Re: [PATCH] device_cgroup: fix unchecked cgroup parent usage

Andrew Morton
2012-10-31T23:35:06Z

On Wed, 31 Oct 2012 12:04:30 -0400
Aristeu Rozanski <aris@redhat.com> wrote:

> In 4cef7299b4786879a3e113e84084a72b24590c5b the cgroup parent usage is
> unchecked. root will not have a parent and trying to use
> device.{allow,deny} will cause problems.

>From my reading of the code "problems" means "kernel null pointer
dereference".

> For some reason my stressing
> scripts didn't test the root directory so I didn't catch it on my
> regular tests.
>
> --- github.orig/security/device_cgroup.c 2012-10-26 17:18:01.739366780 -0400
> +++ github/security/device_cgroup.c 2012-10-29 10:03:33.221918003 -0400
> @@ -352,6 +352,8 @@
> */
> static inline int may_allow_all(struct dev_cgroup *parent)

offtopic: this function could quite neatly have a bool return type.

> {
> + if (!parent)
> + return 1;

hm. Does it need a comment explaining what and why? I guess not... just.

> return parent->behavior == DEVCG_DEFAULT_ALLOW;
> }