[PATCH] tty: Prevent hw state corruption in exclusive mode reopen

[Peter Hurley <peter@hurleysoftware.com>]

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>
---
 drivers/tty/tty_io.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 4f35b43..8629087 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -2091,6 +2091,11 @@ retry_open:
 		goto err_file;
 	}
 
+	if (test_bit(TTY_EXCLUSIVE, &tty->flags) && !capable(CAP_SYS_ADMIN)) {
+		retval = -EBUSY;
+		goto err_file;
+	}
+
 	tty_add_file(tty, filp);
 
 	check_tty_count(tty, __func__);
@@ -2106,10 +2111,6 @@ 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__,
-- 
2.2.1