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tipc: fix a deadlock when flushing scheduled work

Browse source 
In the commit fdeba99b1e
("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: fdeba99b1e ("tipc: fix use-after-free in tipc_bcast_get_mode")
Acked-by: Jon Maloy <jmaloy@redhat.com>
Signed-off-by: Hoang Huu Le <hoang.h.le@dektech.com.au>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Hoang Huu Le 2020-09-07 13:17:25 +07:00 • committed by Jakub Kicinski
parent 02a20d4fef
commit d966ddcc38
4 changed files with 19 additions and 19 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

9
net/tipc/core.c
View file

@ -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);

8
net/tipc/core.h
View file

@ -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)

20
net/tipc/net.c
View file

@ -105,12 +105,6 @@
* - A local spin_lock protecting the queue of subscriber events.
*/
struct tipc_net_work {
struct work_struct work;
struct net *net;
u32 addr;
};
static void tipc_net_finalize(struct net *net, u32 addr);
int tipc_net_init(struct net *net, u8 *node_id, u32 addr)
@ -142,25 +136,21 @@ static void tipc_net_finalize(struct net *net, u32 addr)
TIPC_CLUSTER_SCOPE, 0, addr);
}
static void tipc_net_finalize_work(struct work_struct *work)
void tipc_net_finalize_work(struct work_struct *work)
{
struct tipc_net_work *fwork;
fwork = container_of(work, struct tipc_net_work, work);
tipc_net_finalize(fwork->net, fwork->addr);
kfree(fwork);
}
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);
if (!fwork)
return;
INIT_WORK(&fwork->work, tipc_net_finalize_work);
fwork->net = net;
fwork->addr = addr;
schedule_work(&fwork->work);
tn->final_work.net = net;
tn->final_work.addr = addr;
schedule_work(&tn->final_work.work);
}
void tipc_net_stop(struct net *net)

1
net/tipc/net.h
View file

@ -42,6 +42,7 @@
extern const struct nla_policy tipc_nl_net_policy[];
int tipc_net_init(struct net *net, u8 *node_id, u32 addr);
void tipc_net_finalize_work(struct work_struct *work);
void tipc_sched_net_finalize(struct net *net, u32 addr);
void tipc_net_stop(struct net *net);
int tipc_nl_net_dump(struct sk_buff *skb, struct netlink_callback *cb);