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 ac1c7656fa717f29fac3ea073af63f0b9919ec9a ]
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 sun4i_can 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, hi3110_hard_start_xmit() receives a CAN XL frame which it is not able to correctly handle and will thus misinterpret it as a CAN frame. The driver will consume frame->len as-is with no further checks.
This can result in a buffer overflow later on in hi3110_hw_tx() on this line:
memcpy(buf + HI3110_FIFO_EXT_DATA_OFF, frame->data, frame->len);
Here, frame->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: 57e83fb9b746 ("can: hi311x: Add Holt HI-311x CAN driver") Signed-off-by: Vincent Mailhol mailhol@kernel.org Link: https://patch.msgid.link/20250918-can-fix-mtu-v1-2-0d1cada9393b@kernel.org Signed-off-by: Marc Kleine-Budde mkl@pengutronix.de Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/net/can/spi/hi311x.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/drivers/net/can/spi/hi311x.c b/drivers/net/can/spi/hi311x.c index 28273e84171a2..a7d594a5ad36f 100644 --- a/drivers/net/can/spi/hi311x.c +++ b/drivers/net/can/spi/hi311x.c @@ -807,6 +807,7 @@ static const struct net_device_ops hi3110_netdev_ops = { .ndo_open = hi3110_open, .ndo_stop = hi3110_stop, .ndo_start_xmit = hi3110_hard_start_xmit, + .ndo_change_mtu = can_change_mtu, };
static const struct of_device_id hi3110_of_match[] = {