netdev - Re: [PATCH net 2/2] net: fix sock_wake

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Date:	Tue, 01 Dec 2015 15:45:29 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	edumazet@...gle.com
Cc:	netdev@...r.kernel.org, dvyukov@...gle.com,
	hannes@...essinduktion.org, edumazet@...il.com
Subject: Re: [PATCH net 2/2] net: fix sock_wake_async() rcu protection

From: Eric Dumazet <edumazet@...gle.com>
Date: Sun, 29 Nov 2015 20:03:11 -0800

> Dmitry provided a syzkaller (http://github.com/google/syzkaller)
> triggering a fault in sock_wake_async() when async IO is requested.
> 
> Said program stressed af_unix sockets, but the issue is generic
> and should be addressed in core networking stack.
> 
> The problem is that by the time sock_wake_async() is called,
> we should not access the @flags field of 'struct socket',
> as the inode containing this socket might be freed without
> further notice, and without RCU grace period.
> 
> We already maintain an RCU protected structure, "struct socket_wq"
> so moving SOCKWQ_ASYNC_NOSPACE & SOCKWQ_ASYNC_WAITDATA into it
> is the safe route.
> 
> It also reduces number of cache lines needing dirtying, so might
> provide a performance improvement anyway.
> 
> In followup patches, we might move remaining flags (SOCK_NOSPACE,
> SOCK_PASSCRED, SOCK_PASSSEC) to save 8 bytes and let 'struct socket'
> being mostly read and let it being shared between cpus.
> 
> Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Applied and queued up for -stable.
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