Re: [PATCH v4 2/3] Do error handling if __build_packet_message fails

[Florian Westphal <fw@strlen.de>]

Pablo Neira Ayuso <pablo@netfilter.org> wrote:
> On Tue, Nov 04, 2014 at 08:11:20PM +0100, Florian Westphal wrote:
> > Pablo Neira Ayuso <pablo@netfilter.org> wrote:
> > > BTW, we should also signal the userspace when we fail to build the
> > > message via:
> > > 
> > > nfnetlink_set_err(net, 0, group, -ENOBUFS);
> > > 
> > > so it knows that we're losing log messages for whatever reason.
> > > Basically, userspace hits -ENOBUFS when calling recv(), which means
> > > netlink is losing messages. I don't think we really need the
> > > statistics.
> > 
> > Not sure if this is a good idea.
> > 
> > a) __build_packet_message must never fail.
> > If it does, the kernel has a size accoutning bug somewhere.
> > b) I see no meaningful way for userspace to handle this error;
> > there is nothing it can do about it.
> > c) If it happens, it might be that some userspace logging daemon
> > suddently dies because it sees an unexpected 'fatal' error.
> 
> userspace should be handling -ENOBUFS already, netlink reports this if
> the buffer overruns.

You're right.

> I would remove those printk there to
> report OOM, there's nothing userspace can do with that.

Agreed.