CVE-2026-64292: iommufd: Move vevent memory allocation outside spinlock

CVE-2026-64292: iommufd: Move vevent memory allocation outside spinlock

[Greg Kroah-Hartman]

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

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

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.

The Linux kernel CVE team has assigned CVE-2026-64292 to this issue.


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

	Issue introduced in 6.15 with commit e36ba5ab808ef6237c3148d469c8238674230e2b and fixed in 6.18.40 with commit 779480ea79551c31964e74b9aef0e730faa3aa11
	Issue introduced in 6.15 with commit e36ba5ab808ef6237c3148d469c8238674230e2b and fixed in 7.1.4 with commit 6c5fc40200cd0a87d66a368eee00df4d1cca946e
	Issue introduced in 6.15 with commit e36ba5ab808ef6237c3148d469c8238674230e2b and fixed in 7.2-rc1 with commit 47443565d10c51366c9382dbc8597cd6c460b8a2

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-2026-64292
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:
	drivers/iommu/iommufd/driver.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/779480ea79551c31964e74b9aef0e730faa3aa11
	https://git.kernel.org/stable/c/6c5fc40200cd0a87d66a368eee00df4d1cca946e
	https://git.kernel.org/stable/c/47443565d10c51366c9382dbc8597cd6c460b8a2