5.4-stable review patch. If anyone has any objections, please let me know.
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From: Vincent Mailhol mailhol@kernel.org
[ Upstream commit 17c8d794527f01def0d1c8b7dc2d7b8d34fed0e6 ]
Sending an PF_PACKET allows to bypass the CAN framework logic and to directly reach the xmit() function of a CAN driver. The only check which is performed by the PF_PACKET framework is to make sure that skb->len fits the interface's MTU.
Unfortunately, because the mcba_usb driver does not populate its net_device_ops->ndo_change_mtu(), it is possible for an attacker to configure an invalid MTU by doing, for example:
$ ip link set can0 mtu 9999
After doing so, the attacker could open a PF_PACKET socket using the ETH_P_CANXL protocol:
socket(PF_PACKET, SOCK_RAW, htons(ETH_P_CANXL))
to inject a malicious CAN XL frames. For example:
struct canxl_frame frame = { .flags = 0xff, .len = 2048, };
The CAN drivers' xmit() function are calling can_dev_dropped_skb() to check that the skb is valid, unfortunately under above conditions, the malicious packet is able to go through can_dev_dropped_skb() checks:
1. the skb->protocol is set to ETH_P_CANXL which is valid (the function does not check the actual device capabilities).
2. the length is a valid CAN XL length.
And so, mcba_usb_start_xmit() receives a CAN XL frame which it is not able to correctly handle and will thus misinterpret it as a CAN frame.
This can result in a buffer overflow. The driver will consume cf->len as-is with no further checks on these lines:
usb_msg.dlc = cf->len;
memcpy(usb_msg.data, cf->data, usb_msg.dlc);
Here, cf->len corresponds to the flags field of the CAN XL frame. In our previous example, we set canxl_frame->flags to 0xff. Because the maximum expected length is 8, a buffer overflow of 247 bytes occurs!
Populate net_device_ops->ndo_change_mtu() to ensure that the interface's MTU can not be set to anything bigger than CAN_MTU. By fixing the root cause, this prevents the buffer overflow.
Fixes: 51f3baad7de9 ("can: mcba_usb: Add support for Microchip CAN BUS Analyzer") Signed-off-by: Vincent Mailhol mailhol@kernel.org Link: https://patch.msgid.link/20250918-can-fix-mtu-v1-4-0d1cada9393b@kernel.org Signed-off-by: Marc Kleine-Budde mkl@pengutronix.de Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/net/can/usb/mcba_usb.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/drivers/net/can/usb/mcba_usb.c b/drivers/net/can/usb/mcba_usb.c index 16fb4fc265183..e43bd02401a24 100644 --- a/drivers/net/can/usb/mcba_usb.c +++ b/drivers/net/can/usb/mcba_usb.c @@ -769,6 +769,7 @@ static const struct net_device_ops mcba_netdev_ops = { .ndo_open = mcba_usb_open, .ndo_stop = mcba_usb_close, .ndo_start_xmit = mcba_usb_start_xmit, + .ndo_change_mtu = can_change_mtu, };
/* Microchip CANBUS has hardcoded bittiming values by default.