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Commit 61e73cf5 authored by Kai Shen's avatar Kai Shen Committed by Greg Kroah-Hartman
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cpufreq: Add NULL checks to show() and store() methods of cpufreq 



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: default avatarKai Shen <shenkai8@huawei.com>
Reported-by: default avatarFeilong Lin <linfeilong@huawei.com>
Reviewed-by: default avatarFeilong Lin <linfeilong@huawei.com>
Acked-by: default avatarViresh Kumar <viresh.kumar@linaro.org>
[ rjw: Subject & changelog ]
Cc: All applicable <stable@vger.kernel.org>
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent f217cef9

drivers/cpufreq/cpufreq.c

+6 −0
Original line number Diff line number Diff line
@@ -909,6 +909,9 @@ 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);
@@ -923,6 +926,9 @@ 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().