From: Alexey Kardashevskiy aik@ozlabs.ru
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@ozlabs.ru Link: https://lore.kernel.org/r/20201203055834.45838-1-aik@ozlabs.ru Cc: stable stable@vger.kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/tty/serial/serial_core.c | 4 ++++ 1 file changed, 4 insertions(+)
diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c index 2a5bf4c14fb8..80fa06b16d9d 100644 --- a/drivers/tty/serial/serial_core.c +++ b/drivers/tty/serial/serial_core.c @@ -1421,6 +1421,10 @@ static void uart_set_ldisc(struct tty_struct *tty) { 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);