CVE-2026-74465: net: openvswitch: fix potential UAF on meter attach failure

CVE-2026-74465: net: openvswitch: fix potential UAF on meter attach failure

[Greg Kroah-Hartman]

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

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

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

net: openvswitch: fix potential UAF on meter attach failure

While attaching a newly created meter attach_meter() function makes
the new meter visible to other CPUs but can still fail afterwards.
On failure, it detaches the meter back and returns an error.

However, this is an unexpected behavior for the ovs_meter_cmd_set()
that uses a plain kfree(meter) on attach failure without waiting for
RCU readers to stop using it, assuming it was never visible.

This is never a problem for ovs-vswitchd as it always creates meters
before creating any flows that use them.  But the UAF can be triggered
with a custom application using uAPI:

 BUG: KASAN: slab-use-after-free in ovs_meter_execute (net/openvswitch/meter.c:653)
 Read of size 8 at addr ffff88810d152650 by task meter/2508

 Call Trace:
  ovs_meter_execute (net/openvswitch/meter.c:653)
  do_execute_actions (net/openvswitch/actions.c:1407)
  ovs_execute_actions (net/openvswitch/actions.c:1584)
  ovs_packet_cmd_execute (net/openvswitch/datapath.c:703)
  ...
  netlink_sendmsg (af_netlink.c:1900)

 Allocated by task 2519:
  __kasan_kmalloc (mm/kasan/common.c:398 mm/kasan/common.c:415)
  ovs_meter_cmd_set (net/openvswitch/meter.c:422)
  ...
  netlink_sendmsg (af_netlink.c:1900)

 Freed by task 2519:
  kfree (mm/slub.c:2705 mm/slub.c:6405 mm/slub.c:6720)
  ovs_meter_cmd_set (net/openvswitch/meter.c:479)
  ...
  netlink_sendmsg (af_netlink.c:1900)

Fix that by making sure attach_meter() doesn't make the meter visible
until all the checks are done and the function can't fail anymore.

This also makes sure the "hash" value is calculated after the potential
re-sizing of the table.

Reported by Trend Micro's Zero Day Initiative as ZDI-CAN-31642.

The Linux kernel CVE team has assigned CVE-2026-74465 to this issue.


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

	Issue introduced in 5.8 with commit c7c4c44c9a95d87e50ced38f7480e779cb472174 and fixed in 6.6.151 with commit 0310d1fa7f9debd0d89629e9f14c7975a47eaa9a
	Issue introduced in 5.8 with commit c7c4c44c9a95d87e50ced38f7480e779cb472174 and fixed in 6.12.103 with commit 4d03e5fa3fbb1df15258a1eb3d6963f0d65659b3
	Issue introduced in 5.8 with commit c7c4c44c9a95d87e50ced38f7480e779cb472174 and fixed in 6.18.44 with commit 90623c9499627803ef3f04fa25a3199402d4fb95
	Issue introduced in 5.8 with commit c7c4c44c9a95d87e50ced38f7480e779cb472174 and fixed in 7.1.8 with commit 431a295d93f76fbdb6a7cfce92a9e3dfee1e5d61
	Issue introduced in 5.8 with commit c7c4c44c9a95d87e50ced38f7480e779cb472174 and fixed in 7.2-rc6 with commit a58a2b0ce354df531ebc71fc870058c2feb59f6b

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-2026-74465
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:
	net/openvswitch/meter.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/0310d1fa7f9debd0d89629e9f14c7975a47eaa9a
	https://git.kernel.org/stable/c/4d03e5fa3fbb1df15258a1eb3d6963f0d65659b3
	https://git.kernel.org/stable/c/90623c9499627803ef3f04fa25a3199402d4fb95
	https://git.kernel.org/stable/c/431a295d93f76fbdb6a7cfce92a9e3dfee1e5d61
	https://git.kernel.org/stable/c/a58a2b0ce354df531ebc71fc870058c2feb59f6b