[PATCH] can: dev: can_dropped_invalid_skb: drop CAN XL frames on non-CAN XL devices

Sending a PF_PACKET bypasses the CAN framework logic and can directly
reach a CAN driver's xmit() function. The PF_PACKET framework only
checks that skb->len does not exceed the net_device MTU.

For a CAN device that is not CAN XL capable, anything above CANFD_MTU
(72 bytes) is therefore dropped before it reaches the driver. However,
CAN XL frames are variable length. can_is_canxl_skb() accepts lengths in
the range CANXL_HDR_SIZE + CANXL_MIN_DLEN up to CANXL_MTU, i.e. 13 to
2060 bytes.

As a result, an ETH_P_CANXL skb with a length between 13 and 72 bytes
can pass both the MTU and the can_dropped_invalid_skb() checks.

A driver that does not support CAN XL will interpret canxl_frame->flags
as a length because of the overlap with can_frame->len. And because
CANXL_XLF is set, the resulting length is between 128 and 255. For
drivers that do not check can_frame->len before copying can_frame->data,
as most drivers do, this results in a buffer overflow of up to 247
bytes.

Drop ETH_P_CANXL skbs if the device does not have the CAN_CAP_XL
capability. Keep can_is_canxl_skb() for the validation of CAN XL skbs.

Closes: https://sashiko.dev/#/patchset/[email protected]?part=1
Fixes: fb08cba12b52 ("can: canxl: update CAN infrastructure for CAN XL frames")
Signed-off-by: Vincent Mailhol <[email protected]>
---
Cc: [email protected]
---
 drivers/net/can/dev/skb.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/can/dev/skb.c b/drivers/net/can/dev/skb.c
index 95fcdc1026f8..4f7a189de265 100644
--- a/drivers/net/can/dev/skb.c
+++ b/drivers/net/can/dev/skb.c
@@ -4,6 +4,7 @@
  * Copyright (C) 2008-2009 Wolfgang Grandegger <[email protected]>
  */
 
+#include <linux/can/can-ml.h>
 #include <linux/can/dev.h>
 #include <linux/module.h>
 #include <net/can.h>
@@ -384,7 +385,7 @@ bool can_dropped_invalid_skb(struct net_device *dev, struct sk_buff *skb)
 		break;
 
 	case ETH_P_CANXL:
-		if (!can_is_canxl_skb(skb))
+		if (!can_cap_enabled(dev, CAN_CAP_XL) || !can_is_canxl_skb(skb))
 			goto inval_skb;
 		break;
 

---
base-commit: 8ba098e6b6ff0db8edf28528d1552be261af30d4
change-id: 20260731-drop_canxl_frames-189872010abc

Best regards,
--  
Vincent Mailhol <[email protected]>