On Mon, Jan 06, 2020 at 11:18:11AM +0530, Viresh Kumar wrote:
> On 28-12-19, 14:43, qiwuchen55@xxxxxxxxx wrote:
> > From: chenqiwu <chenqiwu@xxxxxxxxxx>
> >
> > There is a potential UAF issue in xxx_cpufreq_reboot_notifier_evt() that
> > the cpufreq policy of cpu0 has been released before using it. So we should
> > make a judgement to avoid it.
>
> There is no UAF problem here, but that we do cpufreq_cpu_get() with a
> corresponding cpufreq_cpu_put().
>
> > Signed-off-by: chenqiwu <chenqiwu@xxxxxxxxxx>
> > ---
> > drivers/cpufreq/s3c2416-cpufreq.c | 11 ++++++++++-
> > drivers/cpufreq/s5pv210-cpufreq.c | 10 +++++++++-
> > 2 files changed, 19 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/cpufreq/s3c2416-cpufreq.c b/drivers/cpufreq/s3c2416-cpufreq.c
> > index 1069103..0f576ba 100644
> > --- a/drivers/cpufreq/s3c2416-cpufreq.c
> > +++ b/drivers/cpufreq/s3c2416-cpufreq.c
> > @@ -304,6 +304,7 @@ static int s3c2416_cpufreq_reboot_notifier_evt(struct notifier_block *this,
> > {
> > struct s3c2416_data *s3c_freq = &s3c2416_cpufreq;
> > int ret;
> > + struct cpufreq_policy policy;
> >
> > mutex_lock(&cpufreq_lock);
> >
> > @@ -318,7 +319,15 @@ static int s3c2416_cpufreq_reboot_notifier_evt(struct notifier_block *this,
> > */
> > if (s3c_freq->is_dvs) {
> > pr_debug("cpufreq: leave dvs on reboot\n");
> > - ret = cpufreq_driver_target(cpufreq_cpu_get(0), FREQ_SLEEP, 0);
> > +
> > + memset(&policy, 0, sizeof(policy));
> > + ret = cpufreq_get_policy(&policy, 0);
> > + if (ret < 0) {
> > + pr_debug("cpufreq: get no policy for cpu0\n");
> > + return NOTIFY_BAD;
> > + }
> > +
>
> This doesn't make sense to me, why don't you do cpufreq_cpu_get() and
> put() instead ?
>
Hi viresh,
I can't explain which approach is better, but I think both approaches are
effective for the situation.
By the way, there is a possibility that the cpu0 hotplug thread will call
cpufreq_policy_free() to free cpufreq policy if cpu0 hotplug failed.
I think there should be a judgement to avoid this UAF risk if necessary,
or we just do panic if cpu0's cpufreq policy is free.
> > + ret = cpufreq_driver_target(&policy, FREQ_SLEEP, 0);
> > if (ret < 0)
> > return NOTIFY_BAD;
> > }
> > diff --git a/drivers/cpufreq/s5pv210-cpufreq.c b/drivers/cpufreq/s5pv210-cpufreq.c
> > index 5d10030..d99b4b1 100644
> > --- a/drivers/cpufreq/s5pv210-cpufreq.c
> > +++ b/drivers/cpufreq/s5pv210-cpufreq.c
> > @@ -555,8 +555,16 @@ static int s5pv210_cpufreq_reboot_notifier_event(struct notifier_block *this,
> > unsigned long event, void *ptr)
> > {
> > int ret;
> > + struct cpufreq_policy *policy;
> >
> > - ret = cpufreq_driver_target(cpufreq_cpu_get(0), SLEEP_FREQ, 0);
> > + policy = cpufreq_cpu_get(0);
> > + if (!policy) {
> > + pr_debug("cpufreq: get no policy for cpu0\n");
> > + return NOTIFY_BAD;
> > + }
> > +
> > + ret = cpufreq_driver_target(policy, SLEEP_FREQ, 0);
> > + cpufreq_cpu_put(policy);
>
> Like what is done here.
>
> Also add a blank line here.
>
> > if (ret < 0)
> > return NOTIFY_BAD;
> >
> > --
> > 1.9.1
>
> --
> viresh
Thanks for your review!
Qiwu
