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>

1 files changed, 3 insertions, 4 deletions

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 4f35b43e2475..51f066aa375e 100644
--- 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__,