[PATCH net v4] tipc: serialize udp bearer replicast list updates
From: Weiming Shi <hidden>
Date: 2026-07-10 17:47:36
Also in:
lkml
Subsystem:
networking [general], the rest, tipc network layer · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds, Jon Maloy
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