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 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().

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.
>