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 61da0bd4102c459823fbe6b8b43b01fb6ace4a22 ]
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, sun4ican_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 this line:
dlc = cf->len;
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 a couple line below when doing:
for (i = 0; i < dlc; i++) writel(cf->data[i], priv->base + (dreg + i * 4));
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: 0738eff14d81 ("can: Allwinner A10/A20 CAN Controller support - Kernel module") Signed-off-by: Vincent Mailhol mailhol@kernel.org Link: https://patch.msgid.link/20250918-can-fix-mtu-v1-3-0d1cada9393b@kernel.org Signed-off-by: Marc Kleine-Budde mkl@pengutronix.de Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/net/can/sun4i_can.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/drivers/net/can/sun4i_can.c b/drivers/net/can/sun4i_can.c index 0eddd5779e5a2..a1e151d373597 100644 --- a/drivers/net/can/sun4i_can.c +++ b/drivers/net/can/sun4i_can.c @@ -752,6 +752,7 @@ static const struct net_device_ops sun4ican_netdev_ops = { .ndo_open = sun4ican_open, .ndo_stop = sun4ican_close, .ndo_start_xmit = sun4ican_start_xmit, + .ndo_change_mtu = can_change_mtu, };
static const struct of_device_id sun4ican_of_match[] = {