[libvirt] [PATCH] apparmor: allow qemu abstraction to read /proc/pid/cmdline

[Jim Fehlig]

On 12/04/2017 04:03 AM, Michal Privoznik wrote:
> On 12/01/2017 02:26 PM, Jamie Strandboge wrote:
>> On Thu, 2017-11-30 at 10:43 -0700, Jim Fehlig wrote:
>>> Noticed the following denial in audit.log when shutting down
>>> an apparmor confined domain
>>>
>>> type=AVC msg=audit(1512002299.742:131): apparmor="DENIED"
>>> operation="open" profile="libvirt-66154842-e926-4f92-92f0-
>>> 1c1bf61dd1ff"
>>> name="/proc/1475/cmdline" pid=2958 comm="qemu-system-x86"
>>> requested_mask="r" denied_mask="r" fsuid=469 ouid=0
>>>
>>> Squelch the denial by allowing read access to /proc/<pid>/cmdline.
>>>
>>> Signed-off-by: Jim Fehlig <jfehlig at suse.com>
>>> ---
>>>
>>> Note: In the audit.log snippet, PID 1475 is libvirtd and 2958 is the
>>> qemu process. I must admit it is not clear to me why
>>> /proc/<libvirtd-pid>/cmdline is read on domain shutdown.
>>>
>>>   examples/apparmor/libvirt-qemu | 1 +
>>>   1 file changed, 1 insertion(+)
>>>
>>> diff --git a/examples/apparmor/libvirt-qemu
>>> b/examples/apparmor/libvirt-qemu
>>> index 73bdbae87..3d9eed9ec 100644
>>> --- a/examples/apparmor/libvirt-qemu
>>> +++ b/examples/apparmor/libvirt-qemu
>>> @@ -25,6 +25,7 @@
>>>     /dev/ptmx rw,
>>>     /dev/kqemu rw,
>>>     @{PROC}/*/status r,
>>> +  @{PROC}/@{pid}/cmdline r,
>>
>> Note this is an information leak and allows reading potentially
>> sensitive information, such as passwords given on the command line. Eg:
>>
>> $ cat /proc/13335/cmdline | tr '\0' ' '
>> sh /tmp/testme --password=sensitive
> 
> Well, I'd say that passing passwords (or any sensitive information)
> through command line is doomed by definition. Anybody can read that
> (doing mere ps is enough).
> 
>>
>> Would it be possible to use 'owner' match? Eg:
>>
>>    owner @{PROC}/@{pid}/cmdline r,
> 
> Okay, this narrows the attack surface, but I guess that somebody else
> doing `ps' on the system will be able to obtain the password anyway.

Prefixing the rule with 'owner' didn't work as noted earlier in the thread

https://www.redhat.com/archives/libvir-list/2017-December/msg00031.html

I've pushed the patch with the comment squashed in, albeit dangerously close to 
the release :-).

Regards,
Jim