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 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 <[email protected]>

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

security/device_cgroup.c +16 -2

index f9941a7..baf3488 100644
@@ -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;
 }

Signature · 1 line

1.5.3.4

Quoted 11 lines · 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.

Quoted 8 lines

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 <[email protected]>

Acked-by Serge Hallyn <[email protected]>

Thanks. I suppose if it was deemed worth it, the other thing you could do would be to detect when you have a rule

c foo:bar r

and you add a rule

c foo:(all) r