[libvirt] [PATCH] apparmor: support finer-grained ptrace checks

[Jim Fehlig]

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=290f458a4f16f9cf6cb6562b249e69fe1c3c3a07

When Apparmor is enabled and libvirtd is confined, attempting to start
a domain fails

virsh start test
error: Failed to start domain test
error: internal error: child reported: Kernel does not provide mount
       namespace: Permission denied

The audit log contains

type=AVC msg=audit(1505466699.828:534): apparmor="DENIED"
operation="ptrace" profile="/usr/sbin/libvirtd" pid=6621
comm="libvirtd" requested_mask="trace" denied_mask="trace"
peer="/usr/sbin/libvirtd"

It was also noticed that simply connecting to libvirtd (e.g. virsh list)
resulted in the following entries in the audit log

type=AVC msg=audit(1505755799.975:65): apparmor="DENIED"
operation="ptrace" profile="/usr/sbin/libvirtd" pid=1418
comm="libvirtd" requested_mask="trace" denied_mask="trace"
peer="unconfined"
type=AVC msg=audit(1505755799.976:66): apparmor="DENIED"
operation="ptrace" profile="/usr/sbin/libvirtd" pid=1418
comm="libvirtd" requested_mask="trace" denied_mask="trace"
peer="unconfined"

Both Apparmor denials can be fixed by adding ptrace rules to the
libvirtd profile. The new rules only grant trace permission.

Resolves: https://bugzilla.suse.com/show_bug.cgi?id=1058847
Signed-off-by: Jim Fehlig <jfehlig at suse.com>
---

Even with debug enabled in libvirtd, I've had a hard time correlating a
libvirtd action that results in the denied ptrace check seen in the audit
log. I suspect it is related to accessing files in /proc as mentioned in
the apparmor wiki

http://wiki.apparmor.net/index.php/TechnicalDo_Proc_and_ptrace

cc'ing some of the usual apparmor suspects for any words of wisdom.

 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..ff84aa149 100644
--- a/examples/apparmor/usr.sbin.libvirtd
+++ b/examples/apparmor/usr.sbin.libvirtd
@@ -37,6 +37,10 @@
   network packet dgram,
   network packet raw,
 
+  # Support finer-grained ptrace checks, which were enabled in kernel 4.13
+  ptrace trace peer=/usr/sbin/libvirtd,
+  ptrace trace peer=unconfined,
+
   # 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