[PATCH 6.18 139/314] can: ucan: Fix infinite loop from zero-length messages

Sasha Levin
2026-03-10T11:26:52Z

From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

commit 1e446fd0582ad8be9f6dafb115fc2e7245f9bea7 upstream.

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@pengutronix.de>
Cc: Vincent Mailhol <mailhol@kernel.org>
Cc: stable@kernel.org
Assisted-by: gkh_clanker_2000
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://patch.msgid.link/2026022319-huff-absurd-6a18@gregkh
Fixes: 9f2d3eae88d2 ("can: ucan: add driver for Theobroma Systems UCAN devices")
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
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 07406daf7c88e..6c90b4a7d955a 100644
--- a/drivers/net/can/usb/ucan.c
+++ b/drivers/net/can/usb/ucan.c
@@ -749,7 +749,7 @@ 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);
--
2.51.0