Input: uinput - fix undefined behavior in uinput_validate_absinfo()

An integer overflow may arise in uinput_validate_absinfo() if "max - min"
can't be represented by an "int". We should check for overflow before
trying to use the result.
Reported-by: Kyungtae Kim <kt0755@gmail.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Cc: stable@vger.kernel.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/misc/uinput.c

@@ -39,6 +39,7 @@
 #include <linux/init.h>
 #include <linux/fs.h>
 #include <linux/miscdevice.h>
+#include <linux/overflow.h>
 #include <linux/input/mt.h>
 #include "../input-compat.h"
 
@@ -405,7 +406,7 @@ static int uinput_open(struct inode *inode, struct file *file)
 static int uinput_validate_absinfo(struct input_dev *dev, unsigned int code,
 				   const struct input_absinfo *abs)
 {
-	int min, max;
+	int min, max, range;
 
 	min = abs->minimum;
 	max = abs->maximum;
@@ -417,7 +418,7 @@ static int uinput_validate_absinfo(struct input_dev *dev, unsigned int code,
 		return -EINVAL;
 	}
 
-	if (abs->flat > max - min) {
+	if (!check_sub_overflow(max, min, &range) && abs->flat > range) {
 		printk(KERN_DEBUG
 		       "%s: abs_flat #%02x out of range: %d (min:%d/max:%d)\n",
 		       UINPUT_NAME, code, abs->flat, min, max);