Re: [PATCH net v5] ipv6: addrconf: bail out of dad_failure when state is no longer POSTDAD

[Ido Schimmel]

On Wed, May 13, 2026 at 10:55:09AM +0800, Linmao Li wrote:
> 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.
> 
> Fixes: c15b1ccadb32 ("ipv6: move DAD and addrconf_verify processing to workqueue")
> Signed-off-by: Linmao Li <lilinmao@xxxxxxxxxx>

Reviewed-by: Ido Schimmel <idosch@xxxxxxxxxx>