CVE-2026-64588: fuse-uring: fix data races on ring->ready

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

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

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

fuse-uring: fix data races on ring->ready

On weakly-ordered architectures, the store to fiq->ops can be
reordered past the store to ring->ready, allowing a CPU that sees
ring->ready == true via fuse_uring_ready() to dispatch requests
through a stale fiq->ops pointer. Upgrade the store to
smp_store_release() and the load in fuse_uring_ready() to
smp_load_acquire() so that the preceding WRITE_ONCE(fiq->ops, ...)
is visible to any CPU that observes ring->ready == true.

Additionally, fuse_uring_do_register() publishes ring->ready with
WRITE_ONCE() but the fast-path check reads it with a plain load.
This is a marked-vs-unmarked access that KCSAN will flag. Wrap it in
READ_ONCE() to mark it without adding unnecessary ordering.

Also wrap the fc->ring load in fuse_uring_ready() in READ_ONCE() to
prevent the compiler from reloading it between the NULL check and the
dereference.

The Linux kernel CVE team has assigned CVE-2026-64588 to this issue.


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

	Issue introduced in 6.14 with commit c2c9af9a0b13261c36909036057a116f2edb5e1a and fixed in 6.18.39 with commit b156bb9966972122b148acab8bdf415cdb8176a3
	Issue introduced in 6.14 with commit c2c9af9a0b13261c36909036057a116f2edb5e1a and fixed in 7.1.4 with commit d01a09b442cb786cd44ccc7c84d57e2856d6737c
	Issue introduced in 6.14 with commit c2c9af9a0b13261c36909036057a116f2edb5e1a and fixed in 7.2-rc1 with commit 46725a0056c884cf58a6897f222892807327d82d

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-2026-64588
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:
	fs/fuse/dev_uring.c
	fs/fuse/dev_uring_i.h


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/b156bb9966972122b148acab8bdf415cdb8176a3
	https://git.kernel.org/stable/c/d01a09b442cb786cd44ccc7c84d57e2856d6737c
	https://git.kernel.org/stable/c/46725a0056c884cf58a6897f222892807327d82d