From: Marco Elver During network namespace teardown, rxrpc_destroy_all_peers() iterates over the rxnet->peer_hash table to print leaked peers. However, it does so without holding rxnet->peer_hash_lock. This allows a race condition with asynchronous peer destruction, where RCU callbacks concurrently remove peers from the hash table and free them. When rxrpc_destroy_all_peers() accesses the freed peer, it results in a KASAN slab-use-after-free. BUG: KASAN: slab-use-after-free in rxrpc_destroy_all_peers+0xcc/0x150 net/rxrpc/peer_object.c:461 Read of size 8 at addr ffff88811089e420 by task kworker/u8:1/13 Call Trace: rxrpc_destroy_all_peers+0xcc/0x150 net/rxrpc/peer_object.c:461 rxrpc_exit_net+0x7f/0xc0 net/rxrpc/net_ns.c:114 ops_exit_list net/core/net_namespace.c:199 [inline] ops_undo_list+0x43d/0x8d0 net/core/net_namespace.c:252 cleanup_net+0x572/0x810 net/core/net_namespace.c:702 process_one_work kernel/workqueue.c:3322 [inline] process_scheduled_works+0xa8e/0x14e0 kernel/workqueue.c:3405 worker_thread+0x92d/0xe10 kernel/workqueue.c:3486 kthread+0x388/0x470 kernel/kthread.c:436 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 To fix the slab-use-after-free, acquire rxnet->peer_hash_lock with spin_lock_bh() while iterating over rxnet->peer_hash in rxrpc_destroy_all_peers(). Additionally, insert rcu_barrier() in rxrpc_exit_net() prior to destroying peers and local endpoints. Without rcu_barrier(), rxrpc_destroy_all_peers() races with pending RCU callbacks that drop peer and local references, logging spurious leak warnings. Furthermore, this missing synchronization causes a downstream panic hazard in rxrpc_destroy_all_locals() because in-flight peer releases leave rxnet->local_endpoints populated. Calling rcu_barrier() ensures all pending RCU callbacks that drop peer and local references complete prior to leak checks and local endpoint destruction. Fixes: 17226f124038 ("rxrpc: Fix leak of rxrpc_peer objects") Assisted-by: Gemini:gemini-3.6-flash Gemini:gemini-3.1-pro-preview syzbot Reported-by: syzbot+c876adfab6362679008c@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=c876adfab6362679008c Link: https://syzkaller.appspot.com/ai_job?id=7fecbeb2-cd9b-4ca2-8149-48663e20b153 Signed-off-by: Marco Elver --- diff --git a/net/rxrpc/net_ns.c b/net/rxrpc/net_ns.c index 9a9834145..c00cddfd3 100644 --- a/net/rxrpc/net_ns.c +++ b/net/rxrpc/net_ns.c @@ -111,6 +111,11 @@ static __net_exit void rxrpc_exit_net(struct net *net) timer_delete_sync(&rxnet->peer_keepalive_timer); rxrpc_destroy_all_calls(rxnet); rxrpc_destroy_all_connections(rxnet); + /* + * Wait for pending RCU callbacks that drop peer and local + * references to avoid spurious leak warnings and panics. + */ + rcu_barrier(); rxrpc_destroy_all_peers(rxnet); rxrpc_destroy_all_locals(rxnet); proc_remove(rxnet->proc_net); diff --git a/net/rxrpc/peer_object.c b/net/rxrpc/peer_object.c index fa9a406e1..32da76256 100644 --- a/net/rxrpc/peer_object.c +++ b/net/rxrpc/peer_object.c @@ -454,6 +454,12 @@ void rxrpc_destroy_all_peers(struct rxrpc_net *rxnet) struct rxrpc_peer *peer; int i; + /* + * The lock is needed to prevent use-after-free if a peer is being + * destroyed concurrently by an RCU callback. + */ + spin_lock_bh(&rxnet->peer_hash_lock); + for (i = 0; i < HASH_SIZE(rxnet->peer_hash); i++) { if (hlist_empty(&rxnet->peer_hash[i])) continue; @@ -465,6 +471,8 @@ void rxrpc_destroy_all_peers(struct rxrpc_net *rxnet) &peer->srx.transport); } } + + spin_unlock_bh(&rxnet->peer_hash_lock); } /** base-commit: db2ddb87143519e20a95aa36c60b36107b736a58 -- See https://goo.gle/syzbot-ai-patches for information about AI-generated patches. The person who has signed off on the patch is responsible for addressing comments. syzbot engineers can be reached at syzkaller@googlegroups.com.