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From:   Paul Moore <paul@paul-moore.com>
Date:   Wed, 1 Mar 2023 13:48:57 -0500
Message-ID: <CAHC9VhTCwV2cGtBrjVYUKJ-ZETBQ-Pp_sk6mjKkkuH299zYh9g@mail.gmail.com>
Subject: Re: [PATCH testsuite 1/3] policy: make sure test_ibpkey_access_t can
 lock enough memory
To:     Ondrej Mosnacek <omosnace@redhat.com>
Cc:     Chris PeBenito <pebenito@ieee.org>, selinux@vger.kernel.org,
        Mimi Zohar <zohar@linux.ibm.com>,
        selinux-refpolicy@vger.kernel.org
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On Wed, Mar 1, 2023 at 10:21=E2=80=AFAM Ondrej Mosnacek <omosnace@redhat.co=
m> wrote:
> On Tue, Feb 28, 2023 at 5:51=E2=80=AFPM Paul Moore <paul@paul-moore.com> =
wrote:
> > On Tue, Feb 28, 2023 at 9:13=E2=80=AFAM Ondrej Mosnacek <omosnace@redha=
t.com> wrote:
> > >
> > > The ibv_create_cq() operation requires the caller to be able to lock
> > > enough memory (RLIMIT_MEMLOCK). In some environments (such as RHEL-8)
> > > the default resource limits may not be enough, requiring CAP_IPC_LOCK=
 to
> > > go above the limit. To make sure the test works also under stricter
> > > resource limits, grant CAP_IPC_LOCK to test_ibpkey_access_t.
> > >
> > > Reported-by: Mimi Zohar <zohar@linux.ibm.com>
> > > Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
> > > ---
> > >  policy/test_ibpkey.te | 2 ++
> > >  1 file changed, 2 insertions(+)
> > >
> > > diff --git a/policy/test_ibpkey.te b/policy/test_ibpkey.te
> > > index 863ff16..97f0c3c 100644
> > > --- a/policy/test_ibpkey.te
> > > +++ b/policy/test_ibpkey.te
> > > @@ -10,6 +10,8 @@ type test_ibpkey_access_t;
> > >  testsuite_domain_type(test_ibpkey_access_t)
> > >  typeattribute test_ibpkey_access_t ibpkeydomain;
> > >
> > > +allow test_ibpkey_access_t self:capability ipc_lock;
> >
> > FWIW, I brought this up back in 2019 and have been carrying a local
> > selinux-testsuite patch for this ever since (it's the only way to get
> > a clean run of the IB tests).  While it can be fixed in the
> > selinux-testsuite policy, I believe this is a more general problem and
> > should probably be fixed in refpol.
> >
> > https://lore.kernel.org/selinux/CAHC9VhTuYi+W0RukEV4WNrP5X_AFeouaWMsdbg=
xSL1v04mouWw@mail.gmail.com/
>
> I don't understand how you'd like this to be fixed in the system
> policy... I don't think there is any policy interface that would
> semantically match "any users of the SELinux IB hooks" or "callers of
> ibv_create_cq()" that we could stick the capability rule into. At
> least the testsuite policy doesn't use any such interface. Closest to
> it would be dev_rw_infiniband_dev(), but that doesn't seem like the
> right place.

Look at it this way, the selinux-testsuite is not doing anything
particularly unusual with respect to talking over IB; if the tests
need that permission it seems reasonable that normal IB users would
also need these permissions.

> Not to mention that the fact whether the capability is required or not
> depends on the resource limits imposed on the process. If its
> RLIMIT_MEMLOCK limit is sufficient, a process is perfectly able to
> create the cq without CAP_IPC_LOCK. Automatically granting it to all
> domains that use InfiniBand in some way "just in case" would
> potentially grant it also to domains that don't actually need it,
> violating the principle of least privilege.

Once again, the selinux-testsuite is not doing anything particularly
unusual so if we are hitting this it seems reasonable that other users
are hitting this as well.  If you're concerned about granting
CAP_IPC_LOCK you could always put it in a dedicated IB/RDMA refpol
interface as I believe this is just an issue with the IB/RDMA verb
interface involving CQs/QPs and not the underlying IB protocol layer.
Say something like "dev_rw_infiniband_rdma()"* which would call
"dev_rw_infiniband()"* and add the CAP_IPC_LOCK permission.

It would be good to hear Chris' take on this.

* Upstream refpol appears to have shortened the interface to
"dev_rw_infiniband()".

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