Time-of-Check to Time-of-Use Race Condition in Linux Kernel's Fan Control Functionality

CVE-2025-38217

What is CVE-2025-38217?

A vulnerability exists in the Linux kernel related to the hwmon subsystem, specifically within the fts_read() function where a Time-of-Check to Time-of-Use (TOCTOU) race condition occurs. This flaw arises when the code accesses the shared variable data->fan_source[channel] twice without synchronization, allowing a possible thread interleaving that can lead to unexpected behavior. If a concurrent thread alters the variable between the initial check and its subsequent use, a large value could be erroneously processed, causing crashes or incorrect data to be sent to userspace. The recent patch addresses this issue by consolidating the variable read into a local context, significantly improving the robustness of the code and preventing undefined behavior from occurring.

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