how, currently. Either we tunnel a new return value through
->recvmsg or we use the address structure, mark it with a special AF_FOO and
check if we get back that same value.

I don't see how msg.msg_namelen set to zero can help?

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