From: Alexey Kardashevskiy <aik@xxxxxxxxx> commit 2f70e49ed860020f5abae4f7015018ebc10e1f0e upstream. At the moment opening a serial device node (such as /dev/ttyS3) succeeds even if there is no actual serial device behind it. Reading/writing/ioctls fail as expected because the uart port is not initialized (the type is PORT_UNKNOWN) and the TTY_IO_ERROR error state bit is set fot the tty. However setting line discipline does not have these checks 8250_port.c (8250 is the default choice made by univ8250_console_init()). As the result of PORT_UNKNOWN, uart_port::iobase is NULL which a platform translates onto some address accessing which produces a crash like below. This adds tty_port_initialized() to uart_set_ldisc() to prevent the crash. Found by syzkaller. Signed-off-by: Alexey Kardashevskiy <aik@xxxxxxxxx> Link: https://lore.kernel.org/r/20201203055834.45838-1-aik@xxxxxxxxx Cc: stable <stable@xxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/tty/serial/serial_core.c | 4 ++++ 1 file changed, 4 insertions(+) --- a/drivers/tty/serial/serial_core.c +++ b/drivers/tty/serial/serial_core.c @@ -1465,6 +1465,10 @@ static void uart_set_ldisc(struct tty_st { struct uart_state *state = tty->driver_data; struct uart_port *uport; + struct tty_port *port = &state->port; + + if (!tty_port_initialized(port)) + return; mutex_lock(&state->port.mutex); uport = uart_port_check(state);
