tty: Fix transient pty write() EIO

Commit 699390354da6c258b65bf8fa79cfd5feaede50b6
('pty: Ignore slave pty close() if never successfully opened')
introduced a bug with ptys whereby a write() in parallel with an
open() on an existing pty could mistakenly indicate an I/O error.

Only indicate an I/O error if the condition on open() actually exists.

Reported-by: Markus Trippelsdorf <markus@trippelsdorf.de>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Tested-by: Mikael Pettersson <mikpe@it.uu.se>
Cc: stable <stable@vger.kernel.org> # 3.9
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 5 insertions, 8 deletions

diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
index 59bfaecc4e14..abfd99089781 100644
--- a/drivers/tty/pty.c
+++ b/drivers/tty/pty.c
@@ -244,14 +244,9 @@ static void pty_flush_buffer(struct tty_struct *tty)
 
 static int pty_open(struct tty_struct *tty, struct file *filp)
 {
-        int     retval = -ENODEV;
-
         if (!tty || !tty->link)
-                goto out;
-
-        set_bit(TTY_IO_ERROR, &tty->flags);
+                return -ENODEV;
 
-        retval = -EIO;
         if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
                 goto out;
         if (test_bit(TTY_PTY_LOCK, &tty->link->flags))
@@ -262,9 +257,11 @@ static int pty_open(struct tty_struct *tty, struct file *filp)
         clear_bit(TTY_IO_ERROR, &tty->flags);
         clear_bit(TTY_OTHER_CLOSED, &tty->link->flags);
         set_bit(TTY_THROTTLED, &tty->flags);
-        retval = 0;
+        return 0;
+
 out:
-        return retval;
+        set_bit(TTY_IO_ERROR, &tty->flags);
+        return -EIO;
 }
 
 static void pty_set_termios(struct tty_struct *tty,