netdev - Re: uninterruptible sleep in unix_dgram

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Message-Id: <20100308.124848.117951181.davem@davemloft.net>
Date:	Mon, 08 Mar 2010 12:48:48 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	mschmidt@...hat.com
Cc:	netdev@...r.kernel.org
Subject: Re: uninterruptible sleep in unix_dgram_recvmsg

From: Michal Schmidt <mschmidt@...hat.com>
Date: Thu, 4 Mar 2010 18:41:14 +0100

> So instead of that I started to think about why u->readlock is held
> across skb_recv_datagram() anyway. I found that it was added in 2.6.10
> by your patch "[AF_UNIX]: Serialize dgram read using semaphore just
> like stream" which apparently fixed an exploitable race condition
> (CAN-2004-1068).
> 
> I don't know what exactly u->readlock protects here.
> IOW, what race would this patch cause?:

Unfortunately I can't find any discussions about that change
and I can't find my own personal email archives from that far
back.

This is what irks me about handling security issues off-list
and in private.

In any event, I'm pretty sure we need to protect the dequeue
of SKBs from the datagram recv_queue with that mutex.  So
I'm weary to apply your patch.

Can you find a way to fix this without moving the SKB
dequeue outside of the lock?

Thanks.

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