[ACPI] Fix Null pointer deref in video/lcd/brightness

http://bugzilla.kernel.org/show_bug.cgi?id=5571

Signed-off-by: Thomas Renninger <trenn@suse.de>
Signed-off-by: Nishanth Aravamudan <nacc@us.ibm.com>
Signed-off-by: Yu Luming <luming.yu@gmail.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Len Brown <len.brown@intel.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/drivers/acpi/video.c b/drivers/acpi/video.c
index f051b151580d..d10668f14699 100644
--- a/drivers/acpi/video.c
+++ b/drivers/acpi/video.c
@@ -812,7 +812,7 @@ acpi_video_device_write_brightness(struct file *file,
 
         ACPI_FUNCTION_TRACE("acpi_video_device_write_brightness");
 
-        if (!dev || count + 1 > sizeof str)
+        if (!dev || !dev->brightness || count + 1 > sizeof str)
                 return_VALUE(-EINVAL);
 
         if (copy_from_user(str, buffer, count))