Re: [PATCHv2 net 4/4] security: implement sctp_assoc_established hook in selinux

[Xin Long <lucien.xin@gmail.com>]

On Wed, Nov 3, 2021 at 1:33 PM Xin Long <lucien.xin@gmail.com> wrote:
>
> On Wed, Nov 3, 2021 at 12:40 PM Ondrej Mosnacek <omosnace@redhat.com> wrote:
> >
> > Hi Xin,
> >
> > On Tue, Nov 2, 2021 at 1:03 PM Xin Long <lucien.xin@gmail.com> wrote:
> > >
> > > Different from selinux_inet_conn_established(), it also gives the
> > > secid to asoc->peer_secid in selinux_sctp_assoc_established(),
> > > as one UDP-type socket may have more than one asocs.
> > >
> > > Note that peer_secid in asoc will save the peer secid for this
> > > asoc connection, and peer_sid in sksec will just keep the peer
> > > secid for the latest connection. So the right use should be do
> > > peeloff for UDP-type socket if there will be multiple asocs in
> > > one socket, so that the peeloff socket has the right label for
> > > its asoc.
> > >
> > > v1->v2:
> > >   - call selinux_inet_conn_established() to reduce some code
> > >     duplication in selinux_sctp_assoc_established(), as Ondrej
> > >     suggested.
> > >   - when doing peeloff, it calls sock_create() where it actually
> > >     gets secid for socket from socket_sockcreate_sid(). So reuse
> > >     SECSID_WILD to ensure the peeloff socket keeps using that
> > >     secid after calling selinux_sctp_sk_clone() for client side.
> >
> > Interesting... I find strange that SCTP creates the peeloff socket
> > using sock_create() rather than allocating it directly via
> > sock_alloc() like the other callers of sctp_copy_sock() (which calls
> > security_sctp_sk_clone()) do. Wouldn't it make more sense to avoid the
> > sock_create() call and just rely on the security_sctp_sk_clone()
> > semantic to set up the labels? Would anything break if
> > sctp_do_peeloff() switched to plain sock_alloc()?
> >
> > I'd rather we avoid this SECSID_WILD hack to support the weird
> > created-but-also-cloned socket hybrid and just make the peeloff socket
> > behave the same as an accept()-ed socket (i.e. no
> > security_socket_[post_]create() hook calls, just
> > security_sctp_sk_clone()).
>
> please check Paul's comment:
>
> """
>  The initial SCTP client association would
> need to take it's label from the parent process so perhaps that is the
> right answer for all SCTP client associations[2].
>
> [1] I would expect server side associations to follow the more
> complicated selinux_conn_sid() labeling, just as we do for TCP/stream
> connections today.
>
> [2] I'm guessing the client associations might also want to follow the
> setsockcreatecon(3) behavior, see selinux_sockcreate_sid() for more
> info.
> """
>
> That's what I got from it:
> For client side, secid should be copied from its parent socket directly, but
> get it from socket_sockcreate_sid().
For client side, secid should NOT be copied from its parent socket directly, but
gets it from socket_sockcreate_sid().
>
> and you?
>
> >
> > >
> > > Fixes: 72e89f50084c ("security: Add support for SCTP security hooks")
> > > Reported-by: Prashanth Prahlad <pprahlad@redhat.com>
> > > Reviewed-by: Richard Haines <richard_c_haines@btinternet.com>
> > > Tested-by: Richard Haines <richard_c_haines@btinternet.com>
> >
> > You made non-trivial changes since the last revision in this patch, so
> > you should have also dropped the Reviewed-by and Tested-by here. Now
> > David has merged the patches probably under the impression that they
> > have been reviewed/approved from the SELinux side, which isn't
> > completely true.
> Oh, that's a mistake, I thought I didn't add it.
> Will he be able to test this new patchset?
>
> Thanks.
>
> >
> > > Signed-off-by: Xin Long <lucien.xin@gmail.com>
> > > ---
> > >  security/selinux/hooks.c | 14 +++++++++++++-
> > >  1 file changed, 13 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> > > index a9977a2ae8ac..341cd5dccbf5 100644
> > > --- a/security/selinux/hooks.c
> > > +++ b/security/selinux/hooks.c
> > > @@ -5519,7 +5519,8 @@ static void selinux_sctp_sk_clone(struct sctp_association *asoc, struct sock *sk
> > >         if (!selinux_policycap_extsockclass())
> > >                 return selinux_sk_clone_security(sk, newsk);
> > >
> > > -       newsksec->sid = asoc->secid;
> > > +       if (asoc->secid != SECSID_WILD)
> > > +               newsksec->sid = asoc->secid;
> > >         newsksec->peer_sid = asoc->peer_secid;
> > >         newsksec->sclass = sksec->sclass;
> > >         selinux_netlbl_sctp_sk_clone(sk, newsk);
> > > @@ -5575,6 +5576,16 @@ static void selinux_inet_conn_established(struct sock *sk, struct sk_buff *skb)
> > >         selinux_skb_peerlbl_sid(skb, family, &sksec->peer_sid);
> > >  }
> > >
> > > +static void selinux_sctp_assoc_established(struct sctp_association *asoc,
> > > +                                          struct sk_buff *skb)
> > > +{
> > > +       struct sk_security_struct *sksec = asoc->base.sk->sk_security;
> > > +
> > > +       selinux_inet_conn_established(asoc->base.sk, skb);
> > > +       asoc->peer_secid = sksec->peer_sid;
> > > +       asoc->secid = SECSID_WILD;
> > > +}
> > > +
> > >  static int selinux_secmark_relabel_packet(u32 sid)
> > >  {
> > >         const struct task_security_struct *__tsec;
> > > @@ -7290,6 +7301,7 @@ static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = {
> > >         LSM_HOOK_INIT(sctp_assoc_request, selinux_sctp_assoc_request),
> > >         LSM_HOOK_INIT(sctp_sk_clone, selinux_sctp_sk_clone),
> > >         LSM_HOOK_INIT(sctp_bind_connect, selinux_sctp_bind_connect),
> > > +       LSM_HOOK_INIT(sctp_assoc_established, selinux_sctp_assoc_established),
> > >         LSM_HOOK_INIT(inet_conn_request, selinux_inet_conn_request),
> > >         LSM_HOOK_INIT(inet_csk_clone, selinux_inet_csk_clone),
> > >         LSM_HOOK_INIT(inet_conn_established, selinux_inet_conn_established),
> > > --
> > > 2.27.0
> > >
> >
> > --
> > Ondrej Mosnacek
> > Software Engineer, Linux Security - SELinux kernel
> > Red Hat, Inc.
> >