PM / Sleep: Require CAP_BLOCK_SUSPEND to use wake_lock/wake_unlock

Require processes wanting to use the wake_lock/wake_unlock sysfs
files to have the CAP_BLOCK_SUSPEND capability, which also is
required for the eventpoll EPOLLWAKEUP flag to be effective, so that
all interfaces related to blocking autosleep depend on the same
capability.
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Cc: stable@vger.kernel.org
Acked-by: Michael Kerrisk <mtk.man-pages@gmail.com>

kernel/power/wakelock.c

@@ -9,6 +9,7 @@
  * manipulate wakelocks on Android.
  */
 
+#include <linux/capability.h>
 #include <linux/ctype.h>
 #include <linux/device.h>
 #include <linux/err.h>
@@ -188,6 +189,9 @@ int pm_wake_lock(const char *buf)
 	size_t len;
 	int ret = 0;
 
+	if (!capable(CAP_BLOCK_SUSPEND))
+		return -EPERM;
+
 	while (*str && !isspace(*str))
 		str++;
 
@@ -231,6 +235,9 @@ int pm_wake_unlock(const char *buf)
 	size_t len;
 	int ret = 0;
 
+	if (!capable(CAP_BLOCK_SUSPEND))
+		return -EPERM;
+
 	len = strlen(buf);
 	if (!len)
 		return -EINVAL;