[libvirt] [PATCH V3] apparmor: support ptrace checks

[Christian Ehrhardt]

Hi Guido and everybody else,
Ubuntu had the feature that went into 4.13 for quite a while so I looked
into dropping our rules in favor of the upstream ones.
While doing so I found something yet unclear and filed [1] about it.

TL;DR: The rules "should" not work because they should also have a tracedby
rule, but they work.

Jjohansen will let us know when he has looked at it in detail.
The bug I mention here is to track that effort.

P.S. FYI There is something similar ahead for kernel 4.14 which will need a
similar rule for signals.

[1]: https://bugs.launchpad.net/ubuntu/+source/apparmor/+bug/1719471

On Mon, Sep 25, 2017 at 12:05 PM, Guido Günther <agx at sigxcpu.org> wrote:

> Hi,
> On Sun, Sep 24, 2017 at 02:26:01PM +0200, Guido Günther wrote:
> > Hi Jim,
> > On Fri, Sep 22, 2017 at 05:02:42PM -0600, Jim Fehlig wrote:
> > > Kernel 4.13 introduced finer-grained ptrace checks
> > >
> > > https://git.kernel.org/pub/scm/linux/kernel/git/stable/
> linux-stable.git/commit/?h=v4.13.2&id=290f458a4f16f9cf6cb6562b249e69
> fe1c3c3a07
> > >
> > > With kernel 4.13 and apparmor 2.11, simply starting libvirtd
> > > results in the following apparmor denial
> > >
> > > type=AVC msg=audit(1506112085.645:954): apparmor="DENIED"
> > > operation="ptrace" profile="/usr/sbin/libvirtd" pid=6984
> > > comm="libvirtd" requested_mask="trace" denied_mask="trace"
> > > peer="unconfined"
> > >
> > > Attempting to start an unconfined domain results in
> > >
> > > type=AVC msg=audit(1506112301.227:1112): apparmor="DENIED"
> > > operation="ptrace" profile="/usr/sbin/libvirtd" pid=7498
> > > comm="libvirtd" requested_mask="trace" denied_mask="trace"
> > > peer="/usr/sbin/libvirtd"
> > >
> > > And attempting to start a confined domain results in
> > >
> > > type=AVC msg=audit(1506112631.408:1312): apparmor="DENIED"
> > > operation="open" profile="virt-aa-helper" name="/etc/libnl/classid"
> > > pid=8283 comm="virt-aa-helper" requested_mask="r" denied_mask="r"
> > > fsuid=0 ouid=0
> > > type=AVC msg=audit(1506112631.530:1319): apparmor="DENIED"
> > > operation="open" profile="virt-aa-helper" name="/etc/libnl/classid"
> > > pid=8289 comm="virt-aa-helper" requested_mask="r" denied_mask="r"
> > > fsuid=0 ouid=0
> > > type=AVC msg=audit(1506112632.186:1324): apparmor="DENIED"
> > > operation="ptrace" profile="/usr/sbin/libvirtd" pid=8342
> > > comm="libvirtd" requested_mask="trace" denied_mask="trace"
> > > peer="libvirt-66154842-e926-4f92-92f0-1c1bf61dd1ff"
> > >
> > > Add ptrace rules to allow the trace operations.
> > >
> > > Resolves: https://bugzilla.suse.com/show_bug.cgi?id=1058847
> > > Signed-off-by: Jim Fehlig <jfehlig at suse.com>
> > > ---
> > >
> > > V3:
> > >  fix ptrace rule for per-domain profiles
> > >
> > > V2:
> > >  restrict ptrace permissions
> > >  drop support for dbus, signal, and unix
> > >
> > >  examples/apparmor/usr.sbin.libvirtd | 4 ++++
> > >  1 file changed, 4 insertions(+)
> > >
> > > diff --git a/examples/apparmor/usr.sbin.libvirtd
> b/examples/apparmor/usr.sbin.libvirtd
> > > index acb59e071..fa4ebb355 100644
> > > --- a/examples/apparmor/usr.sbin.libvirtd
> > > +++ b/examples/apparmor/usr.sbin.libvirtd
> > > @@ -37,6 +37,10 @@
> > >    network packet dgram,
> > >    network packet raw,
> > >
> > > +  ptrace (trace) peer=unconfined,
> > > +  ptrace (trace) peer=/usr/sbin/libvirtd,
> > > +  ptrace (trace) peer=libvirt-*,
> > > +
> >
> > This works here too! And I can even drop the first rule (ptrace (trace)
> > peer=unconfined) and things still work (and from reading the profile and
> > Jamies explanations it should work without it). Can you check if that
> > works for you too?  Otherwise:
> >
> > Reviewed-By: Guido Günther <agx at sigxcpu.org>
>
> I've pushed that patch as is since without the unconfined ptrace we're
> seeing denials with gnome-boxes and virsh.
> Cheers,
>  -- Guido
>
> >
> >
> > >    # Very lenient profile for libvirtd since we want to first focus on
> confining
> > >    # the guests. Guests will have a very restricted profile.
> > >    / r,
> > > --
> > > 2.14.1
> > >
> >
> > --
> > libvir-list mailing list
> > libvir-list at redhat.com
> > https://www.redhat.com/mailman/listinfo/libvir-list
> >
>
> --
> libvir-list mailing list
> libvir-list at redhat.com
> https://www.redhat.com/mailman/listinfo/libvir-list
>



-- 
Christian Ehrhardt
Software Engineer, Ubuntu Server
Canonical Ltd
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