Re: [PATCH v2] cpufreq: s3c: avoid use after free issue in xxx_cpufreq_reboot_notifier_evt()

[chenqiwu <qiwuchen55@gmail.com>]

On Tue, Jan 07, 2020 at 11:01:47AM +0530, Viresh Kumar wrote:
> On 06-01-20, 17:44, qiwuchen55@gmail.com wrote:
> > From: chenqiwu <chenqiwu@xiaomi.com>
> > 
> > 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.
> 
> Again, the subject and description are incorrect here. This isn't a user after
> free problem as we were already calling cpufreq_cpu_get(). The problem was that
> the balancing of refcount wasn't done properly.
> 
>

Yeah, I will rewrite the title and commit message, and resend this as
patch v3.

Thanks!

> > Signed-off-by: chenqiwu <chenqiwu@xiaomi.com>
> > ---
> > changes in v2:
> >  - use the combination of cpufreq_cpu_get() and cpufreq_cpu_put()
> >    instead of cpufreq_get_policy() in s3c2416-cpufreq.c
> > ---
> >  drivers/cpufreq/s3c2416-cpufreq.c | 12 +++++++++++-
> >  drivers/cpufreq/s5pv210-cpufreq.c | 11 ++++++++++-
> >  2 files changed, 21 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/cpufreq/s3c2416-cpufreq.c b/drivers/cpufreq/s3c2416-cpufreq.c
> > index 1069103..f07c5d1 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 +319,16 @@ 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);
> > +
> > +		policy = cpufreq_cpu_get(0);
> > +		if (!policy) {
> > +			pr_debug("cpufreq: get no policy for cpu0\n");
> > +			return NOTIFY_BAD;
> > +		}
> > +
> > +		ret = cpufreq_driver_target(&policy, FREQ_SLEEP, 0);
> > +		cpufreq_cpu_put(policy);
> > +
> >  		if (ret < 0)
> >  			return NOTIFY_BAD;
> >  	}
> > diff --git a/drivers/cpufreq/s5pv210-cpufreq.c b/drivers/cpufreq/s5pv210-cpufreq.c
> > index 5d10030..e84281e 100644
> > --- a/drivers/cpufreq/s5pv210-cpufreq.c
> > +++ b/drivers/cpufreq/s5pv210-cpufreq.c
> > @@ -555,8 +555,17 @@ static int s5pv210_cpufreq_reboot_notifier_event(struct notifier_block *this,
> >  						 unsigned long event, void *ptr)
> >  {
> >  	int ret;
> > +	struct cpufreq_policy *policy;
> > +
> > +	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);
> >  
> > -	ret = cpufreq_driver_target(cpufreq_cpu_get(0), SLEEP_FREQ, 0);
> >  	if (ret < 0)
> >  		return NOTIFY_BAD;
> >  
> > -- 
> > 1.9.1
> 
> -- 
> viresh

--
Qiwu