Hi Johan,

On Mon, Nov 08 2021, Johan Hovold wrote:

Commit 761ed4a94582 ("tty: serial_core: convert uart_close to use tty_port_close") converted serial core to use tty_port_close() but failed to notice that the transmit buffer still needs to be freed on final close.

Not freeing the transmit buffer means that the buffer is no longer cleared on next open so that any ioctl() waiting for the buffer to drain might wait indefinitely (e.g. on termios changes) or that stale data can end up being transmitted in case tx is restarted.

Furthermore, the buffer of any port that has been opened would leak on driver unbind.

Note that the port lock is held when clearing the buffer pointer due to the ldisc race worked around by commit a5ba1d95e46e ("uart: fix race between uart_put_char() and uart_shutdown()").

Also note that the tty-port shutdown() callback is not called for console ports so it is not strictly necessary to free the buffer page after releasing the lock (cf. d72402145ace ("tty/serial: do not free trasnmit buffer page under port lock")).

Reported-by: Baruch Siach baruch@tkos.co.il Link: https://lore.kernel.org/r/319321886d97c456203d5c6a576a5480d07c3478.163578168... Fixes: 761ed4a94582 ("tty: serial_core: convert uart_close to use tty_port_close") Cc: stable@vger.kernel.org # 4.9 Cc: Rob Herring robh@kernel.org Signed-off-by: Johan Hovold johan@kernel.org

Thanks for the analysis and root cause fix. This patch also fixes the issue for me.

Tested-by: Baruch Siach baruch@tkos.co.il

baruch

---

drivers/tty/serial/serial_core.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c index 0e2e35ab64c7..58834698739c 100644 --- a/drivers/tty/serial/serial_core.c +++ b/drivers/tty/serial/serial_core.c @@ -1542,6 +1542,7 @@ static void uart_tty_port_shutdown(struct tty_port *port) { struct uart_state *state = container_of(port, struct uart_state, port); struct uart_port *uport = uart_port_check(state);

• char *buf;

/* * At this point, we stop accepting input. To do this, we @@ -1563,8 +1564,18 @@ static void uart_tty_port_shutdown(struct tty_port *port) */ tty_port_set_suspended(port, 0);

• uart_change_pm(state, UART_PM_STATE_OFF);

• /*

• * Free the transmit buffer.
  

• */
  

• spin_lock_irq(&uport->lock);
• buf = state->xmit.buf;
• state->xmit.buf = NULL;
• spin_unlock_irq(&uport->lock);

• if (buf)

• free_page((unsigned long)buf);
  

• uart_change_pm(state, UART_PM_STATE_OFF);

} static void uart_wait_until_sent(struct tty_struct *tty, int timeout)