netdev - Re: [PATCH bpf-next] flow_dissector: lookup netns by skb->sk if skb->dev is NULL

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Message-ID: <7e189586-4be0-1e2c-ed40-b676f2cf22db@gmail.com>
Date:   Wed, 26 Sep 2018 17:49:07 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Daniel Borkmann <daniel@...earbox.net>,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        netdev@...r.kernel.org
Cc:     ast@...nel.org, davem@...emloft.net,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH bpf-next] flow_dissector: lookup netns by skb->sk if
 skb->dev is NULL



On 09/25/2018 08:38 AM, Daniel Borkmann wrote:
> On 09/24/2018 10:49 PM, Willem de Bruijn wrote:
>> From: Willem de Bruijn <willemb@...gle.com>
>>
>> BPF flow dissectors are configured per network namespace.
>> __skb_flow_dissect looks up the netns through dev_net(skb->dev).
>>
>> In some dissector paths skb->dev is NULL, such as for Unix sockets.
>> In these cases fall back to looking up the netns by socket.
>>
>> Analyzing the codepaths leading to __skb_flow_dissect I did not find
>> a case where both skb->dev and skb->sk are NULL. Warn and fall back to
>> standard flow dissector if one is found.
>>
>> Fixes: d58e468b1112 ("flow_dissector: implements flow dissector BPF hook")
>> Reported-by: Eric Dumazet <edumazet@...gle.com>
>> Signed-off-by: Willem de Bruijn <willemb@...gle.com>
> 
> Applied to bpf-next, thanks Willem!
> 

Sadly lib/test_bpf should still cause crashes, because populate_skb()
populates an skb attached to a fake device, for which net pointer is NULL.