openvswitch: Fix CT limit teardown use-after-free

Overview

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

openvswitch: Fix CT limit teardown use-after-free

Packet processing uses CT limit state under RCU, while netns teardown frees that state under ovs_mutex. The CT limit pointer was neither removed from readers nor protected by a grace period, allowing packet processing to dereference the freed state.

An unprivileged user can trigger this bug from a user and network namespace, causing a slab-use-after-free in ovs_ct_execute() when the netns is torn down.

Publish the CT limit pointer through RCU, remove it before teardown, and wait for readers before freeing its contents. Keep ovs_mutex around individual CT limit updates, and use the RCU read-side lock while GET traverses the RCU-protected limit lists.

Netns teardown detaches the RCU-protected CT limit state in the pernet .pre_exit callback while holding ovs_mutex. The pernet core guarantees an RCU grace period between the .pre_exit and .exit callbacks, so the .exit callback completes the teardown without adding any extra synchronization.

The netlink command handlers do not need NULL checks because the userspace netlink socket holds an active reference to its network namespace while a request is processed. The per-netns exit path therefore cannot run concurrently with SET, DEL, or GET for that socket's namespace.

Affected

• Linux >= 11efd5cb04a184eea4f57b68ea63dddd463158d1 < 239f26589a6926db28c436e14f28517581ef1385
• Linux >= 11efd5cb04a184eea4f57b68ea63dddd463158d1 < 3b9369881b403f4cdbb11fa998554382bdcc3d8c
• Linux >= 11efd5cb04a184eea4f57b68ea63dddd463158d1 < 3b41d907400cc1dd1da9555b81dca422b1f44433
• Linux >= 11efd5cb04a184eea4f57b68ea63dddd463158d1 < 680f20d5937fa4d1367c59fe83091b78041015f5
• Linux >= 11efd5cb04a184eea4f57b68ea63dddd463158d1 < bf4aaa7ea2579e24ed7de2e20578a875bebca011
• Linux >= 11efd5cb04a184eea4f57b68ea63dddd463158d1 < e15407c3a8a005324f633cd46cd8fb58042c1157
• Linux >= 11efd5cb04a184eea4f57b68ea63dddd463158d1 < 6a6d36fadb8537d9b79e72c9fa51885ec0c33e10
• Linux >= 11efd5cb04a184eea4f57b68ea63dddd463158d1 < 403f96c32c9e24600093d7d0c61c17daeedca957
• Linux 4.18

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

Vendor advisories

• Red Hat VEX · Important · affected: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4, Red Hat Enterprise Linux 6 · no fix planned: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4 · updated 2026-09-18 · vex