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

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Date:   Wed, 8 May 2019 14:51:25 -0400
From:   Stephen Smalley <sds@...ho.nsa.gov>
To:     Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Cc:     Paolo Abeni <pabeni@...hat.com>, Paul Moore <paul@...l-moore.com>,
        selinux@...r.kernel.org, netdev@...r.kernel.org,
        Tom Deseyn <tdeseyn@...hat.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 2:27 PM, Marcelo Ricardo Leitner wrote:
> On Wed, May 08, 2019 at 02:13:17PM -0400, Stephen Smalley wrote:
>> 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.
> 
> Skipping the check would make it less controllable. So should it
> somehow re-use shutdown() stuff? It gets very confusing, and after
> all, it still is, in essence, a connect() syscall.

The function checks CONNECT permission on entry, before reaching this 
point.  This logic is only in preparation for a further check 
(NAME_CONNECT) on the port.  In this case, there is no further check to 
perform and we can just return.

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