Medium [CVE-2026-64292] Move vevent memory allocation outside spinlock

In the Linux kernel, the following vulnerability has been resolved: iommufd: Move vevent memory allocation outside spinlock The veventq memory allocation happens inside the spinlock. Given its depth is decided by the user space, this leaves a vulnerability, where userspace can allocate large queues to exhaust atomic memory reserves.

Move the allocation outside the spinlock and use GFP_NOWAIT, which can fail fast under memory pressure without dipping into the GFP_ATOMIC reserves or direct-reclaiming from the threaded IRQ handler.

On allocation failure, queue the lost_events_header (so userspace learns of the drop) and return -ENOMEM so the caller learns of the kernel-side memory pressure.

This is intentionally distinct from the queue-overflow path, which also queues the lost_events_header but returns 0: a full queue is an expected userspace-pacing condition rather than a kernel error. A subsequent change will cap the upper bound of the veventq_depth.

A local user can exploit this vulnerability by allocating large `veventq` queues, which are processed inside a spinlock. This can lead to the exhaustion of atomic memory reserves, resulting in a Denial of Service (DoS) condition.

Red Hat severity: Moderate — CVSS 5.5 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H). Weakness: CWE-770.

Affected Red Hat products: Red Hat Enterprise Linux 10; Red Hat Enterprise Linux 9.