The driver expects to receive a struct gs_host_frame in
gs_usb_receive_bulk_callback().

Use struct_group to describe the header of the struct gs_host_frame and
check that we have at least received the header before accessing any
members of it.

To resubmit the URB, do not dereference the pointer chain
"dev->parent->hf_size_rx" but use "parent->hf_size_rx" instead. Since
"urb->context" contains "parent", it is always defined, while "dev" is not
defined if the URB it too short.

Fixes: d08e973a77d1 ("can: gs_usb: Added support for the GS_USB CAN devices")
Link: https://patch.msgid.link/20251114-gs_usb-fix-usb-callbacks-v1-2-a29b42eacada@pengutronix.de
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
---
 drivers/net/can/usb/gs_usb.c | 26 +++++++++++++++++++-------
 1 file changed, 19 insertions(+), 7 deletions(-)

diff --git a/drivers/net/can/usb/gs_usb.c b/drivers/net/can/usb/gs_usb.c
index fa9bab8c89ae..51f8d694104d 100644
--- a/drivers/net/can/usb/gs_usb.c
+++ b/drivers/net/can/usb/gs_usb.c
@@ -262,13 +262,15 @@ struct canfd_quirk {
 } __packed;
 
 struct gs_host_frame {
-	u32 echo_id;
-	__le32 can_id;
+	struct_group(header,
+		u32 echo_id;
+		__le32 can_id;
 
-	u8 can_dlc;
-	u8 channel;
-	u8 flags;
-	u8 reserved;
+		u8 can_dlc;
+		u8 channel;
+		u8 flags;
+		u8 reserved;
+	);
 
 	union {
 		DECLARE_FLEX_ARRAY(struct classic_can, classic_can);
@@ -576,6 +578,7 @@ static void gs_usb_receive_bulk_callback(struct urb *urb)
 	int rc;
 	struct net_device_stats *stats;
 	struct gs_host_frame *hf = urb->transfer_buffer;
+	unsigned int minimum_length;
 	struct gs_tx_context *txc;
 	struct can_frame *cf;
 	struct canfd_frame *cfd;
@@ -594,6 +597,15 @@ static void gs_usb_receive_bulk_callback(struct urb *urb)
 		return;
 	}
 
+	minimum_length = sizeof(hf->header);
+	if (urb->actual_length < minimum_length) {
+		dev_err_ratelimited(&parent->udev->dev,
+				    "short read (actual_length=%u, minimum_length=%u)\n",
+				    urb->actual_length, minimum_length);
+
+		goto resubmit_urb;
+	}
+
 	/* device reports out of range channel id */
 	if (hf->channel >= parent->channel_cnt)
 		goto device_detach;
@@ -687,7 +699,7 @@ static void gs_usb_receive_bulk_callback(struct urb *urb)
 resubmit_urb:
 	usb_fill_bulk_urb(urb, parent->udev,
 			  parent->pipe_in,
-			  hf, dev->parent->hf_size_rx,
+			  hf, parent->hf_size_rx,
 			  gs_usb_receive_bulk_callback, parent);
 
 	rc = usb_submit_urb(urb, GFP_ATOMIC);
-- 
2.51.0