syzbot is reporting attempt to schedule hdev->cmd_work work from system_wq
WQ into hdev->workqueue WQ which is under draining operation [1], for
commit c8efcc2589464ac7 ("workqueue: allow chained queueing during
destruction") does not allow such operation.
The check introduced by commit 877afadad2dce8aa ("Bluetooth: When HCI work
queue is drained, only queue chained work") was incomplete.
Use hdev->workqueue WQ when queuing hdev->{cmd,ncmd}_timer works because
hci_{cmd,ncmd}_timeout() calls queue_work(hdev->workqueue). Also, protect
the queuing operation with RCU read lock in order to avoid calling
queue_delayed_work() after cancel_delayed_work() completed.
Link: https://syzkaller.appspot.com/bug?extid=243b7d89777f90f7613b [1]
Reported-by: syzbot <syzbot+243b7d89777f90f7613b@xxxxxxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Fixes: 877afadad2dce8aa ("Bluetooth: When HCI work queue is drained, only queue chained work")
---
This is a difficult to trigger race condition, and therefore reproducer is
not available. Please do logical check in addition to automated testing.
net/bluetooth/hci_core.c | 15 +++++++++++++--
net/bluetooth/hci_event.c | 6 ++++--
2 files changed, 17 insertions(+), 4 deletions(-)
diff --git a/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c
index b3a5a3cc9372..9873d2e67988 100644
--- a/net/bluetooth/hci_core.c
+++ b/net/bluetooth/hci_core.c
@@ -597,6 +597,15 @@ static int hci_dev_do_reset(struct hci_dev *hdev)
/* Cancel these to avoid queueing non-chained pending work */
hci_dev_set_flag(hdev, HCI_CMD_DRAIN_WORKQUEUE);
+ /* Wait for
+ *
+ * if (!hci_dev_test_flag(hdev, HCI_CMD_DRAIN_WORKQUEUE))
+ * queue_delayed_work(&hdev->{cmd,ncmd}_timer)
+ *
+ * inside RCU section to see the flag or complete scheduling.
+ */
+ synchronize_rcu();
+ /* Explicitly cancel works in case scheduled after setting the flag. */
cancel_delayed_work(&hdev->cmd_timer);
cancel_delayed_work(&hdev->ncmd_timer);
@@ -4056,12 +4065,14 @@ static void hci_cmd_work(struct work_struct *work)
if (res < 0)
__hci_cmd_sync_cancel(hdev, -res);
+ rcu_read_lock();
if (test_bit(HCI_RESET, &hdev->flags) ||
hci_dev_test_flag(hdev, HCI_CMD_DRAIN_WORKQUEUE))
cancel_delayed_work(&hdev->cmd_timer);
else
- schedule_delayed_work(&hdev->cmd_timer,
- HCI_CMD_TIMEOUT);
+ queue_delayed_work(hdev->workqueue, &hdev->cmd_timer,
+ HCI_CMD_TIMEOUT);
+ rcu_read_unlock();
} else {
skb_queue_head(&hdev->cmd_q, skb);
queue_work(hdev->workqueue, &hdev->cmd_work);
diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
index 6643c9c20fa4..d6f0e6ca0e7e 100644
--- a/net/bluetooth/hci_event.c
+++ b/net/bluetooth/hci_event.c
@@ -3766,16 +3766,18 @@ static inline void handle_cmd_cnt_and_timer(struct hci_dev *hdev, u8 ncmd)
{
cancel_delayed_work(&hdev->cmd_timer);
+ rcu_read_lock();
if (!test_bit(HCI_RESET, &hdev->flags)) {
if (ncmd) {
cancel_delayed_work(&hdev->ncmd_timer);
atomic_set(&hdev->cmd_cnt, 1);
} else {
if (!hci_dev_test_flag(hdev, HCI_CMD_DRAIN_WORKQUEUE))
- schedule_delayed_work(&hdev->ncmd_timer,
- HCI_NCMD_TIMEOUT);
+ queue_delayed_work(hdev->workqueue, &hdev->ncmd_timer,
+ HCI_NCMD_TIMEOUT);
}
}
+ rcu_read_unlock();
}
static u8 hci_cc_le_read_buffer_size_v2(struct hci_dev *hdev, void *data,
--
2.18.4
