Subject: [PATCH net v4] 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 to struct udp_bearer and take it around the list_add_rcu() in
tipc_udp_rcast_add() and the list_del_rcu() loop in cleanup_bearer() so the
two writers can no longer corrupt the list.

Reject a duplicate peer under the same lock before allocating, and remove
tipc_udp_is_known_peer(). The old lockless pre-check in
tipc_udp_rcast_disc() was racy: two softirqs discovering the same peer could
both find it absent and add it twice. Doing the check under rcast_lock in
tipc_udp_rcast_add(), before the allocation, makes it the single point of truth
for both the discovery and the netlink add paths and keeps a flood of the same
address from churning the allocator.

Fixes: ef20cd4dd163 ("tipc: introduce UDP replicast")
Reported-by: Xiang Mei <redacted>
Suggested-by: Tung Nguyen <redacted>
Signed-off-by: Weiming Shi <redacted>
---
v4: (per Tung's review)
- Reject a duplicate under rcast_lock before allocating rcast, so a
  flood of the same address can't churn the allocator.
v3:
- Check for a duplicate peer in tipc_udp_rcast_add() under rcast_lock
  and remove tipc_udp_is_known_peer().
v2:
- Narrow the lock to the list mutation.

net/tipc/udp_media.c | 53 ++++++++++++++++++++------------------------
1 file changed, 24 insertions(+), 29 deletions(-)

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

62ae7f5b5..3f0d75d72 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:	serialize updates to @rcast.list against concurrent

updaters
 */
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) @@ -278,26
+280,6 @@ static int tipc_udp_send_msg(struct net *net, struct sk_buff *skb,
	return err;
}

-static bool tipc_udp_is_known_peer(struct tipc_bearer *b,
-				   struct udp_media_addr *addr)
-{
-	struct udp_replicast *rcast, *tmp;
-	struct udp_bearer *ub;
-
-	ub = rcu_dereference_rtnl(b->media_ptr);
-	if (!ub) {
-		pr_err_ratelimited("UDP bearer instance not found\n");
-		return false;
-	}
-
-	list_for_each_entry_safe(rcast, tmp, &ub->rcast.list, list) {
-		if (!memcmp(&rcast->addr, addr, sizeof(struct
udp_media_addr)))
-			return true;
-	}
-
-	return false;
-}
-
static int tipc_udp_rcast_add(struct tipc_bearer *b,
			      struct udp_media_addr *addr)
{

@@ -308,16 +290,34 @@ static int tipc_udp_rcast_add(struct tipc_bearer *b,

	if (!ub)
		return -ENODEV;

+	/* Serialize with other updaters and reject a duplicate before
+	 * allocating, so a flood of the same address can't churn the
+	 * allocator.
+	 */
+	spin_lock_bh(&ub->rcast_lock);
+	list_for_each_entry(rcast, &ub->rcast.list, list) {
+		if (!memcmp(&rcast->addr, addr, sizeof(*addr))) {
+			spin_unlock_bh(&ub->rcast_lock);
+			return 0;
+		}
+	}
+
	rcast = kmalloc_obj(*rcast, GFP_ATOMIC);
-	if (!rcast)
+	if (!rcast) {
+		spin_unlock_bh(&ub->rcast_lock);
		return -ENOMEM;
+	}

	if (dst_cache_init(&rcast->dst_cache, GFP_ATOMIC)) {
+		spin_unlock_bh(&ub->rcast_lock);
		kfree(rcast);
		return -ENOMEM;
	}

	memcpy(&rcast->addr, addr, sizeof(struct udp_media_addr));
+	list_add_rcu(&rcast->list, &ub->rcast.list);
+	b->bcast_addr.broadcast = TIPC_REPLICAST_SUPPORT;
+	spin_unlock_bh(&ub->rcast_lock);

	if (ntohs(addr->proto) == ETH_P_IP)
		pr_info("New replicast peer: %pI4\n", &rcast->addr.ipv4); @@
-325,8 +325,6 @@ static int tipc_udp_rcast_add(struct tipc_bearer *b,
	else if (ntohs(addr->proto) == ETH_P_IPV6)
		pr_info("New replicast peer: %pI6\n", &rcast->addr.ipv6);
#endif
-	b->bcast_addr.broadcast = TIPC_REPLICAST_SUPPORT;
-	list_add_rcu(&rcast->list, &ub->rcast.list);
	return 0;
}

@@ -361,9 +359,6 @@ static int tipc_udp_rcast_disc(struct tipc_bearer *b,

struct sk_buff *skb)
		return 0;
	}

-	if (likely(tipc_udp_is_known_peer(b, &src)))
-		return 0;
-
	return tipc_udp_rcast_add(b, &src);
}

@@ -644,9 +639,6 @@ int tipc_udp_nl_bearer_add(struct tipc_bearer *b,

struct nlattr *attr)
		return -EINVAL;
	}

-	if (tipc_udp_is_known_peer(b, &addr))
-		return 0;
-
	return tipc_udp_rcast_add(b, &addr);
}

@@ -679,6 +671,7 @@ 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 +812,12 @@ 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