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    Subject[PATCH 5.4 013/244] staging: fwserial: fix TIOCSSERIAL permission check
    Date
    From: Johan Hovold <johan@kernel.org>

    commit 2104eb283df66a482b60254299acbe3c68c03412 upstream.

    Changing the port close-delay parameter is a privileged operation so
    make sure to return -EPERM if a regular user tries to change it.

    Fixes: 7355ba3445f2 ("staging: fwserial: Add TTY-over-Firewire serial driver")
    Cc: stable@vger.kernel.org # 3.8
    Signed-off-by: Johan Hovold <johan@kernel.org>
    Link: https://lore.kernel.org/r/20210407102334.32361-3-johan@kernel.org
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/staging/fwserial/fwserial.c | 8 ++++++--
    1 file changed, 6 insertions(+), 2 deletions(-)

    --- a/drivers/staging/fwserial/fwserial.c
    +++ b/drivers/staging/fwserial/fwserial.c
    @@ -1232,20 +1232,24 @@ static int set_serial_info(struct tty_st
    struct serial_struct *ss)
    {
    struct fwtty_port *port = tty->driver_data;
    + unsigned int cdelay;

    if (ss->irq != 0 || ss->port != 0 || ss->custom_divisor != 0 ||
    ss->baud_base != 400000000)
    return -EPERM;

    + cdelay = msecs_to_jiffies(ss->close_delay * 10);
    +
    mutex_lock(&port->port.mutex);
    if (!capable(CAP_SYS_ADMIN)) {
    - if (((ss->flags & ~ASYNC_USR_MASK) !=
    + if (cdelay != port->port.close_delay ||
    + ((ss->flags & ~ASYNC_USR_MASK) !=
    (port->port.flags & ~ASYNC_USR_MASK))) {
    mutex_unlock(&port->port.mutex);
    return -EPERM;
    }
    }
    - port->port.close_delay = msecs_to_jiffies(ss->close_delay * 10);
    + port->port.close_delay = cdelay;
    mutex_unlock(&port->port.mutex);

    return 0;

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