netdev - Re: [PATCH net] ipv4: frags: handle possible skb truesize change

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Message-Id: <20180731.144535.1317399050532306183.davem@davemloft.net>
Date:   Tue, 31 Jul 2018 14:45:35 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     edumazet@...gle.com
Cc:     netdev@...r.kernel.org, eric.dumazet@...il.com
Subject: Re: [PATCH net] ipv4: frags: handle possible skb truesize change

From: Eric Dumazet <edumazet@...gle.com>
Date: Mon, 30 Jul 2018 21:50:29 -0700

> ip_frag_queue() might call pskb_pull() on one skb that
> is already in the fragment queue.
> 
> We need to take care of possible truesize change, or we
> might have an imbalance of the netns frags memory usage.
> 
> IPv6 is immune to this bug, because RFC5722, Section 4,
> amended by Errata ID 3089 states :
> 
>   When reassembling an IPv6 datagram, if
>   one or more its constituent fragments is determined to be an
>   overlapping fragment, the entire datagram (and any constituent
>   fragments) MUST be silently discarded.
> 
> Fixes: 158f323b9868 ("net: adjust skb->truesize in pskb_expand_head()")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Applied and queued up for -stable.

Frankly, I think we should enforce the ipv6 rules for ipv4 too.

There is absolutely no reasonable situation where overlapping fragment
queue entries should arrive.  None whatsoever.