From: Seungjin Bae <eeodqql09@gmail.com>

The `kvaser_usb_leaf_read_bulk_callback()` function parse received
command buffers from the device. The firmware may insert zero-length
placeholder commands to handle alignment with the USB endpoint's
wMaxPacketSize.

The driver attempts to skip these placeholders by aligning the buffer
position `pos` to the next packet boundary using `round_up()` function.

However, if zero-length command is found exactly on a packet boundary
(i.e., `pos` is a multiple of wMaxPacketSize, including 0), `round_up`
function will return the unchanged value of `pos`. This prevents `pos`
to be increased, causing an infinite loop in the parsing logic.

I fixed this in the function by using `pos + 1` instead. This ensures
that even if `pos` is on a boundary, the calculation is based on
`pos + 1`, forcing `round_up()` to always return the next aligned
boundary.

Fixes: 7259124eac7d ("can: kvaser_usb: Split driver into kvaser_usb_core.c and kvaser_usb_leaf.c")
Signed-off-by: Seungjin Bae <eeodqql09@gmail.com>
---
 drivers/net/can/usb/kvaser_usb/kvaser_usb_leaf.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/can/usb/kvaser_usb/kvaser_usb_leaf.c b/drivers/net/can/usb/kvaser_usb/kvaser_usb_leaf.c
index c29828a94ad0..4da6d4ba4e1e 100644
--- a/drivers/net/can/usb/kvaser_usb/kvaser_usb_leaf.c
+++ b/drivers/net/can/usb/kvaser_usb/kvaser_usb_leaf.c
@@ -1732,7 +1732,7 @@ static void kvaser_usb_leaf_read_bulk_callback(struct kvaser_usb *dev,
 		 * number of events in case of a heavy rx load on the bus.
 		 */
 		if (cmd->len == 0) {
-			pos = round_up(pos, le16_to_cpu
+			pos = round_up(pos + 1, le16_to_cpu
 						(dev->bulk_in->wMaxPacketSize));
 			continue;
 		}
-- 
2.43.0

On 22.10.2025 20:39:09, pip-izony wrote:
> From: Seungjin Bae <eeodqql09@gmail.com>
> 
> The `kvaser_usb_leaf_read_bulk_callback()` function parse received
> command buffers from the device. The firmware may insert zero-length
> placeholder commands to handle alignment with the USB endpoint's
> wMaxPacketSize.
> 
> The driver attempts to skip these placeholders by aligning the buffer
> position `pos` to the next packet boundary using `round_up()`
> function.

What about the round_up() in kvaser_usb_leaf_wait_cmd()? Is it also
affected by this problem?

Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde          |
Embedded Linux                   | https://www.pengutronix.de |
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From: Seungjin Bae <eeodqql09@gmail.com>

`kvaser_usb_leaf_wait_cmd()` and `kvaser_usb_leaf_read_bulk_callback`
functions contain logic to handle zero-length commands. These commands
are used to align data to the USB endpoint's wMaxPacketSize boundary.

The driver attempts to skip these placeholders by aligning the buffer
position `pos` to the next packet boundary using `round_up()` function.

However, if zero-length command is found exactly on a packet boundary
(i.e., `pos` is a multiple of wMaxPacketSize, including 0), `round_up`
function will return the unchanged value of `pos`. This prevents `pos`
to be increased, causing an infinite loop in the parsing logic.

This patch fixes this in the function by using `pos + 1` instead.
This ensures that even if `pos` is on a boundary, the calculation is
based on `pos + 1`, forcing `round_up()` to always return the next
aligned boundary.

Fixes: 7259124eac7d ("can: kvaser_usb: Split driver into kvaser_usb_core.c and kvaser_usb_leaf.c")
Signed-off-by: Seungjin Bae <eeodqql09@gmail.com>
---
 v1 -> v2: Apply the same infinite loop fix to kvaser_usb_leaf_wait_cmd()
 
 drivers/net/can/usb/kvaser_usb/kvaser_usb_leaf.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/can/usb/kvaser_usb/kvaser_usb_leaf.c b/drivers/net/can/usb/kvaser_usb/kvaser_usb_leaf.c
index c29828a94ad0..1167d38344f1 100644
--- a/drivers/net/can/usb/kvaser_usb/kvaser_usb_leaf.c
+++ b/drivers/net/can/usb/kvaser_usb/kvaser_usb_leaf.c
@@ -685,7 +685,7 @@ static int kvaser_usb_leaf_wait_cmd(const struct kvaser_usb *dev, u8 id,
 			 * for further details.
 			 */
 			if (tmp->len == 0) {
-				pos = round_up(pos,
+				pos = round_up(pos + 1,
 					       le16_to_cpu
 						(dev->bulk_in->wMaxPacketSize));
 				continue;
@@ -1732,7 +1732,7 @@ static void kvaser_usb_leaf_read_bulk_callback(struct kvaser_usb *dev,
 		 * number of events in case of a heavy rx load on the bus.
 		 */
 		if (cmd->len == 0) {
-			pos = round_up(pos, le16_to_cpu
+			pos = round_up(pos + 1, le16_to_cpu
 						(dev->bulk_in->wMaxPacketSize));
 			continue;
 		}
-- 
2.43.0