CVE-2026-89764: rust: devres: fix race between concurrent revokers

CVE-2026-89764: rust: devres: fix race between concurrent revokers

[Greg Kroah-Hartman]

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

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

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

rust: devres: fix race between concurrent revokers

There is a potential race condition when two paths try to revoke a
Devres concurrently.

The driver core's devres_release_all() calls Revocable::revoke() via the
release callback, while Devres::drop() calls revoke_nosync() on another
CPU.

The revoker that does not claim the is_available swap returns
immediately, but the revoker that did may still be executing
drop_in_place() on the inner data. This can cause a use-after-free when
the other revoker's caller proceeds to drop adjacent resources that
drop_in_place() still references (e.g., Devres<DmaMappedSgt> racing with
SGTable freeing the backing sg_table and pages).

Fix this by adding a Completion. The release callback signals the
Completion after revoke() finishes, and Devres::drop() waits for it when
it loses the is_available swap. This ensures the wrapped object is fully
torn down before Devres::drop() returns.

The Linux kernel CVE team has assigned CVE-2026-89764 to this issue.


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

	Issue introduced in 6.18 with commit 05aa6fb1c21d7fb9df735da24096d793223789d5 and fixed in 7.2.4 with commit c7e3d57c705ab1053a6a1bbef96795e792da1540
	Issue introduced in 6.18 with commit 05aa6fb1c21d7fb9df735da24096d793223789d5 and fixed in 7.3-rc1 with commit acc516dfa1972d31836b50abc0115216cd0fccc5

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-2026-89764
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:
	rust/kernel/devres.rs


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/c7e3d57c705ab1053a6a1bbef96795e792da1540
	https://git.kernel.org/stable/c/acc516dfa1972d31836b50abc0115216cd0fccc5