bpf, sockmap: Add tests for MSG_F_PEEK

Test that we can read with MSG_F_PEEK and then still get correct number
of available bytes through FIONREAD. The recv() (without PEEK) then
returns the bytes as expected. The recv() always worked though because
it was just the available byte reporting that was broke before latest
fixes.

Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Jakub Sitnicki <jakub@cloudflare.com>
Link: https://lore.kernel.org/bpf/20230926035300.135096-4-john.fastabend@gmail.com

Author: jrfastab

tools/testing/selftests/bpf/prog_tests/sockmap_basic.c

@@ -475,6 +475,55 @@ static void test_sockmap_skb_verdict_fionread(bool pass_prog)
 		test_sockmap_drop_prog__destroy(drop);
 }
 
+static void test_sockmap_skb_verdict_peek(void)
+{
+	int err, map, verdict, s, c1, p1, zero = 0, sent, recvd, avail;
+	struct test_sockmap_pass_prog *pass;
+	char snd[256] = "0123456789";
+	char rcv[256] = "0";
+
+	pass = test_sockmap_pass_prog__open_and_load();
+	if (!ASSERT_OK_PTR(pass, "open_and_load"))
+		return;
+	verdict = bpf_program__fd(pass->progs.prog_skb_verdict);
+	map = bpf_map__fd(pass->maps.sock_map_rx);
+
+	err = bpf_prog_attach(verdict, map, BPF_SK_SKB_STREAM_VERDICT, 0);
+	if (!ASSERT_OK(err, "bpf_prog_attach"))
+		goto out;
+
+	s = socket_loopback(AF_INET, SOCK_STREAM);
+	if (!ASSERT_GT(s, -1, "socket_loopback(s)"))
+		goto out;
+
+	err = create_pair(s, AF_INET, SOCK_STREAM, &c1, &p1);
+	if (!ASSERT_OK(err, "create_pairs(s)"))
+		goto out;
+
+	err = bpf_map_update_elem(map, &zero, &c1, BPF_NOEXIST);
+	if (!ASSERT_OK(err, "bpf_map_update_elem(c1)"))
+		goto out_close;
+
+	sent = xsend(p1, snd, sizeof(snd), 0);
+	ASSERT_EQ(sent, sizeof(snd), "xsend(p1)");
+	recvd = recv(c1, rcv, sizeof(rcv), MSG_PEEK);
+	ASSERT_EQ(recvd, sizeof(rcv), "recv(c1)");
+	err = ioctl(c1, FIONREAD, &avail);
+	ASSERT_OK(err, "ioctl(FIONREAD) error");
+	ASSERT_EQ(avail, sizeof(snd), "after peek ioctl(FIONREAD)");
+	recvd = recv(c1, rcv, sizeof(rcv), 0);
+	ASSERT_EQ(recvd, sizeof(rcv), "recv(p0)");
+	err = ioctl(c1, FIONREAD, &avail);
+	ASSERT_OK(err, "ioctl(FIONREAD) error");
+	ASSERT_EQ(avail, 0, "after read ioctl(FIONREAD)");
+
+out_close:
+	close(c1);
+	close(p1);
+out:
+	test_sockmap_pass_prog__destroy(pass);
+}
+
 void test_sockmap_basic(void)
 {
 	if (test__start_subtest("sockmap create_update_free"))
@@ -515,4 +564,6 @@ void test_sockmap_basic(void)
 		test_sockmap_skb_verdict_fionread(true);
 	if (test__start_subtest("sockmap skb_verdict fionread on drop"))
 		test_sockmap_skb_verdict_fionread(false);
+	if (test__start_subtest("sockmap skb_verdict msg_f_peek"))
+		test_sockmap_skb_verdict_peek();
 }