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 --- v5: At lock_errdad, check for any state other than POSTDAD instead of only DEAD, to avoid overwriting a state set while the lock was released (suggested by Ido Schimmel). Update subject and last commit message paragraph accordingly. v4: Move the bail-out from errdad: to right after lock_errdad: re-acquires ifp->lock, since DAD failure path needs the state transition to ERRDAD (suggested by Paolo Abeni). v3: Fold addrconf_dad_end() into addrconf_dad_failure() under a single ifp->lock critical section, instead of adding a check at errdad: with a racy state inspection (suggested by Sabrina Dubroca). v2: Add Fixes: tag. v1: https://lore.kernel.org/netdev/20260420032842.1063277-1-lilinmao@kylinos.cn/ net/ipv6/addrconf.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c index 5476b6536eb7..da0f07e21e3f 100644 --- a/net/ipv6/addrconf.c +++ b/net/ipv6/addrconf.c @@ -2166,16 +2166,18 @@ void addrconf_dad_failure(struct sk_buff *skb, struct inet6_ifaddr *ifp) struct net *net = dev_net(idev->dev); int max_addresses; - if (addrconf_dad_end(ifp)) { + spin_lock_bh(&ifp->lock); + + if (ifp->state != INET6_IFADDR_STATE_DAD) { + spin_unlock_bh(&ifp->lock); in6_ifa_put(ifp); return; } + ifp->state = INET6_IFADDR_STATE_POSTDAD; net_info_ratelimited("%s: IPv6 duplicate address %pI6c used by %pM detected!\n", ifp->idev->dev->name, &ifp->addr, eth_hdr(skb)->h_source); - spin_lock_bh(&ifp->lock); - if (ifp->flags & IFA_F_STABLE_PRIVACY) { struct in6_addr new_addr; struct inet6_ifaddr *ifp2; @@ -2223,6 +2225,11 @@ void addrconf_dad_failure(struct sk_buff *skb, struct inet6_ifaddr *ifp) in6_ifa_put(ifp2); lock_errdad: spin_lock_bh(&ifp->lock); + if (ifp->state != INET6_IFADDR_STATE_POSTDAD) { + spin_unlock_bh(&ifp->lock); + in6_ifa_put(ifp); + return; + } } errdad: -- 2.25.1