From: Kai Shen <shenkai8@xxxxxxxxxx> 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@xxxxxxxxxx> Reported-by: Feilong Lin <linfeilong@xxxxxxxxxx> Reviewed-by: Feilong Lin <linfeilong@xxxxxxxxxx> Acked-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx> [ rjw: Subject & changelog ] Cc: All applicable <stable@xxxxxxxxxxxxxxx> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- 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().
