netdev - Re: [PATCH bpf-next v3 09/15] bpf: add bpf_skc_to_udp6

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Date:   Tue, 23 Jun 2020 15:44:17 -0700
From:   Yonghong Song <yhs@...com>
To:     Eric Dumazet <eric.dumazet@...il.com>, <bpf@...r.kernel.org>,
        <netdev@...r.kernel.org>
CC:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>, <kernel-team@...com>,
        Martin KaFai Lau <kafai@...com>
Subject: Re: [PATCH bpf-next v3 09/15] bpf: add bpf_skc_to_udp6_sock() helper



On 6/23/20 3:11 PM, Eric Dumazet wrote:
> 
> 
> On 6/23/20 10:03 AM, Yonghong Song wrote:
>>
>>
>> On 6/23/20 9:27 AM, Eric Dumazet wrote:
>>>
>>>
>>> On 6/22/20 7:22 PM, Yonghong Song wrote:
>>>>
>>>>
>>>> On 6/22/20 6:47 PM, Eric Dumazet wrote:
>>> &
>>>>>
>>>>> Why is the sk_fullsock(sk) needed ?
>>>>
>>>> The parameter 'sk' could be a sock_common. That is why the
>>>> helper name bpf_skc_to_udp6_sock implies. The sock_common cannot
>>>> access sk_protocol, hence we requires sk_fullsock(sk) here.
>>>> Did I miss anything?
>>>
>>> OK, if arbitrary sockets can land here, you need also to check sk_type
>>
>> The current check is:
>>          if (sk_fullsock(sk) && sk->sk_protocol == IPPROTO_UDP &&
>>              sk->sk_family == AF_INET6)
>>                  return (unsigned long)sk;
>> it checks to ensure it is full socket, it is a ipv6 socket and then check protocol.
>>
>> Are you suggesting to add the following check?
>>    sk->sk_type == SOCK_DGRAM
>>
>> Not a networking expert. Maybe you can explain when we could have
>> protocol is IPPROTO_UDP and sk_type not SOCK_DGRAM?
> 
> 
> RAW sockets for instance.
> 
> Look at :
> 
> commit 940ba14986657a50c15f694efca1beba31fa568f
> Author: Eric Dumazet <edumazet@...gle.com>
> Date:   Tue Jan 21 23:17:14 2020 -0800
> 
>      gtp: make sure only SOCK_DGRAM UDP sockets are accepted
>      
>      A malicious user could use RAW sockets and fool
>      GTP using them as standard SOCK_DGRAM UDP sockets.

Thanks for the pointer! Will fix it in the next revision.