tty: Prevent hw state corruption in exclusive mode reopen

Exclusive mode ttys (TTY_EXCLUSIVE) do not allow further reopens;
fail the condition before associating the file pointer and calling
the driver open() method.

Prevents DTR programming when the tty is already in exclusive mode.

Reported-by: Shreyas Bethur <shreyas.bethur@ni.com>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Acked-by: Shreyas Bethur <shreyas.bethur@ni.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 4f35b43..51f066a 100644 (file)
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -1464,6 +1464,9 @@ static int tty_reopen(struct tty_struct *tty)
            driver->subtype == PTY_TYPE_MASTER)
                return -EIO;
 
+       if (test_bit(TTY_EXCLUSIVE, &tty->flags) && !capable(CAP_SYS_ADMIN))
+               return -EBUSY;
+
        tty->count++;
 
        WARN_ON(!tty->ldisc);
@@ -2106,10 +2109,6 @@ retry_open:
                retval = -ENODEV;
        filp->f_flags = saved_flags;
 
-       if (!retval && test_bit(TTY_EXCLUSIVE, &tty->flags) &&
-                                               !capable(CAP_SYS_ADMIN))
-               retval = -EBUSY;
-
        if (retval) {
 #ifdef TTY_DEBUG_HANGUP
                printk(KERN_DEBUG "%s: error %d in opening %s...\n", __func__,