CVE-2026-74580: vhost: reset the vring metadata cache on vring reconfiguration

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

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

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

vhost: reset the vring metadata cache on vring reconfiguration

vq->meta_iotlb[] caches the vhost_iotlb_map that backs each vring
metadata region, and iotlb_access_ok() returns early on a cache hit,
taking the hit as proof that the region has already been validated:

	if (vhost_vq_meta_fetch(vq, addr, len, type))
		return true;

The cache is reset on VHOST_IOTLB_UPDATE and VHOST_IOTLB_INVALIDATE, on
device IOTLB (re)initialisation and on vq reset, but not when
VHOST_SET_VRING_ADDR replaces vq->desc, vq->avail and vq->used, nor when
VHOST_SET_VRING_NUM changes the region sizes.

With a device IOTLB attached both ioctls are accepted while the vq is
live, and neither validates the addresses at ioctl time: vq_access_ok()
and vq_log_used_access_ok() return true early because the addresses are
GIOVAs, deferring validation to prefetch time.  Once the cache has been
populated that deferred validation no longer runs -- vq_meta_prefetch()
hits the stale entry and returns true -- and vhost_vq_meta_fetch() keeps
translating through the old mapping as

	map->addr + addr - map->start

for an address the mapping no longer covers.  vhost_copy_to_user() and
vhost_copy_from_user() consume the result with __copy_to_user() and
__copy_from_user(), which do not check it either, so a subsequent used
ring update or descriptor fetch accesses memory outside the region the
IOTLB actually maps.

Reset the metadata cache whenever the vring is reconfigured, so the new
addresses are pushed back through iotlb_access_ok()'s slow path.

The Linux kernel CVE team has assigned CVE-2026-74580 to this issue.


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

	Issue introduced in 4.11 with commit f889491380582b4ba2981cf0b0d7d6a40fb30ab7 and fixed in 5.10.265 with commit 5224bd37e37d36076a550d99b2aebba33939fd95
	Issue introduced in 4.11 with commit f889491380582b4ba2981cf0b0d7d6a40fb30ab7 and fixed in 5.15.216 with commit 54617e9119be2eb728ecdd8d977b99c99d4c498a
	Issue introduced in 4.11 with commit f889491380582b4ba2981cf0b0d7d6a40fb30ab7 and fixed in 6.1.183 with commit 13fa6f32a56a386a82bd7451644c494beed034af
	Issue introduced in 4.11 with commit f889491380582b4ba2981cf0b0d7d6a40fb30ab7 and fixed in 6.6.152 with commit cf363a7a02ce132ef1f58084fdb13e1a3b7da7e7
	Issue introduced in 4.11 with commit f889491380582b4ba2981cf0b0d7d6a40fb30ab7 and fixed in 6.12.104 with commit 6fa3e9b1fe856259555a7e22f3f3082e7827fd9b
	Issue introduced in 4.11 with commit f889491380582b4ba2981cf0b0d7d6a40fb30ab7 and fixed in 6.18.45 with commit f1e21108e3ddfcce62f6cad4ebd7b5674543c9e6
	Issue introduced in 4.11 with commit f889491380582b4ba2981cf0b0d7d6a40fb30ab7 and fixed in 7.1.9 with commit b70ebe0bba254e093dd5fd4c0c170941ce83eb85
	Issue introduced in 4.11 with commit f889491380582b4ba2981cf0b0d7d6a40fb30ab7 and fixed in 7.2 with commit de845981da67a6b049080c87e605130b0c30adc5

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-2026-74580
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/vhost/vhost.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/5224bd37e37d36076a550d99b2aebba33939fd95
	https://git.kernel.org/stable/c/54617e9119be2eb728ecdd8d977b99c99d4c498a
	https://git.kernel.org/stable/c/13fa6f32a56a386a82bd7451644c494beed034af
	https://git.kernel.org/stable/c/cf363a7a02ce132ef1f58084fdb13e1a3b7da7e7
	https://git.kernel.org/stable/c/6fa3e9b1fe856259555a7e22f3f3082e7827fd9b
	https://git.kernel.org/stable/c/f1e21108e3ddfcce62f6cad4ebd7b5674543c9e6
	https://git.kernel.org/stable/c/b70ebe0bba254e093dd5fd4c0c170941ce83eb85
	https://git.kernel.org/stable/c/de845981da67a6b049080c87e605130b0c30adc5