CVE-2026-64263: fuse-uring: fix moving cancelled entry to ent_in_userspace list

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

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

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

fuse-uring: fix moving cancelled entry to ent_in_userspace list

fuse_uring_cancel() moves entries that are available (these have no reqs
attached) to the ent_in_userspace list. ent_list_request_expired()
checks the first entry on ent_in_userspace and dereferences
ent->fuse_req unconditionally, which will crash on a cancelled entry
that was moved to this list.

Fix this by freeing the entry and dropping queue_refs directly in
fuse_uring_cancel(). This is safe because cancel is the cancel handler
itself - after io_uring_cmd_done(), no more cancels will be dispatched
for this command, and teardown serializes with cancel via queue->lock.

Since cancel now decrements queue_refs, fuse_uring_abort() must no
longer gate fuse_uring_abort_end_requests() on queue_refs > 0, as
cancelled entries may have already dropped queue_refs while requests are
still queued. Remove the gate so abort always flushes requests and stops
queues.

The Linux kernel CVE team has assigned CVE-2026-64263 to this issue.


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

	Issue introduced in 6.16 with commit 4fea593e625cd50d4d11be227007849b12f17bfb and fixed in 6.18.39 with commit 50f3e03db823cabc41fe35c27d77c2bdb112baad
	Issue introduced in 6.16 with commit 4fea593e625cd50d4d11be227007849b12f17bfb and fixed in 7.1.4 with commit e8afc85acdf329361b2d8df2ad9b52364686235f
	Issue introduced in 6.16 with commit 4fea593e625cd50d4d11be227007849b12f17bfb and fixed in 7.2-rc1 with commit 198f45eeb9f78b2a2d6d8be95e4e43468eb2c6bc

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-2026-64263
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/50f3e03db823cabc41fe35c27d77c2bdb112baad
	https://git.kernel.org/stable/c/e8afc85acdf329361b2d8df2ad9b52364686235f
	https://git.kernel.org/stable/c/198f45eeb9f78b2a2d6d8be95e4e43468eb2c6bc