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

Peter Hurley
2014-11-05T17:13:39Z

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@linux.intel.com>
Signed-off-by: Peter Hurley <peter@hurleysoftware.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