4.1-stable review patch. If anyone has any objections, please let me know.
------------------
From: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>
commit e144c58cad6667876173dd76977e9e6557e34941 upstream.
While closing, new rx data may be received after the input buffers
have been flushed but before stop_rx() halts receiving [1]. The
new data might not be processed by flush_to_ldisc() until after
uart_shutdown() and normal input processing is re-enabled (ie.,
tty->closing = 0). The race is outlined below:
CPU 0 | CPU 1
|
uart_close() |
tty_port_close_start() |
tty->closing = 1 |
tty_ldisc_flush() |
| => IRQ
| while (LSR & data ready)
| uart_insert_char()
| tty_flip_buffer_push()
| <= EOI
stop_rx() | .
uart_shutdown() | .
free xmit.buf | .
tty_port_tty_set(NULL) | .
tty->closing = 0 | .
| flush_to_ldisc()
| n_tty_receive_buf_common()
| __receive_buf()
| ...
| commit_echoes()
| uart_flush_chars()
| __uart_start()
| ** OOPS on port.tty deref **
tty_ldisc_flush() |
Input processing must be prevented from echoing (tty->closing = 1)
until _after_ the input buffers have been flushed again at the end
of uart_close().
[1] In fact, some input may actually be buffered _after_ stop_rx()
since the rx interrupt may have already triggered but not yet been
handled when stop_rx() disables rx interrupts.
Fixes: 2e758910832d ("serial: core: Flush ldisc after dropping port
mutex in uart_close()")
Reported-by: Robert Elliott <elliott@xxxxxx>
Signed-off-by: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/tty/serial/serial_core.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -1409,7 +1409,7 @@ static void uart_close(struct tty_struct
mutex_lock(&port->mutex);
uart_shutdown(tty, state);
tty_port_tty_set(port, NULL);
- tty->closing = 0;
+
spin_lock_irqsave(&port->lock, flags);
if (port->blocked_open) {
@@ -1435,6 +1435,7 @@ static void uart_close(struct tty_struct
mutex_unlock(&port->mutex);
tty_ldisc_flush(tty);
+ tty->closing = 0;
}
static void uart_wait_until_sent(struct tty_struct *tty, int timeout)
--
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