2008-06-05 08:53:30

by Pavel Emelyanov

Subject: [PATCH 2/2] 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(-)

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

2008-06-05 17:19:56

by Serge E. Hallyn

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

Quoting Pavel Emelyanov ([email protected]):
> 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]>

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

-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

2008-06-05 19:17:32

by Serge E. Hallyn

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

Quoting Serge E. Hallyn ([email protected]):
> Quoting Pavel Emelyanov ([email protected]):
> > 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]>
>
> 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

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

-serge