netdev - Re: [PATCH bpf] bpf: lwtunnel: fix reroute supplying invalid dst

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Message-ID: <CAFTs51WM7yC3Z2HDGy9APSgqy1LCczQtFVG_y+X0WdxY9WSd9Q@mail.gmail.com>
Date:   Mon, 14 Oct 2019 10:39:06 -0700
From:   Peter Oskolkov <posk@...k.io>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Jiri Benc <jbenc@...hat.com>, bpf <bpf@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        Peter Oskolkov <posk@...gle.com>,
        Stanislav Fomichev <sdf@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH bpf] bpf: lwtunnel: fix reroute supplying invalid dst

On Sat, Oct 12, 2019 at 9:59 AM Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
>
> On Wed, Oct 9, 2019 at 1:31 AM Jiri Benc <jbenc@...hat.com> wrote:
> >
> > The dst in bpf_input() has lwtstate field set. As it is of the
> > LWTUNNEL_ENCAP_BPF type, lwtstate->data is struct bpf_lwt. When the bpf
> > program returns BPF_LWT_REROUTE, ip_route_input_noref is directly called on
> > this skb. This causes invalid memory access, as ip_route_input_slow calls
> > skb_tunnel_info(skb) that expects the dst->lwstate->data to be
> > struct ip_tunnel_info. This results to struct bpf_lwt being accessed as
> > struct ip_tunnel_info.
> >
> > Drop the dst before calling the IP route input functions (both for IPv4 and
> > IPv6).
> >
> > Reported by KASAN.
> >
> > Fixes: 3bd0b15281af ("bpf: add handling of BPF_LWT_REROUTE to lwt_bpf.c")
> > Cc: Peter Oskolkov <posk@...gle.com>
> > Signed-off-by: Jiri Benc <jbenc@...hat.com>
>
> Peter and other google folks,
> please review.

selftests/bpf/test_lwt_ip_encap.sh passes. Seems OK.

Acked-by: Peter Oskolkov <posk@...gle.com>