Re: [PATCH net v4 3/3] selftests/bpf: Add mptcp test with sockmap

[Matthieu Baerts <matttbe@kernel.org>]

Hi Jiayuan,

Thank you for this new test!

I'm not very familiar with the BPF selftests: it would be nice if
someone else can have a quick look.

On 05/11/2025 12:36, Jiayuan Chen wrote:
> Add test cases to verify that when MPTCP falls back to plain TCP sockets,
> they can properly work with sockmap.
> 
> Additionally, add test cases to ensure that sockmap correctly rejects
> MPTCP sockets as expected.
> 
> Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev>
> ---
>  .../testing/selftests/bpf/prog_tests/mptcp.c  | 150 ++++++++++++++++++
>  .../selftests/bpf/progs/mptcp_sockmap.c       |  43 +++++
>  2 files changed, 193 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/progs/mptcp_sockmap.c
> 
> diff --git a/tools/testing/selftests/bpf/prog_tests/mptcp.c b/tools/testing/selftests/bpf/prog_tests/mptcp.c
> index f8eb7f9d4fd2..56c556f603cc 100644
> --- a/tools/testing/selftests/bpf/prog_tests/mptcp.c
> +++ b/tools/testing/selftests/bpf/prog_tests/mptcp.c
> @@ -6,11 +6,14 @@
>  #include <netinet/in.h>
>  #include <test_progs.h>
>  #include <unistd.h>
> +#include <error.h>

Do you use this new include?

>  #include "cgroup_helpers.h"
>  #include "network_helpers.h"
> +#include "socket_helpers.h"
>  #include "mptcp_sock.skel.h"
>  #include "mptcpify.skel.h"
>  #include "mptcp_subflow.skel.h"
> +#include "mptcp_sockmap.skel.h"
>  
>  #define NS_TEST "mptcp_ns"
>  #define ADDR_1	"10.0.1.1"
> @@ -436,6 +439,151 @@ static void test_subflow(void)
>  	close(cgroup_fd);
>  }
>  
> +/* Test sockmap on MPTCP server handling non-mp-capable clients. */
> +static void test_sockmap_with_mptcp_fallback(struct mptcp_sockmap *skel)
> +{
> +	int listen_fd = -1, client_fd1 = -1, client_fd2 = -1;
> +	int server_fd1 = -1, server_fd2 = -1, sent, recvd;
> +	char snd[9] = "123456789";
> +	char rcv[10];
> +
> +	/* start server with MPTCP enabled */
> +	listen_fd = start_mptcp_server(AF_INET, NULL, 0, 0);
> +	if (!ASSERT_OK_FD(listen_fd, "redirect:start_mptcp_server"))
> +		return;
> +
> +	skel->bss->trace_port = ntohs(get_socket_local_port(listen_fd));
> +	skel->bss->sk_index = 0;
> +	/* create client without MPTCP enabled */
> +	client_fd1 = connect_to_fd_opts(listen_fd, NULL);
> +	if (!ASSERT_OK_FD(client_fd1, "redirect:connect_to_fd"))
> +		goto end;
> +
> +	server_fd1 = xaccept_nonblock(listen_fd, NULL, NULL);
> +	skel->bss->sk_index = 1;
> +	client_fd2 = connect_to_fd_opts(listen_fd, NULL);
> +	if (!ASSERT_OK_FD(client_fd2, "redirect:connect_to_fd"))
> +		goto end;
> +
> +	server_fd2 = xaccept_nonblock(listen_fd, NULL, NULL);
> +	/* test normal redirect behavior: data sent by client_fd1 can be
> +	 * received by client_fd2
> +	 */
> +	skel->bss->redirect_idx = 1;
> +	sent = xsend(client_fd1, snd, sizeof(snd), 0);
> +	if (!ASSERT_EQ(sent, sizeof(snd), "redirect:xsend(client_fd1)"))
> +		goto end;
> +
> +	/* try to recv more bytes to avoid truncation check */
> +	recvd = recv_timeout(client_fd2, rcv, sizeof(rcv), MSG_DONTWAIT, 2);
> +	if (!ASSERT_EQ(recvd, sizeof(snd), "redirect:recv(client_fd2)"))
> +		goto end;
> +
> +end:
> +	if (client_fd1 > 1)
> +		close(client_fd1);
> +	if (client_fd2 > 1)
> +		close(client_fd2);
> +	if (server_fd1 > 0)
> +		close(server_fd1);
> +	if (server_fd2 > 0)
> +		close(server_fd2);

Why do you check if it is above 0 or 1? Should you not always check if
it is >= 0 for each fd?


> +	close(listen_fd);
> +}
> +
> +/* Test sockmap rejection of MPTCP sockets - both server and client sides. */
> +static void test_sockmap_reject_mptcp(struct mptcp_sockmap *skel)
> +{
> +	int client_fd1 = -1, client_fd2 = -1;
> +	int listen_fd = -1, server_fd = -1;
> +	int err, zero = 0;
> +
> +	/* start server with MPTCP enabled */
> +	listen_fd = start_mptcp_server(AF_INET, NULL, 0, 0);
> +	if (!ASSERT_OK_FD(listen_fd, "start_mptcp_server"))

In test_sockmap_with_mptcp_fallback(), you prefixed each error with
'redirect:'. Should you also have a different prefix here? 'sockmap-fb:'
vs 'sockmap-mptcp:' eventually?

> +		return;
> +
> +	skel->bss->trace_port = ntohs(get_socket_local_port(listen_fd));
> +	skel->bss->sk_index = 0;
> +	/* create client with MPTCP enabled */
> +	client_fd1 = connect_to_fd(listen_fd, 0);
> +	if (!ASSERT_OK_FD(client_fd1, "connect_to_fd client_fd1"))
> +		goto end;
> +
> +	/* bpf_sock_map_update() called from sockops should reject MPTCP sk */
> +	if (!ASSERT_EQ(skel->bss->helper_ret, -EOPNOTSUPP, "should reject"))
> +		goto end;

So here, the client is connected, but sockmap doesn't operate on it,
right? So most likely, the connection is stalled until the userspace
realises that and takes an action?

> +	/* set trace_port = -1 to stop sockops */
> +	skel->bss->trace_port = -1;

What do you want to demonstrate from here? That without the sockmap
injection, there are no new entries added? Is it worth checking that here?

> +	client_fd2 = connect_to_fd(listen_fd, 0);
> +	if (!ASSERT_OK_FD(client_fd2, "connect_to_fd client_fd2"))
> +		goto end;
> +
> +	server_fd = xaccept_nonblock(listen_fd, NULL, NULL);
> +	err = bpf_map_update_elem(bpf_map__fd(skel->maps.sock_map),
> +				  &zero, &server_fd, BPF_NOEXIST);
> +	if (!ASSERT_EQ(err, -EOPNOTSUPP, "server should be disallowed"))
> +		goto end;
> +
> +	/* MPTCP client should also be disallowed */
> +	err = bpf_map_update_elem(bpf_map__fd(skel->maps.sock_map),
> +				  &zero, &client_fd1, BPF_NOEXIST);
> +	if (!ASSERT_EQ(err, -EOPNOTSUPP, "client should be disallowed"))
> +		goto end;
> +end:
> +	if (client_fd1 > 0)
> +		close(client_fd1);
> +	if (client_fd2 > 0)
> +		close(client_fd2);
> +	if (server_fd > 0)
> +		close(server_fd);

Same here: should it not be "*fd >= 0"?

> +	close(listen_fd);
> +}

(...)

Cheers,
Matt
-- 
Sponsored by the NGI0 Core fund.