Re: [PATCH testsuite 1/3] policy: make sure test_ibpkey_access_t can lock enough memory

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On Wed, Mar 1, 2023 at 7:49 PM Paul Moore <paul@xxxxxxxxxxxxxx> wrote:
> On Wed, Mar 1, 2023 at 10:21 AM Ondrej Mosnacek <omosnace@xxxxxxxxxx> wrote:
> > On Tue, Feb 28, 2023 at 5:51 PM Paul Moore <paul@xxxxxxxxxxxxxx> wrote:
> > > On Tue, Feb 28, 2023 at 9:13 AM Ondrej Mosnacek <omosnace@xxxxxxxxxx> 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@xxxxxxxxxxxxx>
> > > > Signed-off-by: Ondrej Mosnacek <omosnace@xxxxxxxxxx>
> > > > ---
> > > >  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_AFeouaWMsdbgxSL1v04mouWw@xxxxxxxxxxxxxx/
> >
> > 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.

Okay, so I guess you addressed your comments more towards refpolicy
maintainer/contributors than to me as the submitter/testsuite
maintainer and I didn't have to react so defensively...

I agree that having better semantic interfaces for RDMA users in
refpolicy and Fedora policy would be nice, but I also wouldn't block
having a working testsuite on that. I'll be happy to switch any new
appropriate interfaces (and replicate them in Fedora policy) once they
are available.

>
> * Upstream refpol appears to have shortened the interface to
> "dev_rw_infiniband()".
>
> --
> paul-moore.com
>

--
Ondrej Mosnacek
Senior Software Engineer, Linux Security - SELinux kernel
Red Hat, Inc.





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