xfrm: avoid lock inversion in nat keepalive work

Overview

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

xfrm: avoid lock inversion in nat keepalive work

nat_keepalive_work() walks the state table while xfrm_state_walk() holds net->xfrm.xfrm_state_lock. Its callback then acquires x->lock, which conflicts with the delete path taking the same locks in reverse order via xfrm_state_delete() and __xfrm_state_delete(). This creates an AB-BA deadlock that is reported by lockdep when a NAT keepalive worker races with SA deletion.

Fix this by splitting the keepalive walk into two phases. First, collect the candidate states while the walk holds xfrm_state_lock and take a reference on each state. Then, after the walk completes, process each collected state and acquire x->lock without nesting it under xfrm_state_lock.

Affected

• Linux >= f531d13bdfe3f4f084aaa8acae2cb0f02295f5ae < ea09210462316e5235a25eccb11ad0708d86615e
• Linux >= f531d13bdfe3f4f084aaa8acae2cb0f02295f5ae < 5c86c895d1cac81a71ead3005084c6265cf6a7a5
• Linux >= f531d13bdfe3f4f084aaa8acae2cb0f02295f5ae < 89ef3a2e1e4682ab82b0455ce113f8c39fb9e50d
• Linux >= f531d13bdfe3f4f084aaa8acae2cb0f02295f5ae < a9fa05b7a1246797748d15771052639e0d3cabf1
• Linux >= f531d13bdfe3f4f084aaa8acae2cb0f02295f5ae < 763fe700b7c58ad64fe5202c5638848244dd4127
• Linux 6.11

Remediation

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