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

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

[Stanislav Fomichev]

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@google.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)
-- 
2.28.0.236.gb10cc79966-goog

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

[Jakub Sitnicki]

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@google.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.

Fixes: 0ab5539f8584 ("selftests/bpf: Tests for BPF_SK_LOOKUP attach point")
Reviewed-by: Jakub Sitnicki <jakub@cloudflare.com>

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

[Stanislav Fomichev]

On Sat, Aug 8, 2020 at 11:46 AM Jakub Sitnicki <jakub@cloudflare.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@google.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 :-)

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

[Jakub Sitnicki]

On Mon, Aug 10, 2020 at 06:14 PM CEST, Stanislav Fomichev wrote:
> On Sat, Aug 8, 2020 at 11:46 AM Jakub Sitnicki <jakub@cloudflare.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@google.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 :-/

It's not that hacky :-) We copy sockaddr_in bits before overwriting ss:

	struct sockaddr_in v4 = *(struct sockaddr_in *)ss;

It could be easier to read, perhaps by copying just the fields we need:

	struct sockaddr_in *v4 = (struct sockaddr_in *)ss;
	uint32_t addr = v4->sin_addr.saddr;
	in_port_t port = v4->sin_port;

> 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 :-)

Makes sense. Either way sounds good to me.

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

[Daniel Borkmann]

On 8/8/20 12:38 AM, 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@google.com>

Applied, thanks!