On Wed, 28 May 2025, Max Staudt wrote:
Since the chardev is now created before the class device is registered, an attempt to tty_[k]open() the chardev between these two steps will lead to tty->dev being assigned NULL by alloc_tty_struct().
alloc_tty_struct() is called via tty_init_dev() when the tty is firstly opened, and is entered with tty_mutex held, so let's lock the critical section in tty_register_device_attr() with the same global mutex. This guarantees that tty->dev can be assigned a sane value.
Fixes: 6a7e6f78c235 ("tty: close race between device register and open") Signed-off-by: Max Staudt max@enpas.org Cc: stable@vger.kernel.org
drivers/tty/tty_io.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c index e922b84524d2..94768509e2d2 100644 --- a/drivers/tty/tty_io.c +++ b/drivers/tty/tty_io.c @@ -3258,6 +3258,8 @@ struct device *tty_register_device_attr(struct tty_driver *driver, else tty_line_name(driver, index, name);
- mutex_lock(&tty_mutex);
Use guard() so you don't need to change the returns and rollback path.
- if (!(driver->flags & TTY_DRIVER_DYNAMIC_ALLOC)) { /*
- Free any saved termios data so that the termios state is
@@ -3271,7 +3273,7 @@ struct device *tty_register_device_attr(struct tty_driver *driver, retval = tty_cdev_add(driver, devt, index, 1); if (retval)
return ERR_PTR(retval);
goto err_unlock;cdev_added = true; } @@ -3294,6 +3296,8 @@ struct device *tty_register_device_attr(struct tty_driver *driver, if (retval) goto err_put;
- mutex_unlock(&tty_mutex);
- return dev;
err_put: @@ -3309,6 +3313,9 @@ struct device *tty_register_device_attr(struct tty_driver *driver, driver->cdevs[index] = NULL; } +err_unlock:
- mutex_unlock(&tty_mutex);
- return ERR_PTR(retval);
} EXPORT_SYMBOL_GPL(tty_register_device_attr);