CVE-2026-64238: gpio: shared: fix deadlock on shared proxy's parent removal

From: Greg Kroah-Hartman <[email protected]>

Description
===========

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

gpio: shared: fix deadlock on shared proxy's parent removal

Commit 710abda58055 ("gpio: shared: call gpio_chip::of_xlate() if set")
used the mutex embedded in struct gpio_shared_entry to protect the
offset field which now can be modified after assignment. The critical
section however is too wide and introduced a potential deadlock on the
removal of the shared GPIO proxy's parent.

Make the critical section shorter - only protect the offset when it's
being read.

While at it: mention the fact that the entry lock is now also used to
protect against concurrent access to the offset field in the structure's
documentation.

The Linux kernel CVE team has assigned CVE-2026-64238 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 7.0 with commit 710abda58055ed5eaa8958107633cc12a365c328 and fixed in 7.0.12 with commit a554dfcd30dd5e41d1d67387b3bb85cea83e12e1
	Issue introduced in 7.0 with commit 710abda58055ed5eaa8958107633cc12a365c328 and fixed in 7.1 with commit a1b836607304f71051f9f9dcccf8b5097b86a1fb
	Issue introduced in 6.19.12 with commit 28f488e7b327630686378bb1d24e22cfc3fc162d

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-64238
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	drivers/gpio/gpiolib-shared.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/a554dfcd30dd5e41d1d67387b3bb85cea83e12e1
	https://git.kernel.org/stable/c/a1b836607304f71051f9f9dcccf8b5097b86a1fb