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.h | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'net/tipc/core.h') diff --git a/net/tipc/core.h b/net/tipc/core.h index 631d83c9705f..1d57a4d3b05e 100644 --- a/net/tipc/core.h +++ b/net/tipc/core.h @@ -90,6 +90,12 @@ extern unsigned int tipc_net_id __read_mostly; extern int sysctl_tipc_rmem[3] __read_mostly; extern int sysctl_tipc_named_timeout __read_mostly; +struct tipc_net_work { + struct work_struct work; + struct net *net; + u32 addr; +}; + struct tipc_net { u8 node_id[NODE_ID_LEN]; u32 node_addr; @@ -143,6 +149,8 @@ struct tipc_net { /* TX crypto handler */ struct tipc_crypto *crypto_tx; #endif + /* Work item for net finalize */ + struct tipc_net_work final_work; }; static inline struct tipc_net *tipc_net(struct net *net) -- cgit v1.2.3-59-g8ed1b