[PATCH 5.4 46/54] tipc: fix a deadlock when flushing scheduled work

Greg Kroah-Hartman
2020-12-10T15:31:40Z

From: Hoang Huu Le <hoang.h.le@dektech.com.au>

commit d966ddcc38217a6110a6a0ff37ad2dee7d42e23e upstream.

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 <jmaloy@redhat.com>
Signed-off-by: Hoang Huu Le <hoang.h.le@dektech.com.au>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
net/tipc/core.c | 9 +++++----
net/tipc/core.h | 9 +++++++++
net/tipc/net.c | 20 +++++---------------
net/tipc/net.h | 1 +
4 files changed, 20 insertions(+), 19 deletions(-)

--- a/net/tipc/core.c
+++ b/net/tipc/core.c
@@ -59,6 +59,7 @@ static int __net_init tipc_init_net(stru
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;
@@ -96,13 +97,13 @@ out_sk_rht:

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);
--- a/net/tipc/core.h
+++ b/net/tipc/core.h
@@ -86,6 +86,12 @@ extern unsigned int tipc_net_id __read_m
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;
@@ -134,6 +140,9 @@ struct tipc_net {

/* Tracing of node internal messages */
struct packet_type loopback_pt;
+
+ /* Work item for net finalize */
+ struct tipc_net_work final_work;
};

static inline struct tipc_net *tipc_net(struct net *net)
--- a/net/tipc/net.c
+++ b/net/tipc/net.c
@@ -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
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)
--- a/net/tipc/net.h
+++ b/net/tipc/net.h
@@ -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);