netdev - Re: [PATCH net] bpf: Don't redirect too small packets

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Message-ID: <CAADnVQJy+0=6ZuAz-7dwOPK3sN2QrPiAcxhtojh8p65j0TRNhg@mail.gmail.com>
Date: Fri, 22 Mar 2024 20:01:51 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: patchwork-bot+netdevbpf@...nel.org
Cc: Eric Dumazet <edumazet@...gle.com>, "David S. Miller" <davem@...emloft.net>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Daniel Borkmann <daniel@...earbox.net>, Alexei Starovoitov <ast@...nel.org>, 
	Martin KaFai Lau <martin.lau@...ux.dev>, Andrii Nakryiko <andrii@...nel.org>, 
	Network Development <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>, 
	Eric Dumazet <eric.dumazet@...il.com>, 
	syzbot+9e27778c0edc62cb97d8@...kaller.appspotmail.com, 
	Stanislav Fomichev <sdf@...gle.com>, Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net] bpf: Don't redirect too small packets

On Fri, Mar 22, 2024 at 7:10 AM <patchwork-bot+netdevbpf@...nel.org> wrote:
>
> Hello:
>
> This patch was applied to bpf/bpf.git (master)
> by Daniel Borkmann <daniel@...earbox.net>:
>
> On Fri, 22 Mar 2024 12:24:07 +0000 you wrote:
> > Some drivers ndo_start_xmit() expect a minimal size, as shown
> > by various syzbot reports [1].
> >
> > Willem added in commit 217e6fa24ce2 ("net: introduce device min_header_len")
> > the missing attribute that can be used by upper layers.
> >
> > We need to use it in __bpf_redirect_common().

This patch broke empty_skb test:
$ test_progs -t empty_skb

test_empty_skb:FAIL:ret: veth ETH_HLEN+1 packet ingress
[redirect_ingress] unexpected ret: veth ETH_HLEN+1 packet ingress
[redirect_ingress]: actual -34 != expected 0
test_empty_skb:PASS:err: veth ETH_HLEN+1 packet ingress [redirect_egress] 0 nsec
test_empty_skb:FAIL:ret: veth ETH_HLEN+1 packet ingress
[redirect_egress] unexpected ret: veth ETH_HLEN+1 packet ingress
[redirect_egress]: actual -34 != expected 1

And looking at the test I think it's not a test issue.
This check
if (unlikely(skb->len < dev->min_header_len))
is rejecting more than it should.

So I reverted this patch for now.