CVE-2025-38556

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

HID: core: Harden s32ton() against conversion to 0 bits

Testing by the syzbot fuzzer showed that the HID core gets a shift-out-of-bounds exception when it tries to convert a 32-bit quantity to a 0-bit quantity. Ideally this should never occur, but there are buggy devices and some might have a report field with size set to zero; we shouldn't reject the report or the device just because of that.

Instead, harden the s32ton() routine so that it returns a reasonable result instead of crashing when it is called with the number of bits set to 0 -- the same as what snto32() does.

HID core could crash on malformed devices that define a 0-bit report field, causing a shift-out-of-bounds in s32ton(). Exploitation requires only connecting a malicious HID device (no privileges or user interaction), leading to kernel crash.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.