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

[Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>]

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.

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