V4L/DVB (13379): quickcam_messenger: possible buffer overflow while use strncat

In driver ./drivers/media/video/usbvideo/quickcam_messenger.c in line 91:

  91         usb_make_path(dev, cam->input_physname, sizeof(cam->input_physname));

After this line we use strncat:

  92         strncat(cam->input_physname, "/input0", sizeof(cam->input_physname));

where sizeof(cam->input_physname) returns length of cam->input_phisname
without length for null-symbol.  But this parameter must be - "maximum
numbers of bytes to copy", i.e.:
sizeof(cam->input_physname)-strlen(cam->input_physname)-1.

In this case, after call to usb_make_path the similar drivers use strlcat.

Like in: drivers/hid/usbhid/hid-core.c:
1152         usb_make_path(dev, hid->phys, sizeof(hid->phys));
1153         strlcat(hid->phys, "/input", sizeof(hid->phys));

Found by Linux Driver Verification Project.

Use strlcat instead of strncat.
Signed-off-by: NAlexander Strakh <strakh@ispras.ru>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NMauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/usbvideo/quickcam_messenger.c

@@ -89,7 +89,7 @@ static void qcm_register_input(struct qcm *cam, struct usb_device *dev)
 	int error;
 
 	usb_make_path(dev, cam->input_physname, sizeof(cam->input_physname));
-	strncat(cam->input_physname, "/input0", sizeof(cam->input_physname));
+	strlcat(cam->input_physname, "/input0", sizeof(cam->input_physname));
 
 	cam->input = input_dev = input_allocate_device();
 	if (!input_dev) {