tipc_node_find_by_name() returns a node after dropping its RCU read lock without taking a reference. The LINK_SET, LINK_GET and LINK_RESET_STATS handlers then lock and access the node, racing with timer-driven cleanup of a down peer. Generic netlink serialization does not exclude the node timer. The following interleaving can leave a handler using a freed node: CPU 0: find the node under RCU and release the node read lock CPU 1: tipc_node_timeout() clears the links and unlinks the down node CPU 1: drop the list and timer references, queuing tipc_node_free() CPU 0: leave the RCU read-side critical section CPU 1: complete the grace period and free the node CPU 0: acquire the node lock through the stale pointer LINK_SET also uses the node's media address after releasing the node lock, when passing queued packets to tipc_bearer_xmit(). KASAN on v7.3-rc5 reported: BUG: KASAN: slab-use-after-free in _raw_read_lock_bh Write of size 4 at addr ffff88807e06f008 by task poc/92 Call Trace: _raw_read_lock_bh kernel/locking/spinlock.c:287 tipc_nl_node_set_link net/tipc/node.c:2475 genl_family_rcv_msg_doit net/netlink/genetlink.c:1114 genl_rcv_msg net/netlink/genetlink.c:1209 netlink_rcv_skb net/netlink/af_netlink.c:2575 Allocated by task 0: tipc_node_create net/tipc/node.c:539 tipc_node_check_dest net/tipc/node.c:1196 tipc_disc_rcv net/tipc/discover.c:252 Freed by task 92: kfree mm/slub.c:6801 rcu_core kernel/rcu/tree.c:2919 Last potentially related work creation: __call_rcu_common.constprop.0 kernel/rcu/tree.c:3181 tipc_node_timeout net/tipc/node.c:814 Acquire a reference to the selected node with kref_get_unless_zero() before leaving RCU, returning NULL if the node has already been released. Release that reference on every caller exit after the last node access, including transmission in LINK_SET. Keep the existing link lookup order and locking so concurrent link removal still takes the existing error paths. Fixes: 6a939f365bdb ("tipc: Auto removal of peer down node instance") Cc: stable@vger.kernel.org Signed-off-by: Chengfeng Ye --- Changes in v2: - Take the node reference inside the matching-node block, as suggested by Tung Quang Nguyen. - Reproduce the UAF on v7.3-rc5 and include a decoded KASAN trace. Link: https://lore.kernel.org/r/20260927064036.3691962-1-nicoyip.dev@gmail.com/ [v1] net/tipc/node.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/net/tipc/node.c b/net/tipc/node.c index bd91378b7540..d7cbfa786c13 100644 --- a/net/tipc/node.c +++ b/net/tipc/node.c @@ -2421,8 +2421,11 @@ static struct tipc_node *tipc_node_find_by_name(struct net *net, } } tipc_node_read_unlock(n); - if (found_node) + if (found_node) { + if (!kref_get_unless_zero(&found_node->kref)) + found_node = NULL; break; + } } rcu_read_unlock(); @@ -2507,6 +2510,7 @@ int tipc_nl_node_set_link(struct sk_buff *skb, struct genl_info *info) tipc_node_read_unlock(node); tipc_bearer_xmit(net, bearer_id, &xmitq, &node->links[bearer_id].maddr, NULL); + tipc_node_put(node); return res; } @@ -2558,12 +2562,14 @@ int tipc_nl_node_get_link(struct sk_buff *skb, struct genl_info *info) link = node->links[bearer_id].link; if (!link) { tipc_node_read_unlock(node); + tipc_node_put(node); err = -EINVAL; goto err_free; } err = __tipc_nl_add_link(net, &msg, link, 0); tipc_node_read_unlock(node); + tipc_node_put(node); if (err) goto err_free; } @@ -2634,11 +2640,13 @@ int tipc_nl_node_reset_link_stats(struct sk_buff *skb, struct genl_info *info) if (!link) { spin_unlock_bh(&le->lock); tipc_node_read_unlock(node); + tipc_node_put(node); return -EINVAL; } tipc_link_reset_stats(link); spin_unlock_bh(&le->lock); tipc_node_read_unlock(node); + tipc_node_put(node); return 0; } -- 2.43.0