> On 8/23/20 12:13 AM, Dinghao Liu wrote:
> > When misc_register() fails, wd_data will be released by the
> > release callback function watchdog_core_data_release(), so
> > we don't need to free it again. But when watchdog_kworker is
> > NULL, we should free wd_data to prevent memleak.
> >
> > Fixes: cb36e29bb0e4b ("watchdog: initialize device before misc_register")
> > Signed-off-by: Dinghao Liu <dinghao.liu@xxxxxxxxxx>
> > ---
> > drivers/watchdog/watchdog_dev.c | 5 +++--
> > 1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
> > index 6798addabd5a..8ee78e26feb1 100644
> > --- a/drivers/watchdog/watchdog_dev.c
> > +++ b/drivers/watchdog/watchdog_dev.c
> > @@ -994,8 +994,10 @@ static int watchdog_cdev_register(struct watchdog_device *wdd)
> > wd_data->wdd = wdd;
> > wdd->wd_data = wd_data;
> >
> > - if (IS_ERR_OR_NULL(watchdog_kworker))
> > + if (IS_ERR_OR_NULL(watchdog_kworker)) {
> > + kfree(wd_data);
>
> This should be a separate patch, with
>
> Fixes: 664a39236e718 ("watchdog: Introduce hardware maximum heartbeat in watchdog core")
>
Thank you for your advice. I will send a new patch to fix this soon.
> > return -ENODEV;
> > + }
> >
> > device_initialize(&wd_data->dev);
> > wd_data->dev.devt = MKDEV(MAJOR(watchdog_devt), wdd->id);
> > @@ -1021,7 +1023,6 @@ static int watchdog_cdev_register(struct watchdog_device *wdd)
> > pr_err("%s: a legacy watchdog module is probably present.\n",
> > wdd->info->identity);
> > old_wd_data = NULL;
> > - kfree(wd_data);
>
> Are you sure about this ? put_device() isn't called on &wd_data->dev
> (unlike the code further below). How do you trigger the double free,
> or, in other words, how is watchdog_core_data_release() ever called
> in this code path ?
>
> device_initialize() says:
> NOTE: Use put_device() to give up your reference instead of freeing
> @dev directly once you have called this function.
> so it looks like put_device() should be called instead of kfree().
>
You are right. The callback will free wd_data->dev after all references
have gone away. So we should use put_device() here. I will fix this soon.
Regards,
Dinghao
