staging: fwserial: fix TIOCSSERIAL permission check

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>

diff --git a/drivers/staging/fwserial/fwserial.c b/drivers/staging/fwserial/fwserial.c
index c963848..440d114 100644 (file)
--- a/drivers/staging/fwserial/fwserial.c
+++ b/drivers/staging/fwserial/fwserial.c
@@ -1232,20 +1232,24 @@ static int set_serial_info(struct tty_struct *tty,
                           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;