There is a race condition for accessing hu->tx_skb between
hci_uart_flush() and hci_uart_dequeue() which runs in
hci_uart_write_work() from the work queue hu->write_work. This race
condition exists because there is no locking between these 2 threads
to protect hu->tx_skb. Consequently a call to hci_uart_flush() might
be able to free hu->tx_skb whilst hci_uart_write_work() is using
hu->tx_skb which is undesirable as a crash could occur.
Performing any flushing in the transmission path between the Data Link
protocol layer and the UART port may corrupt the data. So freeing
hu->tx_skb or not freeing hu->tx_skb makes little difference to having
intact data or corrupted data. So it is OK not to free hu->tx_skb.
Instead, move the freeing of hu->tx_skb to the end of
hci_uart_tty_close() from hci_uart_flush(). This eliminates the race
condition because the Data Link protocol layer is in the unbound state
and ensures hu->tx_skb is freed before hu is freed. Also use a temporary
pointer to allow hu->tx_skb to be set to NULL before freeing hu->tx_skb.
Signed-off-by: Dean Jenkins <Dean_Jenkins@xxxxxxxxxx>
---
drivers/bluetooth/hci_ldisc.c | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)
diff --git a/drivers/bluetooth/hci_ldisc.c b/drivers/bluetooth/hci_ldisc.c
index 236c8e7..fbf830a 100644
--- a/drivers/bluetooth/hci_ldisc.c
+++ b/drivers/bluetooth/hci_ldisc.c
@@ -237,10 +237,6 @@ static int hci_uart_flush(struct hci_dev *hdev)
BT_DBG("hdev %p tty %p", hdev, tty);
- if (hu->tx_skb) {
- kfree_skb(hu->tx_skb); hu->tx_skb = NULL;
- }
-
/* Flush any pending characters in the driver and discipline. */
tty_ldisc_flush(tty);
tty_driver_flush_buffer(tty);
@@ -510,6 +506,7 @@ static void hci_uart_tty_close(struct tty_struct *tty)
struct hci_uart *hu = tty->disc_data;
struct hci_dev *hdev;
unsigned long flags;
+ struct sk_buff *temp_skb;
BT_DBG("tty %p", tty);
@@ -546,6 +543,12 @@ static void hci_uart_tty_close(struct tty_struct *tty)
hci_free_dev(hdev);
}
+ if (hu->tx_skb) {
+ temp_skb = hu->tx_skb;
+ hu->tx_skb = NULL;
+ kfree_skb(temp_skb);
+ }
+
kfree(hu);
}
--
2.7.4
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