Linux Kernel CVE-2025-39987

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

can: hi311x: 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 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).

1. 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.

The vulnerability affects the Linux kernel's hi311x CAN driver (Holt HI-3110 SPI CAN controller) across multiple maintained kernel branches prior to the fix; exact version boundaries are not provided as CPE data in the input, and affected ranges must be derived from the stable-tree backport commits. Fixes are distributed as git.kernel.org stable commits (e.g., 57d332ce8c92, 7ab85762274c, 8f351db6b236, ac1c7656fa71, be1b25005fd0, def814b4ba31, e77fdf9e33a8, f2c247e95810), indicating the patch was applied to mainline and backported to several stable series. Any distribution kernel that ships the hi311x driver and predates these commits should be considered affected until the vendor confirms a patched build.