Re: [PATCH] cgroup: fix device deny of DEV_ALL

[Amos Kong]

On 22/05/12 09:54, Serge E. Hallyn wrote:
> Quoting Li Zefan (lizefan@xxxxxxxxxx):
> > Serge Hallyn wrote:
> >
> > > Quoting Amos Kong (akong@xxxxxxxxxx):
> > > > @ mount -t cgroup -o devices none /cgroup
> > > > @ mkdir /cgroups/devices
> > > > @ ls -l /dev/dm-3
> > > >   brw-rw----. 1 root disk 253, 3 Oct 14 19:03 /dev/dm-3
> > > > @ echo 'b 253:3 rw'>  devices.deny
> > > > but I can still write it by 'dd if=/dev/zero of=/dev/dm-3'
> > > >
> > > > In devcgroup_create(), we create a new whitelist, and add first
> > > > entry which type is 'DEV_ALL'. Execute "# echo 'b 253:3 rw'>
> > > > devices.deny", dev_whitelist_rm() will update access of first
> > > > entry to 1(m), but type of first entry is still 'DEV_ALL'.
> > >
> > > Hi,
> > >
> > > thanks.  You raise a good point, but I think it needs some discussion.
> > >
> > > What happens right now is that if you have the 'a *:* rwm' entry and do
> > > echo 'b 253:3 rw'>  devices.deny, then when you next cat devices.list you
> > > will still see the 'a *:* rwm' entry.  So there should be no confusion
> > > over why the dd succeeds.

> > >   You didn't remove the entry, because there
> > > was no match echoed into devices.deny.

Hi serge,

My patch updated type,major,minor, it _equals to_ remove 'a *:* rwm' and 
add 'b *:* m'
It's a clear logic, why need to manually remove 'a *:* rwm'?


> > No, you'll see the entry has been changed to 'a *:* m', so I think we
> > should at least fix this.
>
> Yikes.  Agreed.  That's a bug.

which bug? should not update walk->access if wh->access is not 'rwm'?

diff --git a/security/device_cgroup.c b/security/device_cgroup.c
index c43a332..e619a34 100644
--- a/security/device_cgroup.c
+++ b/security/device_cgroup.c
@@ -145,7 +145,8 @@ static void dev_whitelist_rm(struct dev_cgroup 
*dev_cgroup,
                        continue;

 remove:
-               walk->access &= ~wh->access;
+               if (walk->type != DEV_ALL || wh->access == ACC_MASK)
+                       walk->access &= ~wh->access;
                if (!walk->access) {
                        list_del_rcu(&walk->list);
                        kfree_rcu(walk, rcu);


--
			Amos.
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