[PATCH] device_cgroup: fix unchecked cgroup parent usage

Aristeu Rozanski
2012-10-31T16:04:48Z

In 4cef7299b4786879a3e113e84084a72b24590c5b the cgroup parent usage is
unchecked. root will not have a parent and trying to use
device.{allow,deny} will cause problems. For some reason my stressing
scripts didn't test the root directory so I didn't catch it on my
regular tests.

Andrew, Tejun, this patch needs to make Linus tree ASAP or a revert for
4cef7299b4786879a3e113e84084a72b24590c5b.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Li Zefan <lizefan@huawei.com>
Cc: James Morris <jmorris@namei.org>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Serge Hallyn <serge.hallyn@canonical.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Aristeu Rozanski <aris@redhat.com>

--- 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)
{
+ if (!parent)
+ return 1;
return parent->behavior == DEVCG_DEFAULT_ALLOW;
}

@@ -376,11 +378,14 @@
int count, rc;
struct dev_exception_item ex;
struct cgroup *p = devcgroup->css.cgroup;
- struct dev_cgroup *parent = cgroup_to_devcgroup(p->parent);
+ struct dev_cgroup *parent = NULL;

if (!capable(CAP_SYS_ADMIN))
return -EPERM;

+ if (p->parent)
+ parent = cgroup_to_devcgroup(p->parent);
+
memset(&ex, 0, sizeof(ex));
b = buffer;

@@ -391,11 +396,14 @@
if (!may_allow_all(parent))
return -EPERM;
dev_exception_clean(devcgroup);
+ devcgroup->behavior = DEVCG_DEFAULT_ALLOW;
+ if (!parent)
+ break;
+
rc = dev_exceptions_copy(&devcgroup->exceptions,
&parent->exceptions);
if (rc)
return rc;
- devcgroup->behavior = DEVCG_DEFAULT_ALLOW;
break;
case DEVCG_DENY:
dev_exception_clean(devcgroup);