Re: [libvirt] [PATCH] apparmor: allow qemu abstraction to read /proc/pid/cmdline
On 12/01/2017 06:26 AM, 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(a)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
Good point.
Would it be possible to use 'owner' match? Eg:
owner @{PROC}/@{pid}/cmdline r,
I still see the denial with 'owner'. I suppose that would only work if qemu is
invoked with libvirtd euid.
Either way, I think a comment is warranted above the rule stating it
is
an information leak.
How about the below squashed in? Or drop this patch and live with the denial? I
think the only side-affect is inability for qemu to report the signaling process
name.
Regards,
Jim
diff --git a/examples/apparmor/libvirt-qemu b/examples/apparmor/libvirt-qemu
index 3d9eed9ec..d4fad85a1 100644
--- a/examples/apparmor/libvirt-qemu
+++ b/examples/apparmor/libvirt-qemu
@@ -25,6 +25,9 @@
/dev/ptmx rw,
/dev/kqemu rw,
@{PROC}/*/status r,
+ # When qemu is signaled to terminate, it will read cmdline of signaling
+ # process for reporting purposes. Allowing read access to a process
+ # cmdline may leak sensitive information embedded in the cmdline.
@{PROC}/@{pid}/cmdline r,
# Per man(5) proc, the kernel enforces that a thread may
# only modify its comm value or those in its thread group.