netdev - Re: [PATCH net] ipv6: make icmp6_send() robust against null skb->dev

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Date:   Tue, 8 Jan 2019 12:41:32 +0100
From:   Piotr Sawicki <p.sawicki2@...tner.samsung.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Casey Schaufler <casey@...aufler-ca.com>,
        syzbot <syzkaller@...glegroups.com>
Subject: Re: [PATCH net] ipv6: make icmp6_send() robust against null
 skb->dev


On 1/8/19 12:14 PM, Eric Dumazet wrote:
> On Tue, Jan 8, 2019 at 3:08 AM Piotr Sawicki
> <p.sawicki2@...tner.samsung.com> wrote:
>
>> Yes I know.  It looks like the Smack's security rule was changed during this process.
>>
>> Firstly the packet was allowed to be received and it was put into the backlog queue. Then, the
>>
>> rule was changed, and during the release phase LSM was called again for the same packet.
>>
>> But this time, Smack denied access and tried to send an ICMPv6 packet to inform a peer.
>>
>> I want to make sure if it is the root cause of this problem.
>>
>>
>> Besides, what is the purpose of setting skb->dev to NULL in __sk_receive_skb() ?
>
> We can not keep a pointer to the device, the device might be
> dismantled/freed before socket backlog can be processed.
>
> Input processing is using RCU, meaning no refcount is taken on the device.

Thanks for explanation.