[PATCH] nfc: st-nci: Fix use after free bug in ndlc_remove due to race condition

[Zheng Wang]

This bug influences both st_nci_i2c_remove and st_nci_spi_remove.
Take st_nci_i2c_remove as an example.

In st_nci_i2c_probe, it called ndlc_probe and bound &ndlc->sm_work
with llt_ndlc_sm_work.

When it calls ndlc_recv or timeout handler, it will finally call
schedule_work to start the work.

When we call st_nci_i2c_remove to remove the driver, there
may be a sequence as follows:

Fix it by finishing the work before cleanup in ndlc_remove

CPU0                  CPU1

                    |llt_ndlc_sm_work
st_nci_i2c_remove   |
  ndlc_remove       |
     st_nci_remove  |
     nci_free_device|
     kfree(ndev)    |
//free ndlc->ndev   |
                    |llt_ndlc_rcv_queue
                    |nci_recv_frame
                    |//use ndlc->ndev

Fixes: 35630df68d60 ("NFC: st21nfcb: Add driver for STMicroelectronics ST21NFCB NFC chip")
Signed-off-by: Zheng Wang <zyytlz.wz@xxxxxxx>
---
 drivers/nfc/st-nci/ndlc.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/nfc/st-nci/ndlc.c b/drivers/nfc/st-nci/ndlc.c
index 755460a73c0d..d2aa9f766738 100644
--- a/drivers/nfc/st-nci/ndlc.c
+++ b/drivers/nfc/st-nci/ndlc.c
@@ -282,13 +282,15 @@ EXPORT_SYMBOL(ndlc_probe);
 
 void ndlc_remove(struct llt_ndlc *ndlc)
 {
-	st_nci_remove(ndlc->ndev);
-
 	/* cancel timers */
 	del_timer_sync(&ndlc->t1_timer);
 	del_timer_sync(&ndlc->t2_timer);
 	ndlc->t2_active = false;
 	ndlc->t1_active = false;
+	/* cancel work */
+	cancel_work_sync(&ndlc->sm_work);
+
+	st_nci_remove(ndlc->ndev);
 
 	skb_queue_purge(&ndlc->rcv_q);
 	skb_queue_purge(&ndlc->send_q);
-- 
2.25.1