CVE-2026-74398ipv6: addrconf: bail out of dad_failure when state is no longer POSTDAD

Official description

In the Linux kernel, the following vulnerability has been resolved: ipv6: addrconf: bail out of dad_failure when state is no longer POSTDAD addrconf_dad_failure() transitions ifp->state from DAD to POSTDAD via addrconf_dad_end(), which drops ifp->lock on return. The lock is re-acquired after net_info_ratelimited(). A concurrent ipv6_del_addr() can take the lock in that window, set ifp->state to DEAD and run list_del_rcu(&ifp->if_list). addrconf_dad_failure() then overwrites DEAD with ERRDAD at errdad: and schedules a new dad_work. The work calls ipv6_del_addr() again, hitting the already-poisoned list entry: general protection fault: 0000 [#1] SMP NOPTI CPU: 4 PID: 217 Comm: kworker/4:1 Workqueue: ipv6_addrconf addrconf_dad_work RIP: 0010:ipv6_del_addr+0xe9/0x280 RAX: dead000000000122 Call Trace: addrconf_dad_stop+0x113/0x140 addrconf_dad_work+0x28c/0x430 process_one_work+0x1eb/0x3b0 worker_thread+0x4d/0x400 kthread+0x104/0x140 ret_from_fork+0x35/0x40 Fold the addrconf_dad_end() logic into addrconf_dad_failure() under a single ifp->lock critical section. The STABLE_PRIVACY branch temporarily drops ifp->lock around address regeneration, so at lock_errdad: verify the state is still POSTDAD before transitioning to ERRDAD; bail out otherwise to avoid overwriting a state set by another path while the lock was released.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/47b05836705b63dab93d9ac7c69a3a507375ef80
• https://git.kernel.org/stable/c/d21be7d051012c6b572fa4e3334443c250216f7b
• https://git.kernel.org/stable/c/875c284c0f98b042bb97abad460f63a24c977f88
• https://git.kernel.org/stable/c/8ed0ce9ea58d677d1bac92614ee5f60f8ea57363
• https://git.kernel.org/stable/c/3bdc86d89fd6c6523753fa6f42fcfaf30ee699cb
• https://git.kernel.org/stable/c/b61af0268e3d1308c466bf0be5dced844eafc1ef
• https://git.kernel.org/stable/c/e889aa99ad3ed48bb0ddcff6475b17542532d18b
• https://git.kernel.org/stable/c/627ac78f2741e2ebd2225e2e953b6964a8a9182f