[PATCH net v3 1/3] ipv6: serialize address publication with device teardown

[Daehyeon Ko <4ncienth@gmail.com>]

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 later device
deletion waited indefinitely for the leaked references.

Protect the dead indication with idev->lock and keep that lock across
both hash and device-list publication. Use READ_ONCE() for the initial
lockless state checks, then recheck both dead and disable_ipv6 before
publishing. If teardown wins, reject the unpublished object.

Fixes: 8814c4b53381 ("[IPV6] ADDRCONF: Convert addrconf_lock to RCU.")
Cc: stable@vger.kernel.org
Suggested-by: Ido Schimmel <idosch@nvidia.com>
Assisted-by: LLM
Signed-off-by: Daehyeon Ko <4ncienth@gmail.com>
---
 net/ipv6/addrconf.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index c90ee6dd7446cd..77b3b1154d591c 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -1095,13 +1095,13 @@ ipv6_add_addr(struct inet6_dev *idev, struct ifa6_config *cfg,
 		return ERR_PTR(-EADDRNOTAVAIL);
 	}
 
-	if (idev->dead) {
+	if (READ_ONCE(idev->dead)) {
 		NL_SET_ERR_MSG_MOD(extack, "device is going away");
 		err = -ENODEV;
 		goto out;
 	}
 
-	if (idev->cnf.disable_ipv6) {
+	if (READ_ONCE(idev->cnf.disable_ipv6)) {
 		NL_SET_ERR_MSG_MOD(extack, "IPv6 is disabled on this device");
 		err = -EACCES;
 		goto out;
@@ -1168,14 +1168,20 @@ 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 if (READ_ONCE(idev->cnf.disable_ipv6))
+		err = -EACCES;
+	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 +3903,9 @@ 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);
-- 
2.55.0