tty: moxa: fix TIOCSSERIAL permission check

Changing the port close delay or type are privileged operations so make
sure to return -EPERM if a regular user tries to change them.

Cc: stable@vger.kernel.org
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20210407102334.32361-12-johan@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/moxa.c b/drivers/tty/moxa.c
index 5b7bc7af8b1e05312761daeccabc50c9a6d34d54..63e440d900ffca9d6f283590b249126c57508d56 100644 (file)
--- a/drivers/tty/moxa.c
+++ b/drivers/tty/moxa.c
@@ -2048,6 +2048,7 @@ static int moxa_set_serial_info(struct tty_struct *tty,
                struct serial_struct *ss)
 {
        struct moxa_port *info = tty->driver_data;
+       unsigned int close_delay;
 
        if (tty->index == MAX_PORTS)
                return -EINVAL;
@@ -2059,19 +2060,24 @@ static int moxa_set_serial_info(struct tty_struct *tty,
                        ss->baud_base != 921600)
                return -EPERM;
 
+       close_delay = msecs_to_jiffies(ss->close_delay * 10);
+
        mutex_lock(&info->port.mutex);
        if (!capable(CAP_SYS_ADMIN)) {
-               if (((ss->flags & ~ASYNC_USR_MASK) !=
+               if (close_delay != info->port.close_delay ||
+                   ss->type != info->type ||
+                   ((ss->flags & ~ASYNC_USR_MASK) !=
                     (info->port.flags & ~ASYNC_USR_MASK))) {
                        mutex_unlock(&info->port.mutex);
                        return -EPERM;
                }
-       }
-       info->port.close_delay = msecs_to_jiffies(ss->close_delay * 10);
+       } else {
+               info->port.close_delay = close_delay;
 
-       MoxaSetFifo(info, ss->type == PORT_16550A);
+               MoxaSetFifo(info, ss->type == PORT_16550A);
 
-       info->type = ss->type;
+               info->type = ss->type;
+       }
        mutex_unlock(&info->port.mutex);
        return 0;
 }