CVE-2026-89941: iio: buffer: Make IIO DMA fence release RCU-safe

CVE-2026-89941: iio: buffer: Make IIO DMA fence release RCU-safe

[Greg Kroah-Hartman]

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

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

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

iio: buffer: Make IIO DMA fence release RCU-safe

The `dma_fence` documentation states that if a custom release
implementation is provided, the `dma_fence` object must be freed in an
RCU-safe way. The current `iio_dma_fence` implementation uses `kfree()`,
which might result in a use-after-free.

Remove the custom `release` implementation. This makes the DMA fence core
fall back to `dma_fence_free()`, which calls `kfree_rcu()` on the fence.
This requires that the fence be the first member of `struct iio_dma_fence`.

Using the default release method for extended DMA fence structures is a
common pattern.

The Linux kernel CVE team has assigned CVE-2026-89941 to this issue.


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

	Issue introduced in 6.11 with commit 3e26d9f08fbe0b73e951a5e810fdb7a332b7e37f and fixed in 6.12.110 with commit 311595dc0b5621f74d8eb4dc38ef4efcdfe7e769
	Issue introduced in 6.11 with commit 3e26d9f08fbe0b73e951a5e810fdb7a332b7e37f and fixed in 6.18.51 with commit 06a9460b8b792e109cbc934a856d02e5cff217ef
	Issue introduced in 6.11 with commit 3e26d9f08fbe0b73e951a5e810fdb7a332b7e37f and fixed in 7.2.5 with commit 11cef99491117d4264603df159c4ff5f3845a059
	Issue introduced in 6.11 with commit 3e26d9f08fbe0b73e951a5e810fdb7a332b7e37f and fixed in 7.3-rc1 with commit 8662e56c31cf23b61ca3d11b516efb94c35b8026

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-2026-89941
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/iio/industrialio-buffer.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/311595dc0b5621f74d8eb4dc38ef4efcdfe7e769
	https://git.kernel.org/stable/c/06a9460b8b792e109cbc934a856d02e5cff217ef
	https://git.kernel.org/stable/c/11cef99491117d4264603df159c4ff5f3845a059
	https://git.kernel.org/stable/c/8662e56c31cf23b61ca3d11b516efb94c35b8026