selftests/bpf: Test [::] -> [::1] rewrite in sys_sendmsg in test_sock_addr

Test that sys_sendmsg BPF hook doesn't break sys_sendmsg behaviour to
rewrite destination IPv6 = [::] with [::1] (BSD'ism).

Two test cases are added:

1) User passes dst IPv6 = [::] and BPF_CGROUP_UDP6_SENDMSG program
   doesn't touch it.

2) User passes dst IPv6 != [::], but BPF_CGROUP_UDP6_SENDMSG program
   rewrites it with [::].

In both cases [::1] is used by sys_sendmsg code eventually and datagram
is sent successfully for unconnected UDP socket.

Example of relevant output:
  Test case: sendmsg6: set dst IP = [::] (BSD'ism) .. [PASS]
  Test case: sendmsg6: preserve dst IP = [::] (BSD'ism) .. [PASS]
Signed-off-by: Andrey Ignatov <rdna@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/testing/selftests/bpf/test_sock_addr.c

@@ -44,6 +44,7 @@
 #define SERV6_V4MAPPED_IP	"::ffff:192.168.0.4"
 #define SRC6_IP			"::1"
 #define SRC6_REWRITE_IP		"::6"
+#define WILDCARD6_IP		"::"
 #define SERV6_PORT		6060
 #define SERV6_REWRITE_PORT	6666
 
@@ -85,12 +86,14 @@ static int bind4_prog_load(const struct sock_addr_test *test);
 static int bind6_prog_load(const struct sock_addr_test *test);
 static int connect4_prog_load(const struct sock_addr_test *test);
 static int connect6_prog_load(const struct sock_addr_test *test);
+static int sendmsg_allow_prog_load(const struct sock_addr_test *test);
 static int sendmsg_deny_prog_load(const struct sock_addr_test *test);
 static int sendmsg4_rw_asm_prog_load(const struct sock_addr_test *test);
 static int sendmsg4_rw_c_prog_load(const struct sock_addr_test *test);
 static int sendmsg6_rw_asm_prog_load(const struct sock_addr_test *test);
 static int sendmsg6_rw_c_prog_load(const struct sock_addr_test *test);
 static int sendmsg6_rw_v4mapped_prog_load(const struct sock_addr_test *test);
+static int sendmsg6_rw_wildcard_prog_load(const struct sock_addr_test *test);
 
 static struct sock_addr_test tests[] = {
 	/* bind */
@@ -462,6 +465,34 @@ static struct sock_addr_test tests[] = {
 		SRC6_REWRITE_IP,
 		SYSCALL_ENOTSUPP,
 	},
+	{
+		"sendmsg6: set dst IP = [::] (BSD'ism)",
+		sendmsg6_rw_wildcard_prog_load,
+		BPF_CGROUP_UDP6_SENDMSG,
+		BPF_CGROUP_UDP6_SENDMSG,
+		AF_INET6,
+		SOCK_DGRAM,
+		SERV6_IP,
+		SERV6_PORT,
+		SERV6_REWRITE_IP,
+		SERV6_REWRITE_PORT,
+		SRC6_REWRITE_IP,
+		SUCCESS,
+	},
+	{
+		"sendmsg6: preserve dst IP = [::] (BSD'ism)",
+		sendmsg_allow_prog_load,
+		BPF_CGROUP_UDP6_SENDMSG,
+		BPF_CGROUP_UDP6_SENDMSG,
+		AF_INET6,
+		SOCK_DGRAM,
+		WILDCARD6_IP,
+		SERV6_PORT,
+		SERV6_REWRITE_IP,
+		SERV6_PORT,
+		SRC6_IP,
+		SUCCESS,
+	},
 	{
 		"sendmsg6: deny call",
 		sendmsg_deny_prog_load,
@@ -734,16 +765,27 @@ static int connect6_prog_load(const struct sock_addr_test *test)
 	return load_path(test, CONNECT6_PROG_PATH);
 }
 
-static int sendmsg_deny_prog_load(const struct sock_addr_test *test)
+static int sendmsg_ret_only_prog_load(const struct sock_addr_test *test,
+				      int32_t rc)
 {
 	struct bpf_insn insns[] = {
-		/* return 0 */
-		BPF_MOV64_IMM(BPF_REG_0, 0),
+		/* return rc */
+		BPF_MOV64_IMM(BPF_REG_0, rc),
 		BPF_EXIT_INSN(),
 	};
 	return load_insns(test, insns, sizeof(insns) / sizeof(struct bpf_insn));
 }
 
+static int sendmsg_allow_prog_load(const struct sock_addr_test *test)
+{
+	return sendmsg_ret_only_prog_load(test, /*rc*/ 1);
+}
+
+static int sendmsg_deny_prog_load(const struct sock_addr_test *test)
+{
+	return sendmsg_ret_only_prog_load(test, /*rc*/ 0);
+}
+
 static int sendmsg4_rw_asm_prog_load(const struct sock_addr_test *test)
 {
 	struct sockaddr_in dst4_rw_addr;
@@ -864,6 +906,11 @@ static int sendmsg6_rw_v4mapped_prog_load(const struct sock_addr_test *test)
 	return sendmsg6_rw_dst_asm_prog_load(test, SERV6_V4MAPPED_IP);
 }
 
+static int sendmsg6_rw_wildcard_prog_load(const struct sock_addr_test *test)
+{
+	return sendmsg6_rw_dst_asm_prog_load(test, WILDCARD6_IP);
+}
+
 static int sendmsg6_rw_c_prog_load(const struct sock_addr_test *test)
 {
 	return load_path(test, SENDMSG6_PROG_PATH);