Medium [CVE-2026-64263] fix moving cancelled entry to ent_in_userspace list

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.

This vulnerability arises from the incorrect handling of cancelled entries, which are moved to a list where a subsequent operation unconditionally attempts to access a null pointer. A local attacker could exploit this flaw to trigger a system crash, leading to a Denial of Service (DoS).

Red Hat severity: Low — CVSS 5.5 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H). Weakness: CWE-476.