[PATCH 05/24] Bluetooth: Fix racy acquire of rfcomm_dev reference

Peter Hurley
2014-02-10T02:21:59Z

rfcomm_dev_get() can return a rfcomm_dev reference for a
device for which destruction may be commencing. This can happen
on tty destruction, which calls rfcomm_tty_cleanup(), the last
port reference may have been released but RFCOMM_TTY_RELEASED
was not set. The following race is also possible:

CPU 0 | CPU 1
| rfcomm_release_dev
rfcomm_dev_get | .
spin_lock | .
dev = __rfcomm_dev_get | .
if dev | .
if test_bit(TTY_RELEASED) | .
| !test_and_set_bit(TTY_RELEASED)
| tty_port_put <<<< last reference
else |
tty_port_get |

The reference acquire is bogus because destruction will commence
with the release of the last reference.

Ignore the external state change of TTY_RELEASED and instead rely
on the reference acquire itself to determine if the reference is
valid.

Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
---
net/bluetooth/rfcomm/tty.c | 8 ++------
1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/net/bluetooth/rfcomm/tty.c b/net/bluetooth/rfcomm/tty.c
index a535ef1..7cf193f 100644
--- a/net/bluetooth/rfcomm/tty.c
+++ b/net/bluetooth/rfcomm/tty.c
@@ -157,12 +157,8 @@ static struct rfcomm_dev *rfcomm_dev_get(int id)

dev = __rfcomm_dev_get(id);

- if (dev) {
- if (test_bit(RFCOMM_TTY_RELEASED, &dev->flags))
- dev = NULL;
- else
- tty_port_get(&dev->port);
- }
+ if (dev && !tty_port_get(&dev->port))
+ dev = NULL;

spin_unlock(&rfcomm_dev_lock);

--
1.8.1.2