CVE-2025-22003

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

can: ucan: fix out of bound read in strscpy() source

Commit 7fdaf8966aae (can: ucan: use strscpy() to instead of strncpy()) unintentionally introduced a one byte out of bound read on strscpy()s source argument (which is kind of ironic knowing that strscpy() is meant to be a more secure alternative :)).

Lets consider below buffers:

dest[len + 1]; /* will be NUL terminated / src[len]; / may not be NUL terminated */

When doing:

strncpy(dest, src, len); dest[len] = 0;

strncpy() will read up to len bytes from src.

On the other hand:

strscpy(dest, src, len + 1);

will read up to len + 1 bytes from src, that is to say, an out of bound read of one byte will occur on src if it is not NUL terminated. Note that the src[len] byte is never copied, but strscpy() still needs to read it to check whether a truncation occurred or not.

This exact pattern happened in ucan.

The root cause is that the source is not NUL terminated. Instead of doing a copy in a local buffer, directly NUL terminate it as soon as usb_control_msg() returns. With this, the local firmware_str[] variable can be removed.

On top of this do a couple refactors:

• ucan_ctl_payload->raw is only used for the firmware string, so rename it to ucan_ctl_payload->fw_str and change its type from u8 to char.

• ucan_device_request_in() is only used to retrieve the firmware string, so rename it to ucan_get_fw_str() and refactor it to make it directly handle all the string termination logic.

Affected Software

References

• https://git.kernel.org/stable/c/1d22a122ffb116c3cf78053e812b8b21f8852ee9
• https://git.kernel.org/stable/c/8cec9e314d3360fc1d8346297c41a6ee45cb45a9
• https://git.kernel.org/stable/c/a4994161a61bc8fd71d105c579d847cefee99262
• https://git.kernel.org/stable/c/cc29775a8a72d7f3b56cc026796ad99bd65804a7