backlight: catch invalid input

[Pavel Machek]

Currently, echo > brightness turns brightness to zero due to
insufficient checking. Add a test to catch that.

Signed-off-by: Pavel Machek <pavel@xxxxxxx>

diff --git a/drivers/video/backlight/backlight.c b/drivers/video/backlight/backlight.c
index fab0bc8..5c2e23d 100644
--- a/drivers/video/backlight/backlight.c
+++ b/drivers/video/backlight/backlight.c
@@ -86,6 +86,8 @@ static ssize_t backlight_store_power(str
 	int power = simple_strtoul(buf, &endp, 0);
 	size_t size = endp - buf;
 
+	if (!size)
+		return -EINVAL;
 	if (*endp && isspace(*endp))
 		size++;
 	if (size != count)


-- 
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