From 06227034e2d93942119b922cf05f2de9da0ad848 Mon Sep 17 00:00:00 2001 From: Daehyeon Ko <4ncienth@gmail.com> Date: Thu, 15 Oct 2026 14:06:49 +0900 Subject: [PATCH] ipv6: serialize address publication with device teardown ipv6_add_addr() checks idev state before allocating an ifaddr, but publishes the object later. addrconf_ifdown() can mark and detach the idev between the check and publication. This happens when a non-loopback device MTU falls below IPV6_MIN_MTU. A forced interleaving published an address on a dead idev, and ipv6_get_ifaddr() still returned it after teardown. Later device deletion remained blocked with: unregister_netdevice: waiting for ac0 to become free. Usage count = 3 Protect the dead indication with idev->lock and keep that lock across both hash and device-list publication. Recheck dead before publishing; if teardown wins the lock, reject the unpublished object. Non-unregister teardown does not set dead. The preceding change covers an add that misses the initial hash scan but reaches the per-device list snapshot. Both changes are required when backporting this fix. Fixes: 8814c4b53381 ("[IPV6] ADDRCONF: Convert addrconf_lock to RCU.") Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/179161099408.434549.14449036924552933828@kernel.org Link: https://lore.kernel.org/r/20261012145306.GB779501@shredder Suggested-by: Ido Schimmel Signed-off-by: Daehyeon Ko <4ncienth@gmail.com> Reviewed-by: Ido Schimmel Link: https://patch.msgid.link/20261015050651.1841557-3-4ncienth@gmail.com Signed-off-by: Jakub Kicinski --- net/ipv6/addrconf.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c index 72d7df23f796..3bede30d4e98 100644 --- a/net/ipv6/addrconf.c +++ b/net/ipv6/addrconf.c @@ -1168,14 +1168,18 @@ ipv6_add_addr(struct inet6_dev *idev, struct ifa6_config *cfg, rcu_read_lock(); - err = ipv6_add_addr_hash(idev->dev, ifa); + write_lock_bh(&idev->lock); + + if (idev->dead) + err = -ENODEV; + else + err = ipv6_add_addr_hash(idev->dev, ifa); if (err < 0) { + write_unlock_bh(&idev->lock); rcu_read_unlock(); goto out; } - write_lock_bh(&idev->lock); - /* Add to inet6_dev unicast addr list. */ ipv6_link_dev_addr(idev, ifa); @@ -3897,7 +3901,9 @@ static int addrconf_ifdown(struct net_device *dev, bool unregister) * Do not dev_put! */ if (unregister) { + write_lock_bh(&idev->lock); WRITE_ONCE(idev->dead, 1); + write_unlock_bh(&idev->lock); /* protected by rtnl_lock */ RCU_INIT_POINTER(dev->ip6_ptr, NULL);