netdev - Re: [PATCH net] ipv6: fix out of bound writes in __ip6_append

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Message-Id: <20170522.114834.59066499542253617.davem@davemloft.net>
Date:   Mon, 22 May 2017 11:48:34 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     eric.dumazet@...il.com
Cc:     andreyknvl@...gle.com, edumazet@...gle.com, idaifish@...il.com,
        netdev@...r.kernel.org
Subject: Re: [PATCH net] ipv6: fix out of bound writes in
 __ip6_append_data()

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Fri, 19 May 2017 14:17:48 -0700

> From: Eric Dumazet <edumazet@...gle.com>
> 
> Andrey Konovalov and idaifish@...il.com reported crashes caused by
> one skb shared_info being overwritten from __ip6_append_data()
> 
> Andrey program lead to following state :
> 
> copy -4200 datalen 2000 fraglen 2040 
> maxfraglen 2040 alloclen 2048 transhdrlen 0 offset 0 fraggap 6200
> 
> The skb_copy_and_csum_bits(skb_prev, maxfraglen, data + transhdrlen,
> fraggap, 0); is overwriting skb->head and skb_shared_info
> 
> Since we apparently detect this rare condition too late, move the
> code earlier to even avoid allocating skb and risking crashes.
> 
> Once again, many thanks to Andrey and syzkaller team.
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: Andrey Konovalov <andreyknvl@...gle.com>
> Tested-by: Andrey Konovalov <andreyknvl@...gle.com>
> Reported-by: <idaifish@...il.com>

Looks good, applied and queued up for -stable.

Thanks Eric.