[PATCH 2/2] devscgroup: make white list more compact in some cases

[Pavel Emelyanov]

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 a
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@xxxxxxxxxx>

---
 security/device_cgroup.c |   18 ++++++++++++++++--
 1 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/security/device_cgroup.c b/security/device_cgroup.c
index f9941a7..baf3488 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;
 }
-- 
1.5.3.4

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