netdev - Re: [PATCH bpf] selftests/bpf: fix v4_to_v6 in sk

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Date:   Mon, 10 Aug 2020 09:14:18 -0700
From:   Stanislav Fomichev <sdf@...gle.com>
To:     Jakub Sitnicki <jakub@...udflare.com>
Cc:     Netdev <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [PATCH bpf] selftests/bpf: fix v4_to_v6 in sk_lookup

On Sat, Aug 8, 2020 at 11:46 AM Jakub Sitnicki <jakub@...udflare.com> wrote:
>
> On Sat, Aug 08, 2020 at 12:38 AM CEST, Stanislav Fomichev wrote:
> > I'm getting some garbage in bytes 8 and 9 when doing conversion
> > from sockaddr_in to sockaddr_in6 (leftover from AF_INET?).
> > Let's explicitly clear the higher bytes.
> >
> > Signed-off-by: Stanislav Fomichev <sdf@...gle.com>
> > ---
> >  tools/testing/selftests/bpf/prog_tests/sk_lookup.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/tools/testing/selftests/bpf/prog_tests/sk_lookup.c b/tools/testing/selftests/bpf/prog_tests/sk_lookup.c
> > index c571584c00f5..9ff0412e1fd3 100644
> > --- a/tools/testing/selftests/bpf/prog_tests/sk_lookup.c
> > +++ b/tools/testing/selftests/bpf/prog_tests/sk_lookup.c
> > @@ -309,6 +309,7 @@ static void v4_to_v6(struct sockaddr_storage *ss)
> >       v6->sin6_addr.s6_addr[10] = 0xff;
> >       v6->sin6_addr.s6_addr[11] = 0xff;
> >       memcpy(&v6->sin6_addr.s6_addr[12], &v4.sin_addr.s_addr, 4);
> > +     memset(&v6->sin6_addr.s6_addr[0], 0, 10);
> >  }
> >
> >  static int udp_recv_send(int server_fd)
>
> That was badly written. Sorry about that. And thanks for the fix.
>
> I'd even zero out the whole thing:
>
>         memset(v6, 0, sizeof(*v6));
>
> ... because right now IPv4 address is left as sin6_flowinfo.  I can
> follow up with that change, unless you'd like to roll a v2.
Up to you, but I'm not sure zeroing out the whole v6 portion is the
best way forward.
IMO, it's a bit confusing when reading the code.
It will work, but only because v4 and v6 address portions don't really
overlap :-/
I was thinking about adding new, on the stack sin6, fully initializing
it and then doing memcpy into ss.
But I decided that adding memset is probably good enough :-)