CVE-2026-64259: fuse-uring: make a fuse_req on SQE commit only findable after memcpy

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

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

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

fuse-uring: make a fuse_req on SQE commit only findable after memcpy

Bad userspace might try to trick us and send commit SQEs request
unique / commit-id of requests that are not even send to
fuse-server (io_uring_cmd_done() not called) yet.

fuse_uring_commit_fetch() ends the fuse request when the ring entry
has a wrong state, but that could have caused a use-after-free
with the memcpy operations in fuse_uring_send_in_task().
In order to avoid such races the call of fuse_uring_add_to_pq()
is moved after the copy operations and just before completing
the io-uring request - malicious userspace cannot find the request
anymore until all prepration work in fuse-client/kernel is completed.

This also moves fuse_uring_add_to_pq() a bit up in the code to
avoid a forward declaration. Also not with a preparation commit,
to make it easier to back port to older kernels.

The Linux kernel CVE team has assigned CVE-2026-64259 to this issue.


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

	Issue introduced in 6.14 with commit c090c8abae4b6b77a1bee116aa6c385456ebef96 and fixed in 6.18.39 with commit e1711479e9068ea31b31353a702a51e639c3d059
	Issue introduced in 6.14 with commit c090c8abae4b6b77a1bee116aa6c385456ebef96 and fixed in 7.1.4 with commit a635f427d57e2012102ae4886b48d8955c59fb86
	Issue introduced in 6.14 with commit c090c8abae4b6b77a1bee116aa6c385456ebef96 and fixed in 7.2-rc1 with commit 1efd3d474fc0ba74dfd984249bca78807d739812

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-2026-64259
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


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/e1711479e9068ea31b31353a702a51e639c3d059
	https://git.kernel.org/stable/c/a635f427d57e2012102ae4886b48d8955c59fb86
	https://git.kernel.org/stable/c/1efd3d474fc0ba74dfd984249bca78807d739812