Re: [PATCH net] selinux: do not report error on connect(AF_UNSPEC)

[Paolo Abeni <pabeni@redhat.com>]

On Wed, 2019-05-08 at 17:17 -0400, Paul Moore wrote:
> On Wed, May 8, 2019 at 2:55 PM Stephen Smalley <sds@tycho.nsa.gov> wrote:
> > 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@redhat.com>
> > > > > > Signed-off-by: Paolo Abeni <pabeni@redhat.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.
> 
> I agree with Stephen, in the connect(AF_UNSPEC) case the right thing
> to do is to simply return with no error.

The 'default:' case is catching any address family other than
INET{4,6}, but I guess you argument still applies - selinux should not
do name check for unknown protocols ?!?

> I would also suggest that since this patch only touches the SELinux
> code it really should go in via the SELinux tree and not netdev; this
> will help avoid merge conflicts in the linux-next tree and during the
> merge window.  I think the right thing to do at this point is to
> create a revert patch (or have DaveM do it, I'm not sure what he
> prefers in situations like this) for this commit, make the adjustments
> that Stephen mentioned and submit them for the SELinux tree.

Sorry, my fault, I sent the email to both MLs for more awareness, I
should have used a different subject prefix.

@DaveM: if it's ok for you, I'll send a revert for this on netdev and
I'll send a v2 via the selinux ML, please let me know!

Thank you,

Paolo