netdev - Re: [PATCH net-next-2.6] netlink: netlink

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Message-ID: <1281940276.3683.7.camel@jlt3.sipsolutions.net>
Date:	Mon, 16 Aug 2010 08:31:16 +0200
From:	Johannes Berg <johannes@...solutions.net>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH net-next-2.6] netlink: netlink_recvmsg() fix

On Mon, 2010-08-16 at 08:29 +0200, Eric Dumazet wrote:
> Le lundi 16 août 2010 à 08:22 +0200, Johannes Berg a écrit :
> > On Mon, 2010-08-16 at 08:10 +0200, Eric Dumazet wrote:
> > 
> > > We'll find another way to address the problem.
> > 
> > For my understanding: The problem is that the save/restore of the
> > frag_list skb can race so a second reader will not see the frag_list skb
> > because it gets there while it's NULL. This happens with MSG_PEEK, or
> > with clones of the SKB since skb_shared_info is invariant across clones.
> > 
> > Correct?
> > 
> 
> Yes
> 
> I believe we should have a mutual exclusion for the critical section.
> 
> (setting pointer to NULL, ...., setting pointer back to its orig value)

Yeah, that'd work, but I'm wondering now why I did this at all. The code
already restricts the data copying to skb->len, which will not include
the frag_list, so it should be OK to just leave it intact? I'll go and
look at that in more detail and try it.

johannes

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