On Thu, Jan 31, 2013 at 04:19:32AM +0000, Serge E. Hallyn wrote:
> Quoting [email protected] ([email protected]):
> > +/**
> > + * propagate_behavior - propagates a change in the behavior down in
> > hierarchy
> > + * @devcg_root: device cgroup that changed behavior
> > + *
> > + * returns: 0 in case of success, != 0 in case of error
> > + *
> > + * This is one of the two key functions for hierarchy implementation.
> > + * All cgroup's children recursively will have the behavior changed and
> > + * exceptions copied from the parent then its local behavior and exceptions
> > + * re-evaluated and applied if they're still allowed. Refer to
> > + * Documentation/cgroups/devices.txt for more details.
> > + */
> > +static int propagate_behavior(struct dev_cgroup *devcg_root)
> > +{
> > + struct cgroup *root = devcg_root->css.cgroup;
> > + struct dev_cgroup *parent, *devcg, *tmp;
> > + int rc = 0;
> > + LIST_HEAD(pending);
> > +
> > + get_online_devcg(root, &pending);
> > +
> > + list_for_each_entry_safe(devcg, tmp, &pending, propagate_pending) {
> > + parent = cgroup_to_devcgroup(devcg->css.cgroup->parent);
> > +
> > + /* first copy parent's state */
> > + devcg->behavior = parent->behavior;
> > + dev_exception_clean(&devcg->exceptions);
> > + rc = dev_exceptions_copy(&devcg->exceptions,
> > &parent->exceptions);
> > + if (rc) {
> > + devcg->behavior = DEVCG_DEFAULT_DENY;
> > + break;
> > + }
> > +
> > + if (devcg->local.behavior == DEVCG_DEFAULT_DENY &&
> > + devcg->behavior == DEVCG_DEFAULT_ALLOW) {
> > + devcg->behavior = DEVCG_DEFAULT_DENY;
> > + }
>
> I think you might need another special case here. If A and it's
> child B are both ALLOW, and A switches to DENY, then if I read this
> right B will be switched to DENY, but its local->exceptions will
> not be cleared. They won't be immediately applied, so at first it's
> ok. But if B then adds an exception, what happens? It'll call
> revalidate_exceptions on the full old list plus new exception. If
> any exceptions aren't allowed by the parent then it won't be applied,
> but it's possible that it is allowed in the parent but (its sense
> now being inverted from blacklist to whitelist) not intended to be
> allowed in the child. But there will be nothing to stop it.
>
> So do you need
>
> if (devcg->local.behavior == DEVCG_DEFAULT_ALLOW &&
> devcg->behavior == DEVCG_DEFAULT_DENY) {
> dev_exception_clean(&devcg->local.exceptions);
> }
>
> here?
>
> > + if (devcg->local.behavior == devcg->behavior)
> > + rc = revalidate_exceptions(devcg);
I think:
else
dev_exception_clean(&devcg->local.exceptions);
here instead
--
Aristeu
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