CVE-2026-80758: futex: Avoid private hash use-after-free on final put

CVE-2026-80758: futex: Avoid private hash use-after-free on final put

[Greg Kroah-Hartman]

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

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

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

futex: Avoid private hash use-after-free on final put

futex_private_hash_put() drops the reference to fph before evaluating
fph->mm for wake_up_var(). futex_ref_put() enables preemption again before
returning. If that put drops the final reference and the task is preempted,
another task can pivot to the replacement hash and free the old hash after
an RCU grace period. The first task then reads fph->mm from the freed
allocation when it resumes.

KASAN reports a slab-use-after-free in futex_private_hash_put(), with the
read at offset 24 in a freed kmalloc-512 allocation. The allocation and
free stacks point to futex_hash_allocate() and the RCU free path,
respectively.

Load the mm pointer while the fph reference is still held and pass the
saved value to wake_up_var(). wake_up_var() uses the pointer as a waitqueue
key and does not dereference the mm through it.

The Linux kernel CVE team has assigned CVE-2026-80758 to this issue.


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

	Issue introduced in 6.16 with commit bd54df5ea7cadac520e346d5f0fe5d58e635b6ba and fixed in 6.18.47 with commit dba60d26e9dda3e157ad6b0934d4232f6c6904ee
	Issue introduced in 6.16 with commit bd54df5ea7cadac520e346d5f0fe5d58e635b6ba and fixed in 7.1.11 with commit 12cd315a7b6a7d7db3f69d98bfe3909275e9451d
	Issue introduced in 6.16 with commit bd54df5ea7cadac520e346d5f0fe5d58e635b6ba and fixed in 7.2.1 with commit 25408c62ed4ebcd491d0e9e4b4a5b512547512e4
	Issue introduced in 6.16 with commit bd54df5ea7cadac520e346d5f0fe5d58e635b6ba and fixed in 7.3-rc1 with commit 1c7efabfbaf796f11000a46094a69955a01ec6cc

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-2026-80758
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:
	kernel/futex/core.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/dba60d26e9dda3e157ad6b0934d4232f6c6904ee
	https://git.kernel.org/stable/c/12cd315a7b6a7d7db3f69d98bfe3909275e9451d
	https://git.kernel.org/stable/c/25408c62ed4ebcd491d0e9e4b4a5b512547512e4
	https://git.kernel.org/stable/c/1c7efabfbaf796f11000a46094a69955a01ec6cc