CVE-2026-74549: hwmon: (nct6775-core) Prevent access to unsupported weight registers

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

hwmon: (nct6775-core) Prevent access to unsupported weight registers

Sashiko reports:

During initialization of the nct6116 chip, the driver sets data->pwmnum to 5. However, it assigns several NCT6106 register arrays (such as NCT6106REGWEIGHTDUTYSTEP, NCT6106REGWEIGHTTEMPSEL, and NCT6106REGWEIGHTTEMP) to data->REGPWM and data->REGWEIGHTTEMP. These arrays only contain 3 elements.

In nct6775updatepwm(), the driver iterates up to data->pwmnum. If data->haspwm has bits 3 or 4 set (which is structurally possible for nct6116), the loop attempts to read elements at index 3 and 4 from these 3-element arrays. This results in a global out-of-bounds read, which can be caught by KASAN.

Furthermore, the driver uses these garbage out-of-bounds values as hardware register addresses for subsequent read and write operations. This leads to invalid hardware register access, potentially causing hardware misconfiguration or system crashes.

The underlying problem is that the chip does support up to five fan control channels, but only the first three support weight control. Fix the problem by extending the affected weight register arrays with zeroed fields. The driver uses zeroed register addresses to determine if a register is supported or not, and skips accesses for unsupported registers.