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

[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@openvz.org>

---
 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

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

[Serge E. Hallyn]

Quoting Pavel Emelyanov (xemul@openvz.org):
> 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@openvz.org>

Acked-by: Serge Hallyn <serue@us.ibm.com>

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

-serge

> ---
>  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

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

[Serge E. Hallyn]

Quoting Serge E. Hallyn (serue@us.ibm.com):
> Quoting Pavel Emelyanov (xemul@openvz.org):
> > 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@openvz.org>
> 
> Acked-by: Serge Hallyn <serue@us.ibm.com>
> 
> 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

But a private email response preferred the each-entry-is-separate
semantics, so I retract that suggestion.

-serge