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Uwe Kleine-König 4230e8cd2f pwm: Ensure ioctl() returns a negative errno on error 
[ Upstream commit c198b7773c ]

copy_to_user() returns the number of bytes not copied, thus if there is
a problem a positive number. However the ioctl callback is supposed to
return a negative error code on error.

This error is a unfortunate as strictly speaking it became ABI with the
introduction of pwm character devices. However I never saw the issue in
real life -- I found this by code inspection -- and it only affects an
error case where readonly memory is passed to the ioctls or the address
mapping changes while the ioctl is active. Also there are already error
cases returning negative values, so the calling code must be prepared to
see such values already.

Fixes: 9c06f26ba5 ("pwm: Add support for pwmchip devices for faster and easier userspace access")
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Link: https://patch.msgid.link/20260119151325.571857-2-u.kleine-koenig@baylibre.com
Signed-off-by: Uwe Kleine-König <ukleinek@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2026-01-30 10:32:12 +01:00
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README

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.