netdev - Re: [PATCH net] selinux: do not report error on connect(AF

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Date:   Wed, 8 May 2019 14:13:17 -0400
From:   Stephen Smalley <sds@...ho.nsa.gov>
To:     Paolo Abeni <pabeni@...hat.com>, Paul Moore <paul@...l-moore.com>
Cc:     selinux@...r.kernel.org, netdev@...r.kernel.org,
        Tom Deseyn <tdeseyn@...hat.com>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        Richard Haines <richard_c_haines@...nternet.com>
Subject: Re: [PATCH net] selinux: do not report error on connect(AF_UNSPEC)

On 5/8/19 2:12 PM, Stephen Smalley wrote:
> On 5/8/19 9:32 AM, Paolo Abeni wrote:
>> calling connect(AF_UNSPEC) on an already connected TCP socket is an
>> established way to disconnect() such socket. After commit 68741a8adab9
>> ("selinux: Fix ltp test connect-syscall failure") it no longer works
>> and, in the above scenario connect() fails with EAFNOSUPPORT.
>>
>> Fix the above falling back to the generic/old code when the address 
>> family
>> is not AF_INET{4,6}, but leave the SCTP code path untouched, as it has
>> specific constraints.
>>
>> Fixes: 68741a8adab9 ("selinux: Fix ltp test connect-syscall failure")
>> Reported-by: Tom Deseyn <tdeseyn@...hat.com>
>> Signed-off-by: Paolo Abeni <pabeni@...hat.com>
>> ---
>>   security/selinux/hooks.c | 8 ++++----
>>   1 file changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
>> index c61787b15f27..d82b87c16b0a 100644
>> --- a/security/selinux/hooks.c
>> +++ b/security/selinux/hooks.c
>> @@ -4649,7 +4649,7 @@ static int selinux_socket_connect_helper(struct 
>> socket *sock,
>>           struct lsm_network_audit net = {0,};
>>           struct sockaddr_in *addr4 = NULL;
>>           struct sockaddr_in6 *addr6 = NULL;
>> -        unsigned short snum;
>> +        unsigned short snum = 0;
>>           u32 sid, perm;
>>           /* sctp_connectx(3) calls via selinux_sctp_bind_connect()
>> @@ -4674,12 +4674,12 @@ static int 
>> selinux_socket_connect_helper(struct socket *sock,
>>               break;
>>           default:
>>               /* Note that SCTP services expect -EINVAL, whereas
>> -             * others expect -EAFNOSUPPORT.
>> +             * others must handle this at the protocol level:
>> +             * connect(AF_UNSPEC) on a connected socket is
>> +             * a documented way disconnect the socket.
>>                */
>>               if (sksec->sclass == SECCLASS_SCTP_SOCKET)
>>                   return -EINVAL;
>> -            else
>> -                return -EAFNOSUPPORT;
> 
> I think we need to return 0 here.  Otherwise, we'll fall through with an 
> uninitialized snum, triggering a random/bogus permission check.

Sorry, I see that you initialize snum above.  Nonetheless, I think the 
correct behavior here is to skip the check since this is a disconnect, 
not a connect.

> 
>>           }
>>           err = sel_netport_sid(sk->sk_protocol, snum, &sid);
>>
>