linux-kernel - [PATCH -next v2 06/26] pty: Always return -EIO if slave BSD pty opened first

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Date:	Wed,  5 Nov 2014 12:12:49 -0500
From:	Peter Hurley <peter@...leysoftware.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Jiri Slaby <jslaby@...e.cz>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
	Peter Hurley <peter@...leysoftware.com>
Subject: [PATCH -next v2 06/26] pty: Always return -EIO if slave BSD pty opened first

Opening the slave BSD pty first already returns -EIO from the slave
pty_open(), which in turn causes the newly installed tty pair to be
released before returning from tty_open(). However, this can also
cause a parallel master BSD pty open to fail because the pty pair
destruction may already been taking place in tty_release().

Failing at driver->install() if the slave pty is opened first ensures
that a pty master open cannot fail, because the driver tables will
not have been updated so tty_driver_lookup_tty() won't find the
master pty (and attempt to "re-open" it).

In turn, this guarantees that any tty with a tty->count == 0 is
in final close (rather than never opened).

Reviewed-by: Alan Cox <alan@...ux.intel.com>
Signed-off-by: Peter Hurley <peter@...leysoftware.com>
---
 drivers/tty/pty.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
index 7a1a538..bdb8fd1 100644
--- a/drivers/tty/pty.c
+++ b/drivers/tty/pty.c
@@ -383,6 +383,10 @@ static int pty_common_install(struct tty_driver *driver, struct tty_struct *tty,
 	int idx = tty->index;
 	int retval = -ENOMEM;
 
+	/* Opening the slave first has always returned -EIO */
+	if (driver->subtype != PTY_TYPE_MASTER)
+		return -EIO;
+
 	ports[0] = kmalloc(sizeof **ports, GFP_KERNEL);
 	ports[1] = kmalloc(sizeof **ports, GFP_KERNEL);
 	if (!ports[0] || !ports[1])
@@ -419,8 +423,6 @@ static int pty_common_install(struct tty_driver *driver, struct tty_struct *tty,
 	 * Everything allocated ... set up the o_tty structure.
 	 */
 	tty_driver_kref_get(driver->other);
-	if (driver->subtype == PTY_TYPE_MASTER)
-		o_tty->count++;
 	/* Establish the links in both directions */
 	tty->link   = o_tty;
 	o_tty->link = tty;
@@ -432,6 +434,7 @@ static int pty_common_install(struct tty_driver *driver, struct tty_struct *tty,
 
 	tty_driver_kref_get(driver);
 	tty->count++;
+	o_tty->count++;
 	return 0;
 err_free_termios:
 	if (legacy)
-- 
2.1.3

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