From: Kai Shen shenkai8@huawei.com
commit e6e8df07268c1f75dd9215536e2ce4587b70f977 upstream.
Add NULL checks to show() and store() in cpufreq.c to avoid attempts to invoke a NULL callback.
Though some interfaces of cpufreq are set as read-only, users can still get write permission using chmod which can lead to a kernel crash, as follows:
chmod +w /sys/devices/system/cpu/cpu0/cpufreq/scaling_cur_freq echo 1 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_cur_freq
This bug was found in linux 4.19.
Signed-off-by: Kai Shen shenkai8@huawei.com Reported-by: Feilong Lin linfeilong@huawei.com Reviewed-by: Feilong Lin linfeilong@huawei.com Acked-by: Viresh Kumar viresh.kumar@linaro.org [ rjw: Subject & changelog ] Cc: All applicable stable@vger.kernel.org Signed-off-by: Rafael J. Wysocki rafael.j.wysocki@intel.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/cpufreq/cpufreq.c | 6 ++++++ 1 file changed, 6 insertions(+)
--- a/drivers/cpufreq/cpufreq.c +++ b/drivers/cpufreq/cpufreq.c @@ -909,6 +909,9 @@ static ssize_t show(struct kobject *kobj struct freq_attr *fattr = to_attr(attr); ssize_t ret;
+ if (!fattr->show) + return -EIO; + down_read(&policy->rwsem); ret = fattr->show(policy, buf); up_read(&policy->rwsem); @@ -923,6 +926,9 @@ static ssize_t store(struct kobject *kob struct freq_attr *fattr = to_attr(attr); ssize_t ret = -EINVAL;
+ if (!fattr->store) + return -EIO; + /* * cpus_read_trylock() is used here to work around a circular lock * dependency problem with respect to the cpufreq_register_driver().