USB: serial: fix missing locking on fifo in write callback

On errors the fifo was reset without any locking. This could race with
write which do kfifo_put and perhaps also chars_in_buffer and write_room.

Every other access to the fifo is protected using the port lock so
better add it to the error path as well.

Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 5 insertions, 2 deletions

diff --git a/drivers/usb/serial/generic.c b/drivers/usb/serial/generic.c
index 8f78d7b8e888..2a3196a2c66c 100644
--- a/drivers/usb/serial/generic.c
+++ b/drivers/usb/serial/generic.c
@@ -519,10 +519,13 @@ void usb_serial_generic_write_bulk_callback(struct urb *urb)
                 port->write_urb_busy = 0;
                 spin_unlock_irqrestore(&port->lock, flags);
 
-                if (status)
+                if (status) {
+                        spin_lock_irqsave(&port->lock, flags);
                         kfifo_reset_out(&port->write_fifo);
-                else
+                        spin_unlock_irqrestore(&port->lock, flags);
+                } else {
                         usb_serial_generic_write_start(port);
+                }
         }
 
         if (status)