From d966ddcc38217a6110a6a0ff37ad2dee7d42e23e Mon Sep 17 00:00:00 2001 From: Hoang Huu Le Date: Mon, 7 Sep 2020 13:17:25 +0700 Subject: tipc: fix a deadlock when flushing scheduled work In the commit fdeba99b1e58 ("tipc: fix use-after-free in tipc_bcast_get_mode"), we're trying to make sure the tipc_net_finalize_work work item finished if it enqueued. But calling flush_scheduled_work() is not just affecting above work item but either any scheduled work. This has turned out to be overkill and caused to deadlock as syzbot reported: ====================================================== WARNING: possible circular locking dependency detected 5.9.0-rc2-next-20200828-syzkaller #0 Not tainted ------------------------------------------------------ kworker/u4:6/349 is trying to acquire lock: ffff8880aa063d38 ((wq_completion)events){+.+.}-{0:0}, at: flush_workqueue+0xe1/0x13e0 kernel/workqueue.c:2777 but task is already holding lock: ffffffff8a879430 (pernet_ops_rwsem){++++}-{3:3}, at: cleanup_net+0x9b/0xb10 net/core/net_namespace.c:565 [...] Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(pernet_ops_rwsem); lock(&sb->s_type->i_mutex_key#13); lock(pernet_ops_rwsem); lock((wq_completion)events); *** DEADLOCK *** [...] v1: To fix the original issue, we replace above calling by introducing a bit flag. When a namespace cleaned-up, bit flag is set to zero and: - tipc_net_finalize functionial just does return immediately. - tipc_net_finalize_work does not enqueue into the scheduled work queue. v2: Use cancel_work_sync() helper to make sure ONLY the tipc_net_finalize_work() stopped before releasing bcbase object. Reported-by: syzbot+d5aa7e0385f6a5d0f4fd@syzkaller.appspotmail.com Fixes: fdeba99b1e58 ("tipc: fix use-after-free in tipc_bcast_get_mode") Acked-by: Jon Maloy Signed-off-by: Hoang Huu Le Signed-off-by: Jakub Kicinski --- net/tipc/core.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) (limited to 'net/tipc/core.c') diff --git a/net/tipc/core.c b/net/tipc/core.c index 37d8695548cf..c2ff42900b53 100644 --- a/net/tipc/core.c +++ b/net/tipc/core.c @@ -60,6 +60,7 @@ static int __net_init tipc_init_net(struct net *net) tn->trial_addr = 0; tn->addr_trial_end = 0; tn->capabilities = TIPC_NODE_CAPABILITIES; + INIT_WORK(&tn->final_work.work, tipc_net_finalize_work); memset(tn->node_id, 0, sizeof(tn->node_id)); memset(tn->node_id_string, 0, sizeof(tn->node_id_string)); tn->mon_threshold = TIPC_DEF_MON_THRESHOLD; @@ -107,13 +108,13 @@ out_crypto: static void __net_exit tipc_exit_net(struct net *net) { + struct tipc_net *tn = tipc_net(net); + tipc_detach_loopback(net); + /* Make sure the tipc_net_finalize_work() finished */ + cancel_work_sync(&tn->final_work.work); tipc_net_stop(net); - /* Make sure the tipc_net_finalize_work stopped - * before releasing the resources. - */ - flush_scheduled_work(); tipc_bcast_stop(net); tipc_nametbl_stop(net); tipc_sk_rht_destroy(net); -- cgit v1.2.3