devices cgroup: allow mkfifo

The devcgroup_inode_permission() hook in the devices whitelist cgroup has
always bypassed access checks on fifos.  But the mknod hook did not.  The
devices whitelist is only about block and char devices, and fifos can't
even be added to the whitelist, so fifos can't be created at all except by
tasks which have 'a' in their whitelist (meaning they have access to all
devices).

Fix the behavior by bypassing access checks to mkfifo.

Signed-off-by: Serge E. Hallyn <[email protected]>
Cc: Li Zefan <[email protected]>
Cc: Pavel Emelyanov <[email protected]>
Cc: Paul Menage <[email protected]>
Cc: Lai Jiangshan <[email protected]>
Cc: KOSAKI Motohiro <[email protected]>
Cc: James Morris <[email protected]>
Reported-by: Daniel Lezcano <[email protected]>
Cc: <[email protected]>		[2.6.27.x]
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

security/device_cgroup.c

@@ -513,6 +513,9 @@ int devcgroup_inode_mknod(int mode, dev_t dev)
 	struct dev_cgroup *dev_cgroup;
 	struct dev_whitelist_item *wh;
 
+	if (!S_ISBLK(mode) && !S_ISCHR(mode))
+		return 0;
+
 	rcu_read_lock();
 
 	dev_cgroup = task_devcgroup(current);