sctp_free_addr_wq() previously removed addr_wq_timer using timer_delete()
while holding addr_wq_lock. However, timer_delete() does not guarantee that
a currently running timer handler has completed.

This allows a race with sctp_addr_wq_timeout_handler(), where the handler
may still run after addr_waitq has been freed, acquire addr_wq_lock, and
access freed memory, leading to a use-after-free.

Fix this by calling timer_shutdown_sync() before taking addr_wq_lock.  This
guarantees that any in-flight timer handler has finished and prevents the
timer from being re-armed during teardown, making subsequent cleanup safe.

Fixes: 4db67e808640 ("sctp: Make the address lists per network namespace")
Reported-by: Sashiko <sashiko-bot@kernel.org>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
---
 net/sctp/protocol.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/sctp/protocol.c b/net/sctp/protocol.c
index 587b0017a67d..cf335494bffe 100644
--- a/net/sctp/protocol.c
+++ b/net/sctp/protocol.c

@@ -663,8 +663,9 @@ static void sctp_free_addr_wq(struct net *net)
 	struct sctp_sockaddr_entry *addrw;
 	struct sctp_sockaddr_entry *temp;
 
+	timer_shutdown_sync(&net->sctp.addr_wq_timer);
+
 	spin_lock_bh(&net->sctp.addr_wq_lock);
-	timer_delete(&net->sctp.addr_wq_timer);
 	list_for_each_entry_safe(addrw, temp, &net->sctp.addr_waitq, list) {
 		list_del(&addrw->list);
 		kfree(addrw);

-- 
2.47.1