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SubjectRe: [PATCH] cpufreq: s3c: avoid use after free issue in xxx_cpufreq_reboot_notifier_evt()
On 28-12-19, 14:43, 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.

There is no UAF problem here, but that we do cpufreq_cpu_get() with a
corresponding cpufreq_cpu_put().

> Signed-off-by: chenqiwu <chenqiwu@xiaomi.com>
> ---
> 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 ?

> + 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

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