From: Shmulik Ladkani <shmulik.ladkani@gmail.com>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>,
netdev <netdev@vger.kernel.org>,
Alexander Duyck <alexander.duyck@gmail.com>,
Alexei Starovoitov <ast@kernel.org>, Yonghong Song <yhs@fb.com>,
Steffen Klassert <steffen.klassert@secunet.com>,
shmulik@metanetworks.com, eyal@metanetworks.com
Subject: Re: BUG_ON in skb_segment, after bpf_skb_change_proto was applied
Date: Tue, 27 Aug 2019 14:42:18 +0300 [thread overview]
Message-ID: <20190827144218.5b098eac@pixies> (raw)
In-Reply-To: <94cd6f4d-09d4-11c0-64f4-bdc544bb3dcb@gmail.com>
On Mon, 26 Aug 2019 19:47:40 +0200
Eric Dumazet <eric.dumazet@gmail.com> wrote:
> On 8/26/19 4:07 PM, Shmulik Ladkani wrote:
> > - ipv4 forwarding to dummy1, where eBPF nat4-to-6 program is attached
> > at TC Egress (calls 'bpf_skb_change_proto()'), then redirect to ingress
> > on same device.
> > NOTE: 'bpf_skb_proto_4_to_6()' mangles 'shinfo->gso_size'
>
> Doing this on an skb with a frag_list is doomed, in current gso_segment() state.
>
> A rewrite would be needed (I believe I did so at some point, but Herbert Xu fought hard against it)
Thanks Eric,
- If a rewrite is still considered out of the question, how can one use
eBPF's bpf_skb_change_proto() safely without disabling GRO completely?
- e.g. is there a way to force the GROed skbs to fit into a layout that is
tolerated by skb_segment?
- alternatively can eBPF layer somehow enforce segmentation of the
original GROed skb before mangling the gso_size?
- Another thing that puzzles me is that we hit the BUG_ON rather rarely
and cannot yet reproduce synthetically. If skb_segment's handling of
skbs with a frag_list (that have gso_size mangled) is broken, I'd expect
to hit this more often... Any ideas?
- Suppose going for a rewrite, care to elaborate what's exactly missing
in skb_segment's logic?
I must admit I do not fully understand all the different code flows in
this function, it seems to support many different input skbs - any
assistance is highly appreciated.
Shmulik
next prev parent reply other threads:[~2019-08-27 11:42 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-26 14:07 BUG_ON in skb_segment, after bpf_skb_change_proto was applied Shmulik Ladkani
2019-08-26 17:47 ` Eric Dumazet
2019-08-27 11:42 ` Shmulik Ladkani [this message]
2019-08-27 12:10 ` Daniel Borkmann
2019-08-28 5:56 ` Shmulik Ladkani
2019-08-29 12:22 ` Shmulik Ladkani
2019-09-01 20:05 ` Willem de Bruijn
2019-09-02 13:44 ` Shmulik Ladkani
2019-09-03 15:51 ` Shmulik Ladkani
2019-09-03 16:23 ` Willem de Bruijn
2019-09-03 17:03 ` Shmulik Ladkani
2019-09-03 17:24 ` Willem de Bruijn
2019-08-27 15:09 ` Eric Dumazet
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