[PATCH 1/4] can: etas_es58x: populate ndo_change_mtu() to prevent buffer overflow

[Vincent Mailhol <mailhol@kernel.org>]

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 etas_es58x 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, es58x_start_xmit() receives a CAN XL frame which it is not
able to correctly handle and will thus misinterpret it as a CAN(FD)
frame.

This can result in a buffer overflow. For example, using the es581.4
variant, the frame will be dispatched to es581_4_tx_can_msg(), go
through the last check at the beginning of this function:

	if (can_is_canfd_skb(skb))
		return -EMSGSIZE;

and reach this line:

	memcpy(tx_can_msg->data, cf->data, 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!

Populate net_device_ops->ndo_change_mtu() to ensure that the
interface's MTU can not be set to anything bigger than CAN_MTU or
CANFD_MTU (depending on the device capabilities). By fixing the root
cause, this prevents the buffer overflow.

Fixes: 8537257874e9 ("can: etas_es58x: add core support for ETAS ES58X CAN USB interfaces")
Signed-off-by: Vincent Mailhol <mailhol@kernel.org>
---
 drivers/net/can/usb/etas_es58x/es58x_core.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/can/usb/etas_es58x/es58x_core.c b/drivers/net/can/usb/etas_es58x/es58x_core.c
index db1acf6d504cf37cec724d392c9f7fee2d1f6045..adc91873c083f968ff7571a5b0db5747988482c5 100644
--- a/drivers/net/can/usb/etas_es58x/es58x_core.c
+++ b/drivers/net/can/usb/etas_es58x/es58x_core.c
@@ -7,7 +7,7 @@
  *
  * Copyright (c) 2019 Robert Bosch Engineering and Business Solutions. All rights reserved.
  * Copyright (c) 2020 ETAS K.K.. All rights reserved.
- * Copyright (c) 2020-2022 Vincent Mailhol <mailhol.vincent@wanadoo.fr>
+ * Copyright (c) 2020-2025 Vincent Mailhol <mailhol@kernel.org>
  */
 
 #include <linux/unaligned.h>
@@ -1977,6 +1977,7 @@ static const struct net_device_ops es58x_netdev_ops = {
 	.ndo_stop = es58x_stop,
 	.ndo_start_xmit = es58x_start_xmit,
 	.ndo_eth_ioctl = can_eth_ioctl_hwts,
+	.ndo_change_mtu = can_change_mtu,
 };
 
 static const struct ethtool_ops es58x_ethtool_ops = {

-- 
2.49.1