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    Subject[PATCH 4.19 090/346] serial_core: Check for port state when tty is in error state
    Date
    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(+)

    --- 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_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);

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