Subject: [PATCH net] tipc: serialize udp bearer replicast list updates

tipc_udp_rcast_add() and cleanup_bearer() both update ub->rcast.list with
list_add_rcu() / list_del_rcu(), but nothing serializes them. The add runs from
the encap receive softirq (via tipc_udp_rcast_disc()) without rtnl_lock(), so it
can race the cleanup delete and corrupt the
list:

list_del corruption. prev->next should be ffff8880298d7ab8,
  but was ffff88802449ad38. (prev=ffff888027e3ec98)  kernel BUG at
lib/list_debug.c:62!
RIP: __list_del_entry_valid_or_report+0x17a/0x200
Workqueue: events cleanup_bearer
Call Trace:
 cleanup_bearer (net/tipc/udp_media.c:811)
 process_one_work (kernel/workqueue.c:3302)
 worker_thread (kernel/workqueue.c:3466)

The bearer can be enabled from an unprivileged user namespace, as the
TIPCv2 generic-netlink ops carry no GENL_ADMIN_PERM.

Add a spinlock and take it around both list updates. Re-check for the peer
under the lock in the add path so the check-then-add in
tipc_udp_rcast_disc() cannot insert a duplicate.

Fixes: ef20cd4dd163 ("tipc: introduce UDP replicast")
Reported-by: Xiang Mei <redacted>
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Weiming Shi <redacted>
---
net/tipc/udp_media.c | 19 ++++++++++++++++++-
1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/net/tipc/udp_media.c b/net/tipc/udp_media.c index

62ae7f5b5840..601174297a16 100644

--- a/net/tipc/udp_media.c
+++ b/net/tipc/udp_media.c

@@ -94,6 +94,7 @@ struct udp_replicast {
 * @ifindex:	local address scope
 * @work:	used to schedule deferred work on a bearer
 * @rcast:	associated udp_replicast container
+ * @rcast_lock:	serializes updates to @rcast.list
 */

struct udp_bearer {
	struct tipc_bearer __rcu *bearer;

@@ -101,6 +102,7 @@ struct udp_bearer {

	u32 ifindex;
	struct work_struct work;
	struct udp_replicast rcast;
+	spinlock_t rcast_lock; /* protects rcast.list */
};

static int tipc_udp_is_mcast_addr(struct udp_media_addr *addr) @@ -301,7
+303,7 @@ static bool tipc_udp_is_known_peer(struct tipc_bearer *b,  static
int tipc_udp_rcast_add(struct tipc_bearer *b,
			      struct udp_media_addr *addr)
{
-	struct udp_replicast *rcast;
+	struct udp_replicast *rcast, *tmp;
	struct udp_bearer *ub;

	ub = rcu_dereference_rtnl(b->media_ptr);

@@ -319,6 +321,17 @@ static int tipc_udp_rcast_add(struct tipc_bearer *b,

	memcpy(&rcast->addr, addr, sizeof(struct udp_media_addr));

+	/* tipc_udp_rcast_disc() adds from softirq without rtnl_lock(). */

+
	if (ntohs(addr->proto) == ETH_P_IP)
		pr_info("New replicast peer: %pI4\n", &rcast->addr.ipv4);  #if
IS_ENABLED(CONFIG_IPV6) @@ -327,6 +340,7 @@ static int
tipc_udp_rcast_add(struct tipc_bearer *b,  #endif
	b->bcast_addr.broadcast = TIPC_REPLICAST_SUPPORT;
	list_add_rcu(&rcast->list, &ub->rcast.list);
+	spin_unlock_bh(&ub->rcast_lock);
	return 0;
}

@@ -679,6 +693,7 @@ static int tipc_udp_enable(struct net *net, struct

tipc_bearer *b,
		return -ENOMEM;

	INIT_LIST_HEAD(&ub->rcast.list);
+	spin_lock_init(&ub->rcast_lock);

	if (!attrs[TIPC_NLA_BEARER_UDP_OPTS])
		goto err;

@@ -819,10 +834,12 @@ static void cleanup_bearer(struct work_struct

*work)
	struct udp_replicast *rcast, *tmp;
	struct tipc_net *tn;

+	spin_lock_bh(&ub->rcast_lock);
	list_for_each_entry_safe(rcast, tmp, &ub->rcast.list, list) {
		list_del_rcu(&rcast->list);
		call_rcu_hurry(&rcast->rcu, rcast_free_rcu);
	}
+	spin_unlock_bh(&ub->rcast_lock);

	tn = tipc_net(sock_net(ub->sk));

--
2.43.0