Re: [v3] nbd: fix potential NULL pointer fault in nbd_genl_disconnect

[sunke (E)]

å 2020/2/11 1:05, Mike Christie åé:
> On 02/10/2020 01:32 AM, Sun Ke wrote:
> > Open /dev/nbdX first, the config_refs will be 1 and
> > the pointers in nbd_device are still null. Disconnect
> > /dev/nbdX, then reference a null recv_workq. The
> > protection by config_refs in nbd_genl_disconnect is useless.
> >
> > To fix it, just add a check for a non null task_recv in
> > nbd_genl_disconnect.
> >
> > Signed-off-by: Sun Ke <sunke32@xxxxxxxxxx>
> > ---
> > v1 -> v2:
> > Add an omitted mutex_unlock.
> >
> > v2 -> v3:
> > Add nbd->config_lock, suggested by Josef.
> > ---
> >   drivers/block/nbd.c | 8 ++++++++
> >   1 file changed, 8 insertions(+)
> >
> > diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
> > index b4607dd96185..870b3fd0c101 100644
> > --- a/drivers/block/nbd.c
> > +++ b/drivers/block/nbd.c
> > @@ -2008,12 +2008,20 @@ static int nbd_genl_disconnect(struct sk_buff *skb, struct genl_info *info)
> >   		       index);
> >   		return -EINVAL;
> >   	}
> > +	mutex_lock(&nbd->config_lock);
> >   	if (!refcount_inc_not_zero(&nbd->refs)) {
> > +		mutex_unlock(&nbd->config_lock);
> >   		mutex_unlock(&nbd_index_mutex);
> >   		printk(KERN_ERR "nbd: device at index %d is going down\n",
> >   		       index);
> >   		return -EINVAL;
> >   	}
> > +	if (!nbd->recv_workq) {
> > +		mutex_unlock(&nbd->config_lock);
> > +		mutex_unlock(&nbd_index_mutex);
> > +		return -EINVAL;
> > +	}
> > +	mutex_unlock(&nbd->config_lock);
> >   	mutex_unlock(&nbd_index_mutex);
> >   	if (!refcount_inc_not_zero(&nbd->config_refs)) {
> >   		nbd_put(nbd);
>
> With my other patch then we will not need this right? It handles your
> case by just being integrated with the existing checks in:
>
> nbd_disconnect_and_put->nbd_clear_sock->sock_shutdown
>
> ...
>
> static void sock_shutdown(struct nbd_device *nbd)
> {
>
> ....
>
>          if (config->num_connections == 0)
>                  return;
>
>
> num_connections is zero for your case since we never did a
> nbd_genl_disconnect so we would return here.
>
>
> .
Hi Mike

Your point is not right totally.

Yes, config->num_connections is 0 and will return in sock_shutdown. Then 
it will back to nbd_disconnect_and_put and do flush_workqueue 
(nbd->recv_workq).

nbd_disconnect_and_put
	->nbd_clear_sock
		->sock_shutdown
	->flush_workqueue

Thanks,
Sun Ke