selftests/bpf: Add sockmap test for redirecting partial skb data

Add a test case to check whether sockmap redirection works correctly
when data length returned by stream_parser is less than skb->len.

In addition, this test checks whether strp_done is called correctly.
The reason is that we returns skb->len - 1 from the stream_parser, so
the last byte in the skb will be held by strp->skb_head. Therefore,
if strp_done is not called to free strp->skb_head, we'll get a memleak
warning.

Signed-off-by: Xu Kuohai <xukuohai@huawei.com>
Link: https://lore.kernel.org/r/20230804073740.194770-5-xukuohai@huaweicloud.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>

Author: Xu Kuohai

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

@@ -869,6 +869,77 @@ static void test_msg_redir_to_listening(struct test_sockmap_listen *skel,
 	xbpf_prog_detach2(verdict, sock_map, BPF_SK_MSG_VERDICT);
 }
 
+static void redir_partial(int family, int sotype, int sock_map, int parser_map)
+{
+	int s, c0, c1, p0, p1;
+	int err, n, key, value;
+	char buf[] = "abc";
+
+	key = 0;
+	value = sizeof(buf) - 1;
+	err = xbpf_map_update_elem(parser_map, &key, &value, 0);
+	if (err)
+		return;
+
+	s = socket_loopback(family, sotype | SOCK_NONBLOCK);
+	if (s < 0)
+		goto clean_parser_map;
+
+	err = create_socket_pairs(s, family, sotype, &c0, &c1, &p0, &p1);
+	if (err)
+		goto close_srv;
+
+	err = add_to_sockmap(sock_map, p0, p1);
+	if (err)
+		goto close;
+
+	n = xsend(c1, buf, sizeof(buf), 0);
+	if (n < sizeof(buf))
+		FAIL("incomplete write");
+
+	n = xrecv_nonblock(c0, buf, sizeof(buf), 0);
+	if (n != sizeof(buf) - 1)
+		FAIL("expect %zu, received %d", sizeof(buf) - 1, n);
+
+close:
+	xclose(c0);
+	xclose(p0);
+	xclose(c1);
+	xclose(p1);
+close_srv:
+	xclose(s);
+
+clean_parser_map:
+	key = 0;
+	value = 0;
+	xbpf_map_update_elem(parser_map, &key, &value, 0);
+}
+
+static void test_skb_redir_partial(struct test_sockmap_listen *skel,
+				   struct bpf_map *inner_map, int family,
+				   int sotype)
+{
+	int verdict = bpf_program__fd(skel->progs.prog_stream_verdict);
+	int parser = bpf_program__fd(skel->progs.prog_stream_parser);
+	int parser_map = bpf_map__fd(skel->maps.parser_map);
+	int sock_map = bpf_map__fd(inner_map);
+	int err;
+
+	err = xbpf_prog_attach(parser, sock_map, BPF_SK_SKB_STREAM_PARSER, 0);
+	if (err)
+		return;
+
+	err = xbpf_prog_attach(verdict, sock_map, BPF_SK_SKB_STREAM_VERDICT, 0);
+	if (err)
+		goto detach;
+
+	redir_partial(family, sotype, sock_map, parser_map);
+
+	xbpf_prog_detach2(verdict, sock_map, BPF_SK_SKB_STREAM_VERDICT);
+detach:
+	xbpf_prog_detach2(parser, sock_map, BPF_SK_SKB_STREAM_PARSER);
+}
+
 static void test_reuseport_select_listening(int family, int sotype,
 					    int sock_map, int verd_map,
 					    int reuseport_prog)
@@ -1243,6 +1314,7 @@ static void test_redir(struct test_sockmap_listen *skel, struct bpf_map *map,
 	} tests[] = {
 		TEST(test_skb_redir_to_connected),
 		TEST(test_skb_redir_to_listening),
+		TEST(test_skb_redir_partial),
 		TEST(test_msg_redir_to_connected),
 		TEST(test_msg_redir_to_listening),
 	};

tools/testing/selftests/bpf/progs/test_sockmap_listen.c

@@ -28,12 +28,26 @@ struct {
 	__type(value, unsigned int);
 } verdict_map SEC(".maps");
 
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(max_entries, 1);
+	__type(key, int);
+	__type(value, int);
+} parser_map SEC(".maps");
+
 bool test_sockmap = false; /* toggled by user-space */
 bool test_ingress = false; /* toggled by user-space */
 
 SEC("sk_skb/stream_parser")
 int prog_stream_parser(struct __sk_buff *skb)
 {
+	int *value;
+	__u32 key = 0;
+
+	value = bpf_map_lookup_elem(&parser_map, &key);
+	if (value && *value)
+		return *value;
+
 	return skb->len;
 }