char: moxa, prevent opening unavailable ports

In moxa.c there are 32 minor numbers reserved for each device.  The number
of ports actually available per device is stored in
moxa_board_conf->numPorts.  This number is not considered in moxa_open().
Opening a port that is not available results in a kernel oops.  This patch
adds a test to moxa_open() that prevents opening unavailable ports.

[akpm@linux-foundation.org: avoid multiple returns]
Signed-off-by: Dirk Eibach <eibach@gdsys.de>
Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 6 insertions, 1 deletions

diff --git a/drivers/char/moxa.c b/drivers/char/moxa.c
index 65b6ff2442c6..6799588b0099 100644
--- a/drivers/char/moxa.c
+++ b/drivers/char/moxa.c
@@ -1189,6 +1189,11 @@ static int moxa_open(struct tty_struct *tty, struct file *filp)
                 return -ENODEV;
         }
 
+        if (port % MAX_PORTS_PER_BOARD >= brd->numPorts) {
+                retval = -ENODEV;
+                goto out_unlock;
+        }
+
         ch = &brd->ports[port % MAX_PORTS_PER_BOARD];
         ch->port.count++;
         tty->driver_data = ch;
@@ -1213,8 +1218,8 @@ static int moxa_open(struct tty_struct *tty, struct file *filp)
                                 moxa_close_port(tty);
         } else
                 ch->port.flags |= ASYNC_NORMAL_ACTIVE;
+out_unlock:
         mutex_unlock(&moxa_openlock);
-
         return retval;
 }