Re: Possible problem with e6afc8ac ("udp: remove headers from UDP packets before queueing")

From: Paul Moore <paul@paul-moore.com>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: samanthakumar@google.com, linux-security-module@vger.kernel.org,
	selinux@tycho.nsa.gov, netdev@vger.kernel.org,
	Stephen Smalley <sds@tycho.nsa.gov>
Subject: Re: Possible problem with e6afc8ac ("udp: remove headers from UDP packets before queueing")
Date: Thu, 2 Jun 2016 17:36:42 -0400	[thread overview]
Message-ID: <CAHC9VhQAiTRWMN-vNDXgAni2MhsyEYP8f2mZDY63xrx=5SxenQ@mail.gmail.com> (raw)
In-Reply-To: <0b1fde4f-57ef-8c5e-147f-10c4a51fb2b0@tycho.nsa.gov>

On Wed, Jun 1, 2016 at 4:44 PM, Stephen Smalley <sds@tycho.nsa.gov> wrote:
> On 06/01/2016 03:18 PM, Eric Dumazet wrote:
>> On Wed, 2016-06-01 at 15:01 -0400, Paul Moore wrote:
>>> Hello,
>>>
>>> I'm currently trying to debug a problem with 4.7-rc1 and labeled
>>> networking over UDP.  I'm having some difficulty with the latest
>>> 4.7-rc1 builds on my test system at the moment so I haven't been able
>>> to concisely identify the problem, but looking through the commits in
>>> 4.7-rc1 I think there may be a problem with the following:
>>>
>>>   commit e6afc8ace6dd5cef5e812f26c72579da8806f5ac
>>>   Author: samanthakumar <samanthakumar@google.com>
>>>   Date:   Tue Apr 5 12:41:15 2016 -0400
>>>
>>>    udp: remove headers from UDP packets before queueing
>>>
>>>    Remove UDP transport headers before queueing packets for reception.
>>>    This change simplifies a follow-up patch to add MSG_PEEK support.
>>>
>>>    Signed-off-by: Sam Kumar <samanthakumar@google.com>
>>>    Signed-off-by: Willem de Bruijn <willemb@google.com>
>>>    Signed-off-by: David S. Miller <davem@davemloft.net>
>>>
>>> ... it appears that this commit changes things so that sk_filter() is
>>> only called when sk->sk_filter is not NULL.  While this is fine for
>>> the traditional socket filter case, it causes problems with LSMs that
>>> make use of security_sock_rcv_skb() to enforce per-packet access
>>> controls.
>>>
>>> Hopefully I'll get 4.7-rc1 booting soon and I can do a proper
>>> bisection test around this patch, but I wanted to mention this now in
>>> case others are seeing the same problem.
>>
>> Thanks for the report. Please try following fix.
>>
>> sk_filter() got additional features like the skb_pfmemalloc() things and
>> security_sock_rcv_skb()
>
> This resolved the SELinux regression for me.
>
> Tested-by: Stephen Smalley <sds@tycho.nsa.gov>

The patch works for me too.  Eric, are you going to send this to DaveM
(assuming he isn't listening in on this thread and picking it up
himself)?

Tested-by: Paul Moore <paul@paul-moore.com>

>> diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
>> index d56c0559b477..0ff31d97d485 100644
>> --- a/net/ipv4/udp.c
>> +++ b/net/ipv4/udp.c
>> @@ -1618,12 +1618,12 @@ int udp_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
>>               }
>>       }
>>
>> -     if (rcu_access_pointer(sk->sk_filter)) {
>> -             if (udp_lib_checksum_complete(skb))
>> +     if (rcu_access_pointer(sk->sk_filter) &&
>> +         udp_lib_checksum_complete(skb))
>>                       goto csum_error;
>> -             if (sk_filter(sk, skb))
>> -                     goto drop;
>> -     }
>> +
>> +     if (sk_filter(sk, skb))
>> +             goto drop;
>>
>>       udp_csum_pull_header(skb);
>>       if (sk_rcvqueues_full(sk, sk->sk_rcvbuf)) {
>> diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
>> index 2da1896af934..f421c9f23c5b 100644
>> --- a/net/ipv6/udp.c
>> +++ b/net/ipv6/udp.c
>> @@ -653,12 +653,12 @@ int udpv6_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
>>               }
>>       }
>>
>> -     if (rcu_access_pointer(sk->sk_filter)) {
>> -             if (udp_lib_checksum_complete(skb))
>> -                     goto csum_error;
>> -             if (sk_filter(sk, skb))
>> -                     goto drop;
>> -     }
>> +     if (rcu_access_pointer(sk->sk_filter) &&
>> +         udp_lib_checksum_complete(skb))
>> +             goto csum_error;
>> +
>> +     if (sk_filter(sk, skb))
>> +             goto drop;
>>
>>       udp_csum_pull_header(skb);
>>       if (sk_rcvqueues_full(sk, sk->sk_rcvbuf)) {
>>
>>

-- 
paul moore
www.paul-moore.com