CVE-2025-39985 — can: mcba_usb: populate ndo_change_mtu() to prevent buffer overflow

Affected: Linux

In the Linux kernel, the following vulnerability has been resolved:

can: mcba_usb: populate ndo_change_mtu() to prevent buffer overflow

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.…

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CVE-2025-39985 — can: mcba_usb: populate ndo_change_mtu() to prevent buffer overflow