CVE-2026-80859: fuse: fix missing barrier when checking io-uring readiness

CVE-2026-80859: fuse: fix missing barrier when checking io-uring readiness

[Greg Kroah-Hartman]

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

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

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

fuse: fix missing barrier when checking io-uring readiness

fuse_block_alloc() reads fch->initialized and then fch->io_uring.
fch->io_uring is set before fch->initialized, ordered by the smp_wmb()
in fuse_chan_set_intialized(), but fuse_block_alloc() has no matching
read barrier between the two loads.

This may lead a CPU to observe fch->initialized=1 but fch->io_uring=0,
and skip the check that blocks request allocation until the io-uring
queues are ready. This can reintroduce the lock-order inversion deadlock
that commit 3393ff964e0f prevents.

Add an smp_rmb() barrier to pair with the smp_wmb() in
fuse_chan_set_initialized() to prevent this.

The Linux kernel CVE team has assigned CVE-2026-80859 to this issue.


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

	Issue introduced in 6.14 with commit 3393ff964e0fa5def66570c54a4612bf9df06b76 and fixed in 7.2.3 with commit dd9c835709f4bb3e4256eea7573e4e6e18f956de
	Issue introduced in 6.14 with commit 3393ff964e0fa5def66570c54a4612bf9df06b76 and fixed in 7.3-rc1 with commit edb310bc27f0ad83e7fd558a3caf1a94ca511654

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-2026-80859
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.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/dd9c835709f4bb3e4256eea7573e4e6e18f956de
	https://git.kernel.org/stable/c/edb310bc27f0ad83e7fd558a3caf1a94ca511654