netdev - Re: [PATCHv2] net: bpf: reject invalid shifts

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Date:	Tue, 12 Jan 2016 15:28:22 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:	Daniel Borkmann <daniel@...earbox.net>,
	Rabin Vincent <rabin@....in>, davem@...emloft.net,
	netdev@...r.kernel.org, ast@...nel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCHv2] net: bpf: reject invalid shifts

On Tue, 2016-01-12 at 12:46 -0800, Alexei Starovoitov wrote:
> On Tue, Jan 12, 2016 at 09:42:39PM +0100, Daniel Borkmann wrote:

> > >yep and we all know who was able to code hundreds of cBPF insns by hand ;)
> > >But I'm sure that code doesn't have such broken shifts. :)))
> > 
> > libpcap certainly supports raw filters now thanks to Chema [1]. Alternative
> > could be to just mask them here, but not in eBPF verifier, but that would be
> > even more inconsistent (on the other hand, we also allow holes in BPF but not
> > in eBPF, so wouldn't be the first time we make things different), hmm.
> 
> I would rather see broken classic bpf program fixed instead of continue
> running them with undefined behavior.

This is your choice, because you are a developer.

Some people might be stuck with old software they can not update,
because they do not have the money to pay developers.

And no, I did not code BPF programs like that, but maybe others did, and
I feel the pain of customers that might be stuck.

Linus Torvalds always made clear we must provide backward compatibility,
and really this discussion should not even take place.

As I said, we used to load such BPF program in the past.

The fact that ARM64 crashes because of a faulty JIT implementation is
not an excuse.