Re: netlink: GPF in sock_sndtimeo

On Mon, Dec 12, 2016 at 2:02 AM, Richard Guy Briggs <rgb(a)redhat.com&gt; wrote: > On 2016-12-09 20:13, Cong Wang wrote: >> Netlink notifier can safely be converted to blocking one, I will send >> a patch. > > I had a quick look at how that might happen. The netlink notifier chain > is atomic. Would the registered callback funciton need to spawn a > one-time thread to avoid blocking? It is already non-atomic now: https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?i...

> I had a look at your patch. It looks attractively simple. The audit > next tree has patches queued that add an audit_reset function that will > require more work. I still see some potential gaps. > > - If the process messes up (or the sock lookup messes up) it is reset > in the kauditd thread under the audit_cmd_mutex. > > - If the process exits normally or is replaced due to an audit_replace > error, it is reset from audit_receive_skb under the audit_cmd_mutex. > > - If the process dies before the kauditd thread notices, either reap it > via notifier callback or it needs a check on net exit to reset. This > last one appears necessary to decrement the sock refcount so the sock > can be released in netlink_kernel_release(). > > If we want to be proactive and use the netlink notifier, we assume the > overhead of adding to the netlink notifier chain and eliminate all the > other reset calls under the kauditd thread. If we are ok being > reactionary, then we'll at least need the net exit check on audit_sock. I don't see why we need to check it in net exit if we use refcnt, because we have two different users of audit_sock: kauditd and netns, if both take care of refcnt properly, we don't need to worry about who is the last, no matter what failures occur in what order.