linux-kernel - Re: [PATCH V2 net] tuntap: properly align skb->head before building skb

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Message-Id: <06D9B61F-5C89-47C4-A060-B63FE5A8F922@gmail.com>
Date:   Sat, 28 Oct 2017 18:20:54 -0400
From:   Wei Wei <dotweiba@...il.com>
To:     David Miller <davem@...hat.com>
Cc:     jasowang@...hat.com, netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH V2 net] tuntap: properly align skb->head before building
 skb

With this patch, the crash can’t be reproduced with the syz-repro and crash log0/log1.

The auto-generated reproducers are here: 
https://github.com/dotweiba/skb_clone_atomic_inc_bug

Thanks,
Wei
> On 28 Oct 2017, at 6:06 AM, David Miller <davem@...hat.com> wrote:
> 
> From: Jason Wang <jasowang@...hat.com>
> Date: Fri, 27 Oct 2017 11:05:44 +0800
> 
>> An unaligned alloc_frag->offset caused by previous allocation will
>> result an unaligned skb->head. This will lead unaligned
>> skb_shared_info and then unaligned dataref which requires to be
>> aligned for accessing on some architecture. Fix this by aligning
>> alloc_frag->offset before the frag refilling.
>> 
>> Fixes: 0bbd7dad34f8 ("tun: make tun_build_skb() thread safe")
>> Cc: Eric Dumazet <edumazet@...gle.com>
>> Cc: Willem de Bruijn <willemdebruijn.kernel@...il.com>
>> Cc: Wei Wei <dotweiba@...il.com>
>> Cc: Dmitry Vyukov <dvyukov@...gle.com>
>> Cc: Mark Rutland <mark.rutland@....com>
>> Reported-by: Wei Wei <dotweiba@...il.com>
>> Signed-off-by: Jason Wang <jasowang@...hat.com>
> 
> Applied and queued up for -stable, thanks Jason.