On Thu, 2012-12-06 at 17:36 -0200, Herton Ronaldo Krzesinski wrote: > On Mon, Dec 03, 2012 at 02:31:52PM +0000, Ben Hutchings wrote: > > 3.2-stable review patch. If anyone has any objections, please let me know. > > > > ------------------ > > > > From: Tejun Heo <[email protected]> > > > > commit 201e72acb2d3821e2de9ce6091e98859c316b29a upstream. > > > > dev_cgroup->exceptions is protected with devcgroup_mutex for writes > > and RCU for reads; however, RCU usage isn't correct. > > > > * dev_exception_clean() doesn't use RCU variant of list_del() and > > kfree(). The function can race with may_access() and may_access() > > may end up dereferencing already freed memory. Use list_del_rcu() > > and kfree_rcu() instead. > > > > * may_access() may be called only with RCU read locked but doesn't use > > RCU safe traversal over ->exceptions. Use list_for_each_entry_rcu(). > > > > Signed-off-by: Tejun Heo <[email protected]> > > Acked-by: Serge E. Hallyn <[email protected]> > > Cc: Aristeu Rozanski <[email protected]> > > Cc: Li Zefan <[email protected]> > > [bwh: Backported to 3.2: > > - Adjust context > > - Exception list is called whitelist] > > Signed-off-by: Ben Hutchings <[email protected]> > > I belive this backport is uneeded for 3.2 (or any stable <= 3.6), since > may_access_whitelist (may_access now in mainline) isn't called under > rcu_read_lock.
I think you're right. There are other readers that do rely on
rcu_read_lock(), but I don't think any of them can race with
devcgroup_destroy() (and if they can, it would have to use
kfree_rcu(dev_cgroup) as well).
You were too late for 3.2.35 but I'll revert this in the next update.
Ben.
> > ---
> > security/device_cgroup.c | 6 +++---
> > 1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > --- a/security/device_cgroup.c
> > +++ b/security/device_cgroup.c
> > @@ -202,8 +202,8 @@ static void devcgroup_destroy(struct cgr
> >
> > dev_cgroup = cgroup_to_devcgroup(cgroup);
> > list_for_each_entry_safe(wh, tmp, &dev_cgroup->whitelist, list) {
> > - list_del(&wh->list);
> > - kfree(wh);
> > + list_del_rcu(&wh->list);
> > + kfree_rcu(wh, rcu);
> > }
> > kfree(dev_cgroup);
> > }
> > @@ -278,7 +278,7 @@ static int may_access_whitelist(struct d
> > {
> > struct dev_whitelist_item *whitem;
> >
> > - list_for_each_entry(whitem, &c->whitelist, list) {
> > + list_for_each_entry_rcu(whitem, &c->whitelist, list) {
> > if (whitem->type & DEV_ALL)
> > return 1;
> > if ((refwh->type & DEV_BLOCK) && !(whitem->type & DEV_BLOCK))
> >
> >
> > --
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> >
>
--
Ben Hutchings
Computers are not intelligent. They only think they are.
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