On Tue, Jul 05, 2022 at 11:02:50PM +0200, Varad Gautam wrote:
> On Tue, Jul 5, 2022 at 6:18 PM Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
> >
> > On Tue, Jul 05, 2022 at 03:00:02PM +0000, Varad Gautam wrote:
> > > Check that a user-provided thermal state is within the maximum
> > > thermal states supported by a given driver before attempting to
> > > apply it. This prevents a subsequent OOB access in
> > > thermal_cooling_device_stats_update() while performing
> > > state-transition accounting on drivers that do not have this check
> > > in their set_cur_state() handle.
> > >
> > > Signed-off-by: Varad Gautam <varadgautam@xxxxxxxxxx>
> > > Cc: stable@xxxxxxxxxxxxxxx
> > > ---
> > > drivers/thermal/thermal_sysfs.c | 12 +++++++++++-
> > > 1 file changed, 11 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/thermal/thermal_sysfs.c b/drivers/thermal/thermal_sysfs.c
> > > index 1c4aac8464a7..0c6b0223b133 100644
> > > --- a/drivers/thermal/thermal_sysfs.c
> > > +++ b/drivers/thermal/thermal_sysfs.c
> > > @@ -607,7 +607,7 @@ cur_state_store(struct device *dev, struct device_attribute *attr,
> > > const char *buf, size_t count)
> > > {
> > > struct thermal_cooling_device *cdev = to_cooling_device(dev);
> > > - unsigned long state;
> > > + unsigned long state, max_state;
> > > int result;
> > >
> > > if (sscanf(buf, "%ld\n", &state) != 1)
> > > @@ -618,10 +618,20 @@ cur_state_store(struct device *dev, struct device_attribute *attr,
> > >
> > > mutex_lock(&cdev->lock);
> > >
> > > + result = cdev->ops->get_max_state(cdev, &max_state);
> > > + if (result)
> > > + goto unlock;
> > > +
> > > + if (state > max_state) {
> > > + result = -EINVAL;
> > > + goto unlock;
> > > + }
> > > +
> > > result = cdev->ops->set_cur_state(cdev, state);
> >
> > Why doesn't set_cur_state() check the max state before setting it? Why
> > are the callers forced to always check it before? That feels wrong...
> >
>
> The problem lies in thermal_cooling_device_stats_update(), not set_cur_state().
>
> If ->set_cur_state() doesn't error out on invalid state,
> thermal_cooling_device_stats_update() does a:
>
> stats->trans_table[stats->state * stats->max_states + new_state]++;
>
> stats->trans_table reserves space depending on max_states, but we'd end up
> reading/writing outside it. cur_state_store() can prevent this regardless of
> the driver's ->set_cur_state() implementation.
Why wouldn't cur_state_store() check for an out-of-bounds condition by
calling get_max_state() and then return an error if it is invalid,
preventing thermal_cooling_device_stats_update() from ever being called?
thanks,
greg k-h
