Subject: Re: [PATCH bpf] selftests/bpf: fix v4_to_v6 in sk_lookup

From: Jakub Sitnicki <[email-masked]>
Date: Sat, 08 Aug 2020 20:46:20 +0200

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 <[email-masked]>
> ---
>  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.

Fixes: 0ab5539f8584 ("selftests/bpf: Tests for BPF_SK_LOOKUP attach point")
Reviewed-by: Jakub Sitnicki <[email-masked]>