netdev - Re: [PATCH] net: drop dst before queueing fragments

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Message-Id: <20130417.011540.1594987403341413760.davem@davemloft.net>
Date:	Wed, 17 Apr 2013 01:15:40 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	tparkin@...alix.com, netdev@...r.kernel.org
Subject: Re: [PATCH] net: drop dst before queueing fragments

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Tue, 16 Apr 2013 15:55:41 -0700

> From: Eric Dumazet <edumazet@...gle.com>
> 
> Commit 4a94445c9a5c (net: Use ip_route_input_noref() in input path)
> added a bug in IP defragmentation handling, as non refcounted
> dst could escape an RCU protected section.
> 
> Commit 64f3b9e203bd068 (net: ip_expire() must revalidate route) fixed
> the case of timeouts, but not the general problem.
> 
> Tom Parkin noticed crashes in UDP stack and provided a patch,
> but further analysis permitted us to pinpoint the root cause.
> 
> Before queueing a packet into a frag list, we must drop its dst,
> as this dst has limited lifetime (RCU protected)
> 
> When/if a packet is finally reassembled, we use the dst of the very
> last skb, still protected by RCU and valid, as the dst of the
> reassembled packet.
> 
> Use same logic in IPv6, as there is no need to hold dst references.
> 
> Reported-by: Tom Parkin <tparkin@...alix.com>
> Tested-by: Tom Parkin <tparkin@...alix.com>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Applied.
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