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Alexey Simakov ea62d22f57 hwmon: (tmp401) fix overflow caused by default conversion rate value 
[ Upstream commit 82f2aab35a ]

The driver computes conversion intervals using the formula:

    interval = (1 << (7 - rate)) * 125ms

where 'rate' is the sensor's conversion rate register value. According to
the datasheet, the power-on reset value of this register is 0x8, which
could be assigned to the register, after handling i2c general call.
Using this default value causes a result greater than the bit width of
left operand and an undefined behaviour in the calculation above, since
shifting by values larger than the bit width is undefined behaviour as
per C language standard.

Limit the maximum usable 'rate' value to 7 to prevent undefined
behaviour in calculations.

Found by Linux Verification Center (linuxtesting.org) with Svace.

Note (groeck):
    This does not matter in practice unless someone overwrites the chip
    configuration from outside the driver while the driver is loaded.
    The conversion time register is initialized with a value of 5 (500ms)
    when the driver is loaded, and the driver never writes a bad value.

Fixes: ca53e7640d ("hwmon: (tmp401) Convert to _info API")
Signed-off-by: Alexey Simakov <bigalex934@gmail.com>
Link: https://lore.kernel.org/r/20251211164342.6291-1-bigalex934@gmail.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2026-01-02 12:56:51 +01:00
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README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.