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

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Date:   Tue, 23 Jun 2020 15:11:24 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Yonghong Song <yhs@...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 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.