Description

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

hwmon: (ftsteutates) Fix TOCTOU race in fts_read()

In the fts_read() function, when handling hwmon_pwm_auto_channels_temp,
the code accesses the shared variable data->fan_source[channel] twice
without holding any locks. It is first checked against
FTS_FAN_SOURCE_INVALID, and if the check passes, it is read again
when used as an argument to the BIT() macro.

This creates a Time-of-Check to Time-of-Use (TOCTOU) race condition.
Another thread executing fts_update_device() can modify the value of
data->fan_source[channel] between the check and its use. If the value
is changed to FTS_FAN_SOURCE_INVALID (0xff) during this window, the
BIT() macro will be called with a large shift value (BIT(255)).
A bit shift by a value greater than or equal to the type width is
undefined behavior and can lead to a crash or incorrect values being
returned to userspace.

Fix this by reading data->fan_source[channel] into a local variable
once, eliminating the race condition. Additionally, add a bounds check
to ensure the value is less than BITS_PER_LONG before passing it to
the BIT() macro, making the code more robust against undefined behavior.

This possible bug was found by an experimental static analysis tool
developed by our team.

Classification

CVE ID: CVE-2025-38217

Affected Products

Vendor: Linux

Product: Linux

Exploit Prediction Scoring System (EPSS)

EPSS Score: 0.02% (probability of being exploited)

EPSS Percentile: 4.54% (scored less or equal to compared to others)

EPSS Date: 2025-07-10 (when was this score calculated)

References

https://nvd.nist.gov/vuln/detail/CVE-2025-38217
https://git.kernel.org/stable/c/d95d87841d2a575bed3691884e8fedef57d7710d
https://git.kernel.org/stable/c/83e2ba8971ccd8fc08319fc7593288f070d80a76
https://git.kernel.org/stable/c/4d646f627d3b7ed1cacca66e598af8bcd632d465
https://git.kernel.org/stable/c/14c9ede9ca4cd078ad76a6ab9617b81074eb58bf

Timeline