Re: [lkp-robot] [x86/refcount] b631e535c6: WARNING:at_net/netlink/af_netlink.c:#netlink_sock_destruct

[Hans Liljestrand]

On Tue, Jul 25, 2017 at 11:38:30AM -0700, Kees Cook wrote:
> On Tue, Jul 25, 2017 at 3:43 AM, Hans Liljestrand
> <liljestrandh@xxxxxxxxx> wrote:
> > On Mon, Jul 24, 2017 at 08:21:16PM -0700, Kees Cook wrote:
> > > On Mon, Jul 24, 2017 at 6:03 AM, Hans Liljestrand
> > > <liljestrandh@xxxxxxxxx> wrote:
> > > > On Sun, Jul 23, 2017 at 08:52:53PM -0700, Kees Cook wrote:
> > > > > Is 14afee4b6092f ("net: convert sock.sk_wmem_alloc from atomic_t to
> > > > > refcount_t") correct? That looks like a statistics counter, not a
> > > > > refcounter? I can't quite tell, though...
> > > >
> > > >
> > > >
> > > > Hmm, yes, it looks a bit weird, but it is used in a refcount fashion
> > > > here:
> > > >
> > > > void sk_free(struct sock *sk)
> > > > {
> > > >         /*
> > > >          * We subtract one from sk_wmem_alloc and can know if
> > > >          * some packets are still in some tx queue.
> > > >          * If not null, sock_wfree() will call __sk_free(sk) later
> > > >          */
> > > >         if (refcount_dec_and_test(&sk->sk_wmem_alloc))
> > > >                 __sk_free(sk);
> > > > }
> > > >
> > > > http://elixir.free-electrons.com/linux/v4.13-rc1/source/net/core/sock.c#L1605
> > >
> > >
> > > Ah yeah, there it is. Hrmpf. Something is triggering WARNs, though...
> > > I wonder if this can get examined more closely?
> >
> >
> > I tried reproducing the error but I don't seem to know how to use lkp. Got
> > lots of permission denied errors and finally ran out of disk space (after
> > using up ~50GB).
> >
> > Maybe I did something wrong?
> >
> > What I did was: Cloned the related kernel repository, checked out offending
> > commit, plopped in config, compiled bzImage. Then I just cloned the lkp repo
> > and tried running the provided command line with the bzImage and provided
> > script.
> >
> > I'll take another look once I have the time, might be I missed something
> > earlier.
>
> Yeah, I'm not sure. Seems it was found through trinity? And only after
> 36 seconds, too.

I think I might have missed something here? I cannot find anything about 
trinity or 36 seconds? Although I either misplaced or didn't get the original 
email, so I'm not sure if it had some other attachments beyond the config and 
script?

> > > Also, why not atomic->refcount for sk_rmem_alloc?
> >
> > I couldn't find any similar refcount-like use on sk_rmem_alloc.
>
> Okay, interesting.
>
> > And as noted the sk_wmem_alloc thing is also a bit dubious. It looks like it
> > serves a dual purpose of actual allocation size and occasional reference
> > counter.
>
> Could you ask net-dev to see what is actually happening here? This
> looks like a regression, but also very odd (broken?) refcounting ...

Sure, but I'm unsure of what exactly I should be asking? If you have any more 
information on the trinity results I'd be happy to look at that beforehand?

Thanks,
-hans

> -Kees
>
>
> --
> Kees Cook
> Pixel Security