CVE-2026-72482: gpib: fix double decrement of descriptor_busy in command_ioctl()

CVE-2026-72482: gpib: fix double decrement of descriptor_busy in command_ioctl()

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

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

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

gpib: fix double decrement of descriptor_busy in command_ioctl()

commit d1857f8296dc ("gpib: fix use-after-free in IO ioctl handlers")
introduced a descriptor_busy reference counter to pin struct
gpib_descriptor across IO ioctl operations.  In command_ioctl(), the
error path inside the loop decrements descriptor_busy and breaks, but
execution then falls through to the unconditional decrement after the
loop, underflowing the counter to -1.

This re-enables the use-after-free that the original fix was meant to
prevent: a concurrent close_dev_ioctl() sees descriptor_busy == 0 on
an actively-used descriptor and frees it.

Remove the early decrement from the error path.  The post-loop
decrement already handles all exit paths, matching the correct pattern
used in read_ioctl() and write_ioctl().

The Linux kernel CVE team has assigned CVE-2026-72482 to this issue.


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

	Issue introduced in 6.18.22 with commit cae26eff1b56d78bed7873cf3e60a2b1bdd4da6c and fixed in 6.18.40 with commit fdee9f207a48ce204ec6cfceaa1459d2473600a5
	Issue introduced in 7.0 with commit d1857f8296dceb75d00ab857fc3c61bc00c7f5c6 and fixed in 7.1.5 with commit 8b5f1d295dda8677e4545ce340053fcfa8b634c7
	Issue introduced in 7.0 with commit d1857f8296dceb75d00ab857fc3c61bc00c7f5c6 and fixed in 7.2-rc1 with commit c4faab452b3c1ada003d49c477609dd80523b9bf
	Issue introduced in 6.19.12 with commit 28c75dd143ead62e0dfac564c79d251e21d5d74b

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-2026-72482
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/gpib/common/gpib_os.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/fdee9f207a48ce204ec6cfceaa1459d2473600a5
	https://git.kernel.org/stable/c/8b5f1d295dda8677e4545ce340053fcfa8b634c7
	https://git.kernel.org/stable/c/c4faab452b3c1ada003d49c477609dd80523b9bf