On Thu, Nov 29, 2012 at 07:29:45PM +0000, Serge E. Hallyn wrote:

quoted

Quoting Aristeu Rozanski (aris-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org):

quoted

In preparation for better hierarchy support, it's needed to retain the local
settings in order to try to reapply them after a propagated change if they're
still valid.

Cc: Tejun Heo <redacted>
Cc: Serge Hallyn <redacted>
Signed-off-by: Aristeu Rozanski <redacted>
 
---
 security/device_cgroup.c |  108 ++++++++++++++++++++++++++++++++++-------------
 1 file changed, 80 insertions(+), 28 deletions(-)

Hi,

thanks for doing this.  I've got one concern though.  I don't see
any place where devcgroup_create() was updated to create the
local exceptions list.  I think we need a guarantee that at

the local exceptions list is part of the dev_cgroup structure and it's
initialized on the patch 'device_cgroup: keep track of local group
setting':

@@ -190,6 +238,8 @@
        if (!dev_cgroup)
                return ERR_PTR(-ENOMEM);
        INIT_LIST_HEAD(&dev_cgroup->exceptions);
+       INIT_LIST_HEAD(&dev_cgroup->local.exceptions);
+       dev_cgroup->local.behavior = DEVCG_DEFAULT_NONE;
        parent_cgroup = cgroup->parent;

        if (parent_cgroup == NULL)

quoted

any time the local exceptions list will contain all the entries
contained in the cgroup->exceptions list.  Otherwise you cannot

hm, no. the local exceptions are meant to be used for stuff written
locally. the devcgroup->exceptions list is the list in effect.

quoted

use the exception_add() the way you do (or you can't use RCU),
since there could be a window between the successful addition
of a rule to cgroup->local.exceptions and the failed addition to
cgroup->exceptions, during which a task (since it won't need
the mutex for devcg_allow()) could exceed allowed permissions.

It's possible I'm misunderstanding.  If you think that's the case
just kick me and I'll take a fresh look.

I see your point. it's indeed a problem. in dev_exception_add(), it
needs to check for permissions before actually adding to
devcgroup->exceptions.

quoted

(Btw is there a git tree or gitweb view I could look at alongside
the patchset?)

I'll rebase the patchset along with a fix for this and resubmit with a
link to the git repo.