From bhalevy@panasas.com Fri Jun 8 10:10:44 2007 From: Benny Halevy Date: Tue, 15 May 2007 11:15:27 +0300 Subject: USB: fix usb_serial_put synchronization Subject: synchronization in usb_serial_put To: gregkh@suse.de Cc: linux-kernel@vger.kernel.org Message-ID: <46496C1F.3090209@panasas.com> I think there is a race between usb_serial_put() and usb_serial_get_by_index() (and get_free_serial()) with regards to handling the serial port refcount. usb_serial_get_by_index() gets a reference on the serial port under table_lock while return_serial releases all the returned ports from the table under the same lock. However, the table_lock is not taken around the call to kref_put, theoretically allowing to sneak in and grab a reference after kref_put has already determined that the reference count is zero (and before calling destroy_serial) causing use after free. Signed-off-by: Benny Halevy Cc: Oliver Neukum Signed-off-by: Greg Kroah-Hartman --- drivers/usb/serial/usb-serial.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) --- a/drivers/usb/serial/usb-serial.c +++ b/drivers/usb/serial/usb-serial.c @@ -122,11 +122,9 @@ static void return_serial(struct usb_ser if (serial == NULL) return; - spin_lock(&table_lock); for (i = 0; i < serial->num_ports; ++i) { serial_table[serial->minor + i] = NULL; } - spin_unlock(&table_lock); } static void destroy_serial(struct kref *kref) @@ -174,7 +172,9 @@ static void destroy_serial(struct kref * void usb_serial_put(struct usb_serial *serial) { + spin_lock(&table_lock); kref_put(&serial->kref, destroy_serial); + spin_unlock(&table_lock); } /*****************************************************************************