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commit 6f71507415841d1a6d38118e5fa0eaf0caab9c17 upstream.
The scale() functions detects invalid parameters, but continues
its calculations anyway. This causes bad results if negative values
are used for unsigned operations. Worst case, a division by 0 error
will be seen if source_min == source_max.
On top of that, after v6.13, the sequence of WARN_ON() followed by clamp()
may result in a build error with gcc 13.x.
drivers/gpu/drm/i915/display/intel_backlight.c: In function 'scale':
include/linux/compiler_types.h:542:45: error:
call to '__compiletime_assert_415' declared with attribute error:
clamp() low limit source_min greater than high limit source_max
This happens if the compiler decides to rearrange the code as follows.
if (source_min > source_max) {
WARN(..);
/* Do the clamp() knowing that source_min > source_max */
source_val = clamp(source_val, source_min, source_max);
} else {
/* Do the clamp knowing that source_min <= source_max */
source_val = clamp(source_val, source_min, source_max);
}
Fix the problem by evaluating the return values from WARN_ON and returning
immediately after a warning. While at it, fix divide by zero error seen
if source_min == source_max.
Analyzed-by: Linus Torvalds <torvalds@linux-foundation.org>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Suggested-by: David Laight <david.laight.linux@gmail.com>
Cc: David Laight <david.laight.linux@gmail.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250121145203.2851237-1-linux@roeck-us.net
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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 Restructured Text 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.