[PATCH net v2 2/2] tipc: serialize publication purging with name table updates

[Chengfeng Ye <nicoyip.dev@gmail.com>]

tipc_publ_notify() walks a failed node publication list after the node lock
has been released. Its safe iterator is not protected by nametbl_lock,
which is acquired only inside tipc_publ_purge().

A concurrent withdrawal can unlink and schedule the saved next publication
for freeing. The purge iterator then advances to that removed publication.
It may access freed memory after the RCU grace period, or repeatedly follow
the self-linked binding_node before then.

The decoded causal stack is:

  tipc_nametbl_remove_publ net/tipc/name_table.c:543
  tipc_publ_purge          net/tipc/name_distr.c:244
  tipc_publ_notify         net/tipc/name_distr.c:261
  tipc_node_write_unlock   net/tipc/node.c:425
  tipc_node_link_down      net/tipc/node.c:1094
  tipc_node_delete_links   net/tipc/node.c:1325
  bearer_disable           net/tipc/bearer.c:414
  __tipc_nl_bearer_disable net/tipc/bearer.c:992
  tipc_nl_bearer_disable   net/tipc/bearer.c:1002

Move the failed node publications to a private list under nametbl_lock.
Select, unlink and purge one publication during each lock acquisition, so
no publication pointer is retained across an unlocked interval. Concurrent
withdrawals can remove entries from the private list under the same lock.

Holding the lock for the whole purge would keep bottom halves disabled
while removing every publication. Releasing it after each entry avoids
an excessive lock hold for nodes with many publications.

node_lost_contact() purges queued name-table updates before scheduling the
node-down notification. An update already dequeued by tipc_named_rcv()
holds nametbl_lock until it updates the publication list, so it completes
before the snapshot and is included. A publication accepted after the
snapshot remains on the live node list for a later contact.

Fixes: 9db9fdd1983e ("tipc: avoid to asynchronously notify subscriptions")
Cc: stable@vger.kernel.org

Link: https://lore.kernel.org/netdev/20260927180806.1315902-1-nicoyip.dev@gmail.com/
Signed-off-by: Chengfeng Ye <nicoyip.dev@gmail.com>
---
 net/tipc/name_distr.c | 27 ++++++++++++++++++++-------
 1 file changed, 20 insertions(+), 7 deletions(-)

diff --git a/net/tipc/name_distr.c b/net/tipc/name_distr.c
index acf96562608b..9a400a1fa4d7 100644
--- a/net/tipc/name_distr.c
+++ b/net/tipc/name_distr.c
@@ -230,20 +230,16 @@ void tipc_named_node_up(struct net *net, u32 dnode, u16 capabilities)
  *
  * Invoked for each publication issued by a newly failed node.
  * Removes publication structure from name table & deletes it.
+ * The caller must hold nametbl_lock and unlink the node subscription.
  */
 static void tipc_publ_purge(struct net *net, struct publication *p)
 {
-	struct tipc_net *tn = tipc_net(net);
 	struct publication *_p;
 	struct tipc_uaddr ua;
 
 	tipc_uaddr(&ua, TIPC_SERVICE_RANGE, p->scope, p->sr.type,
 		   p->sr.lower, p->sr.upper);
-	spin_lock_bh(&tn->nametbl_lock);
 	_p = tipc_nametbl_remove_publ(net, &ua, &p->sk, p->key);
-	if (_p)
-		list_del_init(&_p->binding_node);
-	spin_unlock_bh(&tn->nametbl_lock);
 	if (_p)
 		kfree_rcu(_p, rcu);
 }
@@ -254,10 +250,27 @@ void tipc_publ_notify(struct net *net, struct list_head *nsub_list,
 	struct name_table *nt = tipc_name_table(net);
 	struct tipc_net *tn = tipc_net(net);
 
-	struct publication *publ, *tmp;
+	struct publication *publ;
+	LIST_HEAD(purge_list);
 
-	list_for_each_entry_safe(publ, tmp, nsub_list, binding_node)
+	spin_lock_bh(&tn->nametbl_lock);
+	/* Preserve publications learned after this node-down snapshot. */
+	list_splice_init(nsub_list, &purge_list);
+	spin_unlock_bh(&tn->nametbl_lock);
+
+	for (;;) {
+		spin_lock_bh(&tn->nametbl_lock);
+		if (list_empty(&purge_list)) {
+			spin_unlock_bh(&tn->nametbl_lock);
+			break;
+		}
+		publ = list_first_entry(&purge_list, struct publication,
+					binding_node);
+		list_del_init(&publ->binding_node);
 		tipc_publ_purge(net, publ);
+		spin_unlock_bh(&tn->nametbl_lock);
+	}
+
 	spin_lock_bh(&tn->nametbl_lock);
 	if (!(capabilities & TIPC_NAMED_BCAST))
 		nt->rc_dests--;
-- 
2.43.0