Re: [Patch] mqueue: fix netlink sock refcnt and skb refcnt

From: Cong Wang
Date: Mon Jul 10 2017 - 13:20:11 EST

On Sun, Jul 9, 2017 at 10:08 PM, Cong Wang <xiyou.wangcong@xxxxxxxxx> wrote:
> netlink_sendskb() is problematic, it releases sock refcnt
> silently which could cause troubles we can call it multiple
> times. info->notify_sock is a good example where we
> setup once and use it to send netlink skb's for many times.
> It should not hold or release any refcnt, but needs to rely
> on netlink_attachskb()/netlink_detachskb() to hold/release
> the corresponding refcnt.
> Same for the skb attached to this sock, it is allocated once
> and used for multiple times, so we should hold its refcnt
> in netlink_attachskb().
> At last, we need to call netlink_detachskb() to release
> both refcnt's after we remove the notification.

Hmm, the info->notify_owner is NULL'ed after sending
the notification, so probably we don't put the sock refcnt
repeatly. Not sure about the skb though...