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. Check for a duplicate peer under the same lock before adding, 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() makes it the single point of truth for both the discovery and the netlink add paths. Fixes: ef20cd4dd163 ("tipc: introduce UDP replicast") Reported-by: Xiang Mei Suggested-by: Tung Nguyen Signed-off-by: Weiming Shi Assisted-by: Claude:claude-opus-4-8 --- v3: (per Tung's review) - Check for a duplicate peer in tipc_udp_rcast_add() under rcast_lock before adding, and remove tipc_udp_is_known_peer(). - This also drops the list_for_each_entry_rcu() change to tipc_udp_is_known_peer() from v2, since the helper is gone. v2: - Narrow the lock to the list mutation. net/tipc/udp_media.c | 45 ++++++++++++++++++-------------------------- 1 file changed, 18 insertions(+), 27 deletions(-) diff --git a/net/tipc/udp_media.c b/net/tipc/udp_media.c index 62ae7f5b5..3a7d9b15c 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) @@ -278,30 +280,10 @@ 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) { - struct udp_replicast *rcast; + struct udp_replicast *rcast, *tmp; struct udp_bearer *ub; ub = rcu_dereference_rtnl(b->media_ptr); @@ -326,7 +308,19 @@ static int tipc_udp_rcast_add(struct tipc_bearer *b, pr_info("New replicast peer: %pI6\n", &rcast->addr.ipv6); #endif b->bcast_addr.broadcast = TIPC_REPLICAST_SUPPORT; + + /* serialize with other updaters and drop duplicates under the lock */ + spin_lock_bh(&ub->rcast_lock); + list_for_each_entry(tmp, &ub->rcast.list, list) { + if (!memcmp(&tmp->addr, addr, sizeof(*addr))) { + spin_unlock_bh(&ub->rcast_lock); + dst_cache_destroy(&rcast->dst_cache); + kfree(rcast); + return 0; + } + } list_add_rcu(&rcast->list, &ub->rcast.list); + spin_unlock_bh(&ub->rcast_lock); return 0; } @@ -361,9 +355,6 @@ 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 +635,6 @@ 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 +667,7 @@ 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 +808,12 @@ 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