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

["Serge E. Hallyn" <serge-A9i7LUbDfNHQT0dZR+AlfA@public.gmane.org>]

Quoting Li Zefan (lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org):
> Serge Hallyn wrote:
> 
> > Quoting Amos Kong (akong-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org):
> >> @ 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.
> 
> 
> 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.

thanks,
-serge