devscgroup: make white list more compact in some cases

Consider you added a 'c foo:bar r' permission to some cgroup and then (a
bit later) 'c'foo:bar w' for it.  After this you'll see the

c foo:bar r
c foo:bar w

lines in a devices.list file.

Another example - consider you added 10 'c foo:bar r' permissions to some
cgroup (e.g.  by mistake).  After this you'll see 10 c foo:bar r lines in
a list file.

This is weird.  This situation also has one more annoying consequence.
Having many items in a white list makes permissions checking slower, sine
it has to walk a longer list.

The proposal is to merge permissions for items, that correspond to the
same device.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 16 insertions, 2 deletions

diff --git a/security/device_cgroup.c b/security/device_cgroup.c
index f9941a769738..baf348834b66 100644
--- a/security/device_cgroup.c
+++ b/security/device_cgroup.c
@@ -106,7 +106,7 @@ free_and_exit:
 static int dev_whitelist_add(struct dev_cgroup *dev_cgroup,
                         struct dev_whitelist_item *wh)
 {
-        struct dev_whitelist_item *whcopy;
+        struct dev_whitelist_item *whcopy, *walk;
 
         whcopy = kmalloc(sizeof(*whcopy), GFP_KERNEL);
         if (!whcopy)
@@ -114,7 +114,21 @@ static int dev_whitelist_add(struct dev_cgroup *dev_cgroup,
 
         memcpy(whcopy, wh, sizeof(*whcopy));
         spin_lock(&dev_cgroup->lock);
-        list_add_tail(&whcopy->list, &dev_cgroup->whitelist);
+        list_for_each_entry(walk, &dev_cgroup->whitelist, list) {
+                if (walk->type != wh->type)
+                        continue;
+                if (walk->major != wh->major)
+                        continue;
+                if (walk->minor != wh->minor)
+                        continue;
+
+                walk->access |= wh->access;
+                kfree(whcopy);
+                whcopy = NULL;
+        }
+
+        if (whcopy != NULL)
+                list_add_tail(&whcopy->list, &dev_cgroup->whitelist);
         spin_unlock(&dev_cgroup->lock);
         return 0;
 }