[PATCH] can: ucan: Fix infinite loop from zero-length messages

[Greg Kroah-Hartman]

If a broken ucan device gets a message with the message length field set
to 0, then the driver will loop for forever in
ucan_read_bulk_callback(), hanging the system.  If the length is 0, just
skip the message and go on to the next one.

This has been fixed in the kvaser_usb driver in the past in commit
0c73772cd2b8 ("can: kvaser_usb: leaf: Fix potential infinite loop in
command parsers"), so there must be some broken devices out there like
this somewhere.

Cc: Marc Kleine-Budde <mkl@xxxxxxxxxxxxxx>
Cc: Vincent Mailhol <mailhol@xxxxxxxxxx>
Cc: stable <stable@xxxxxxxxxx>
Assisted-by: gkh_clanker_2000
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/net/can/usb/ucan.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/can/usb/ucan.c b/drivers/net/can/usb/ucan.c
index c79508b1c43e..0ea0ac75e42f 100644
--- a/drivers/net/can/usb/ucan.c
+++ b/drivers/net/can/usb/ucan.c
@@ -748,7 +748,7 @@ static void ucan_read_bulk_callback(struct urb *urb)
 		len = le16_to_cpu(m->len);
 
 		/* check sanity (length of content) */
-		if (urb->actual_length - pos < len) {
+		if ((len == 0) || (urb->actual_length - pos < len)) {
 			netdev_warn(up->netdev,
 				    "invalid message (short; no data; l:%d)\n",
 				    urb->actual_length);
-- 
2.53.0