netdev - Re: [PATCH] netlink: fix compat recvmsg

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Date:	Mon, 16 Aug 2010 15:01:28 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Johannes Berg <johannes@...solutions.net>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	Kalle Valo <kalle.valo@....fi>
Subject: Re: [PATCH] netlink: fix compat recvmsg

Le lundi 16 août 2010 à 14:50 +0200, Eric Dumazet a écrit :
> Le lundi 16 août 2010 à 09:20 +0200, Johannes Berg a écrit :
> > From: Johannes Berg <johannes.berg@...el.com>
> > 
> > Since
> > commit 1dacc76d0014a034b8aca14237c127d7c19d7726
> > Author: Johannes Berg <johannes@...solutions.net>
> > Date:   Wed Jul 1 11:26:02 2009 +0000
> > 
> >     net/compat/wext: send different messages to compat tasks
> > 
> > we had a race condition when setting and then
> > restoring frag_list. Eric attempted to fix it,
> > but the fix created even worse problems.
> > 
> > However, the original motivation I had when I
> > added the code that turned out to be racy is
> > no longer clear to me, since we only copy up
> > to skb->len to userspace, which doesn't include
> > the frag_list length. As a result, not doing
> > any frag_list clearing and restoring avoids
> > the race condition, while not introducing any
> > other problems.
> > 
> > Additionally, while preparing this patch I found
> > that since none of the remaining netlink code is
> > really aware of the frag_list, we need to use the
> > original skb's information for packet information
> > and credentials. This fixes, for example, the
> > group information received by compat tasks.
> > 
> > Cc: Eric Dumazet <eric.dumazet@...il.com>
> > Cc: stable@...nel.org [2.6.31+, for 2.6.35 revert 1235f504aa]
> > Signed-off-by: Johannes Berg <johannes.berg@...el.com>
> > ---
> 
> As a side effect, it might fix the 
> 
> 	if (nlk->flags & NETLINK_RECV_PKTINFO)
> 		netlink_cmsg_recv_pktinfo(msg, skb);
> 
> That tried to use pktinfo from the slave skb. After this
> patch, skb points to master skb.
> 

As you already mentioned it in your changelog, I missed it ;)



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