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Date: Mon, 7 Sep 2020 08:22:14 +0000 From: Hoang Huu Le <hoang.h.le@...tech.com.au> To: Jakub Kicinski <kuba@...nel.org> CC: "ying.xue@...driver.com" <ying.xue@...driver.com>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>, "jmaloy@...hat.com" <jmaloy@...hat.com>, "maloy@...jonn.com" <maloy@...jonn.com>, "syzbot+d5aa7e0385f6a5d0f4fd@...kaller.appspotmail.com" <syzbot+d5aa7e0385f6a5d0f4fd@...kaller.appspotmail.com> Subject: RE: [net-next] tipc: fix a deadlock when flushing scheduled work > -----Original Message----- > From: Jakub Kicinski <kuba@...nel.org> > Sent: Monday, September 7, 2020 12:57 AM > To: Hoang Huu Le <hoang.h.le@...tech.com.au> > Cc: ying.xue@...driver.com; netdev@...r.kernel.org; jmaloy@...hat.com; maloy@...jonn.com; > syzbot+d5aa7e0385f6a5d0f4fd@...kaller.appspotmail.com > Subject: Re: [net-next] tipc: fix a deadlock when flushing scheduled work > > On Sat, 5 Sep 2020 11:45:18 +0700 Hoang Huu Le wrote: > > 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 *** > > [...] > > > > 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. > > Is struct tipc_net not going to be freed right after tipc_exit_net() > returns? In that case you'd be back to UAF if the flag is in this > structure. > I rework the fix with version 2. In there, I use cancel_work_sync() API to cancel the specific tipc_net_finalize_work work. > > @@ -110,10 +111,6 @@ static void __net_exit tipc_exit_net(struct net *net) > > tipc_detach_loopback(net); > > 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); > > @@ -124,6 +121,9 @@ static void __net_exit tipc_exit_net(struct net *net) > > > > static void __net_exit tipc_pernet_pre_exit(struct net *net) > > { > > + struct tipc_net *tn = tipc_net(net); > > + > > + clear_bit_unlock(0, &tn->net_exit_flag); > > tipc_node_pre_cleanup_net(net); > > } > > > > diff --git a/net/tipc/core.h b/net/tipc/core.h > > index 631d83c9705f..aa75882dd932 100644 > > --- a/net/tipc/core.h > > +++ b/net/tipc/core.h > > @@ -143,6 +143,7 @@ struct tipc_net { > > /* TX crypto handler */ > > struct tipc_crypto *crypto_tx; > > #endif > > + unsigned long net_exit_flag; > > }; > > > > static inline struct tipc_net *tipc_net(struct net *net) > > diff --git a/net/tipc/net.c b/net/tipc/net.c > > index 85400e4242de..8ad5b9ad89c0 100644 > > --- a/net/tipc/net.c > > +++ b/net/tipc/net.c > > @@ -132,6 +132,9 @@ static void tipc_net_finalize(struct net *net, u32 addr) > > { > > struct tipc_net *tn = tipc_net(net); > > > > + if (unlikely(!test_bit(0, &tn->net_exit_flag))) > > + return; > > + > > if (cmpxchg(&tn->node_addr, 0, addr)) > > return; > > tipc_set_node_addr(net, addr); > > @@ -153,8 +156,13 @@ static void tipc_net_finalize_work(struct work_struct *work) > > > > void tipc_sched_net_finalize(struct net *net, u32 addr) > > { > > - struct tipc_net_work *fwork = kzalloc(sizeof(*fwork), GFP_ATOMIC); > > + struct tipc_net *tn = tipc_net(net); > > + struct tipc_net_work *fwork; > > + > > + if (unlikely(!test_bit(0, &tn->net_exit_flag))) > > + return; > > > > + fwork = kzalloc(sizeof(*fwork), GFP_ATOMIC); > > if (!fwork) > > return; > > INIT_WORK(&fwork->work, tipc_net_finalize_work);
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