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cpufreq: Add NULL checks to show() and store() methods of cpufreq 

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>
This commit is contained in:
Kai Shen 2019-11-07 05:08:17 +00:00 committed by Rafael J. Wysocki
parent 8d2eecead5
commit e6e8df0726
1 changed files with 6 additions and 0 deletions
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6
drivers/cpufreq/cpufreq.c
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@ -933,6 +933,9 @@ static ssize_t show(struct kobject *kobj, struct attribute *attr, char *buf)
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);
@ -947,6 +950,9 @@ static ssize_t store(struct kobject *kobj, struct attribute *attr,
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().