CVE-2025-39988

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

can: etases58x: populate ndochange_mtu() to prevent buffer overflow

Sending an PFPACKET 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 PFPACKET framework is to make sure that skb->len fits the interface's MTU.

Unfortunately, because the etases58x driver does not populate its netdeviceops->ndochange_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 PFPACKET socket using the ETHP_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 candevdroppedskb() to check that the skb is valid, unfortunately under above conditions, the malicious packet is able to go through candevdroppedskb() checks:

1. the skb->protocol is set to ETHPCANXL which is valid (the function does not check the actual device capabilities).

2. the length is a valid CAN XL length.

And so, es58xstartxmit() 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 es5814txcanmsg(), 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 netdeviceops->ndochangemtu() to ensure that the interface's MTU can not be set to anything bigger than CANMTU or CANFDMTU (depending on the device capabilities). By fixing the root cause, this prevents the buffer overflow.