CVE-2025-39987

Summary

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).

2. 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.

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/f2c247e9581024d8b3dd44cbe086bf2bebbef42c
• https://git.kernel.org/stable/c/8f351db6b2367991f0736b2cff082f5de4872113
• https://git.kernel.org/stable/c/7ab85762274c0fa997f0ef9a2307b2001aae43c4
• https://git.kernel.org/stable/c/57d332ce8c921d0e340650470bb0c1d707f216ee
• https://git.kernel.org/stable/c/be1b25005fd0f9d4e78bec6695711ef87ee33398
• https://git.kernel.org/stable/c/def814b4ba31b563584061d6895d5ff447d5bc14
• https://git.kernel.org/stable/c/e77fdf9e33a83a08f04ab0cb68c19ddb365a622f
• https://git.kernel.org/stable/c/ac1c7656fa717f29fac3ea073af63f0b9919ec9a

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