[Openvpn-devel,v2] Implement constructing a control channel reset client as standalone fucntion

diff --git a/src/openvpn/packet_id.h b/src/openvpn/packet_id.h
index 410071e26..e5ffd485c 100644
--- a/src/openvpn/packet_id.h
+++ b/src/openvpn/packet_id.h
@@ -289,6 +289,21 @@  packet_id_persist_save_obj(struct packet_id_persist *p, const struct packet_id *
     }
 }
 
+/**
+ * Reset the current send packet id to its initial state.
+ * Use very carefully only as (e.g. in the standalone reset packet context)
+ * to avoid sending more than one packet with the same packet id (that is not
+ * also a resend like the reset packet)
+ *
+ * @param p the packet structure to modify
+ */
+static inline void
+reset_packet_id_send(struct packet_id_send *p)
+{
+    p->time = 0;
+    p->id = 0;
+}
+
 const char *packet_id_net_print(const struct packet_id_net *pin, bool print_timestamp, struct gc_arena *gc);
 
 static inline int
diff --git a/src/openvpn/ssl.h b/src/openvpn/ssl.h
index ddf70422a..e925a16ea 100644
--- a/src/openvpn/ssl.h
+++ b/src/openvpn/ssl.h
@@ -53,12 +53,6 @@ 
  */
 #define CONTROL_SEND_ACK_MAX 4
 
-/*
- * Define number of buffers for send and receive in the reliability layer.
- */
-#define TLS_RELIABLE_N_SEND_BUFFERS  4 /* also window size for reliability layer */
-#define TLS_RELIABLE_N_REC_BUFFERS   8
-
 /*
  * Various timeouts
  */
diff --git a/src/openvpn/ssl_pkt.c b/src/openvpn/ssl_pkt.c
index 7233871b1..a93027505 100644
--- a/src/openvpn/ssl_pkt.c
+++ b/src/openvpn/ssl_pkt.c
@@ -398,3 +398,35 @@  error:
     gc_free(&gc);
     return VERDICT_INVALID;
 }
+
+struct buffer
+tls_reset_standalone(struct tls_auth_standalone *tas,
+                     struct session_id *own_sid,
+                     struct session_id *remote_sid,
+                     uint8_t header)
+{
+    struct buffer buf = alloc_buf(tas->frame.buf.payload_size);
+    ASSERT(buf_init(&buf, tas->frame.buf.headroom));
+
+    /* Reliable ACK structure */
+    /* Length of the ACK structure - 1 ACK */
+    buf_write_u8(&buf, 1);
+
+    /* ACKed packet - first packet's id is always 0 */
+    buf_write_u32(&buf, 0);
+
+    /* Remote session id */
+    buf_write(&buf, remote_sid->id, SID_SIZE);
+
+    /* Packet ID of our own packet: Our reset packet is always using
+     * packet id 0 since it is the first packet */
+    packet_id_type net_pid = htonpid(0);
+
+    ASSERT(buf_write(&buf, &net_pid, sizeof(net_pid)));
+
+    /* Add tls-auth/tls-crypt wrapping, this might replace buf */
+    tls_wrap_control(&tas->tls_wrap, header, &buf, own_sid);
+
+    return buf;
+}
+
diff --git a/src/openvpn/ssl_pkt.h b/src/openvpn/ssl_pkt.h
index b7a8d9c35..dd9361407 100644
--- a/src/openvpn/ssl_pkt.h
+++ b/src/openvpn/ssl_pkt.h
@@ -60,6 +60,12 @@ 
 #define P_FIRST_OPCODE                 3
 #define P_LAST_OPCODE                  10
 
+/*
+ * Define number of buffers for send and receive in the reliability layer.
+ */
+#define TLS_RELIABLE_N_SEND_BUFFERS  4 /* also window size for reliability layer */
+#define TLS_RELIABLE_N_REC_BUFFERS   8
+
 /*
  * Used in --mode server mode to check tls-auth signature on initial
  * packets received from new clients.
@@ -157,6 +163,19 @@  read_control_auth(struct buffer *buf,
                   const struct link_socket_actual *from,
                   const struct tls_options *opt);
 
+
+/**
+ * This function creates a reset packet using the information
+ * from the tls pre decrypt state.
+ *
+ * The returned buf need to be free with \c free_buf
+ */
+struct buffer
+tls_reset_standalone(struct tls_auth_standalone *tas,
+                     struct session_id *own_sid,
+                     struct session_id *remote_sid,
+                     uint8_t header);
+
 static inline const char *
 packet_opcode_name(int op)
 {
diff --git a/tests/unit_tests/openvpn/test_pkt.c b/tests/unit_tests/openvpn/test_pkt.c
index 022e15d3e..77338cd3a 100644
--- a/tests/unit_tests/openvpn/test_pkt.c
+++ b/tests/unit_tests/openvpn/test_pkt.c
@@ -87,25 +87,25 @@  const char static_key[] = "<tls-auth>\n"
                           "</tls-auth>\n";
 
 const uint8_t client_reset_v2_none[] =
-    { 0x38, 0x68, 0x91, 0x92,  0x3f, 0xa3, 0x10, 0x34,
-      0x37, 0x00, 0x00, 0x00, 0x00, 0x00 };
+{ 0x38, 0x68, 0x91, 0x92,  0x3f, 0xa3, 0x10, 0x34,
+  0x37, 0x00, 0x00, 0x00, 0x00, 0x00 };
 
 const uint8_t client_reset_v2_tls_auth[] =
-    { 0x38, 0xde, 0x69, 0x4c, 0x5c, 0x7b, 0xfb, 0xa2,
-      0x74, 0x93, 0x53, 0x7c, 0x1d, 0xed, 0x4e, 0x78,
-     0x15, 0x29, 0xae, 0x7c, 0xfe, 0x4b, 0x8c, 0x6d,
-     0x6b, 0x2b, 0x51, 0xf0, 0x5a, 0x00, 0x00, 0x00,
-     0x01, 0x61, 0xd3, 0xbf, 0x6c, 0x00, 0x00, 0x00,
-     0x00, 0x00};
+{ 0x38, 0xde, 0x69, 0x4c, 0x5c, 0x7b, 0xfb, 0xa2,
+  0x74, 0x93, 0x53, 0x7c, 0x1d, 0xed, 0x4e, 0x78,
+  0x15, 0x29, 0xae, 0x7c, 0xfe, 0x4b, 0x8c, 0x6d,
+  0x6b, 0x2b, 0x51, 0xf0, 0x5a, 0x00, 0x00, 0x00,
+  0x01, 0x61, 0xd3, 0xbf, 0x6c, 0x00, 0x00, 0x00,
+  0x00, 0x00};
 
 const uint8_t client_reset_v2_tls_crypt[] =
-    {0x38, 0xf4, 0x19, 0xcb, 0x12, 0xd1, 0xf9, 0xe4,
-     0x8f, 0x00, 0x00, 0x00, 0x01, 0x61, 0xd3, 0xf8,
-     0xe1, 0x33, 0x02, 0x06, 0xf5, 0x68, 0x02, 0xbe,
-     0x44, 0xfb, 0xed, 0x90, 0x50, 0x64, 0xe3, 0xdb,
-     0x43, 0x41, 0x6b, 0xec, 0x5e, 0x52, 0x67, 0x19,
-     0x46, 0x2b, 0x7e, 0xb9, 0x0c, 0x96, 0xde, 0xfc,
-     0x9b, 0x05, 0xc4, 0x48, 0x79, 0xf7};
+{0x38, 0xf4, 0x19, 0xcb, 0x12, 0xd1, 0xf9, 0xe4,
+ 0x8f, 0x00, 0x00, 0x00, 0x01, 0x61, 0xd3, 0xf8,
+ 0xe1, 0x33, 0x02, 0x06, 0xf5, 0x68, 0x02, 0xbe,
+ 0x44, 0xfb, 0xed, 0x90, 0x50, 0x64, 0xe3, 0xdb,
+ 0x43, 0x41, 0x6b, 0xec, 0x5e, 0x52, 0x67, 0x19,
+ 0x46, 0x2b, 0x7e, 0xb9, 0x0c, 0x96, 0xde, 0xfc,
+ 0x9b, 0x05, 0xc4, 0x48, 0x79, 0xf7};
 
 /* Valid tls-auth client CONTROL_V1 packet with random server id */
 const uint8_t client_ack_tls_auth_randomid[] = {
@@ -148,15 +148,19 @@  const uint8_t client_ack_tls_auth_randomid[] = {
     0xdb, 0x56, 0xf6, 0x40, 0xd1, 0xed, 0xdb, 0x91,
     0x81, 0xd6, 0xef, 0x83, 0x86, 0x8a, 0xb2, 0x3d,
     0x88, 0x92, 0x3f, 0xd8, 0x51, 0x9c, 0xd6, 0x26,
-    0x56, 0x33, 0x6b};
+    0x56, 0x33, 0x6b
+};
 
-struct tls_auth_standalone init_tas_auth(int key_direction)
+struct tls_auth_standalone
+init_tas_auth(int key_direction)
 {
     struct tls_auth_standalone tas = { 0 };
+    struct frame frame = { {.headroom = 200, .payload_size = 1400}, 0};
+    tas.frame = frame;
 
     tas.tls_wrap.mode = TLS_WRAP_AUTH;
     /* we ignore packet ids on for the first packet check */
-    tas.tls_wrap.opt.flags |= CO_IGNORE_PACKET_ID;
+    tas.tls_wrap.opt.flags |= (CO_IGNORE_PACKET_ID|CO_PACKET_ID_LONG_FORM);
 
     struct key_type tls_crypt_kt;
     init_key_type(&tls_crypt_kt, "none", "SHA1", true, false);
@@ -167,11 +171,12 @@  struct tls_auth_standalone init_tas_auth(int key_direction)
     return tas;
 }
 
-struct tls_auth_standalone init_tas_crypt(bool server)
+struct tls_auth_standalone
+init_tas_crypt(bool server)
 {
     struct tls_auth_standalone tas = { 0 };
     tas.tls_wrap.mode = TLS_WRAP_CRYPT;
-    tas.tls_wrap.opt.flags |= CO_IGNORE_PACKET_ID;
+    tas.tls_wrap.opt.flags |= (CO_IGNORE_PACKET_ID|CO_PACKET_ID_LONG_FORM);
 
     tls_crypt_init_key(&tas.tls_wrap.opt.key_ctx_bi, static_key, true, server);
 
@@ -209,7 +214,7 @@  test_tls_decrypt_lite_crypt(void **ut_state)
     free_tls_pre_decrypt_state(&state);
 
     /* flip a byte in various places */
-    for (int i=0;i<sizeof(client_reset_v2_tls_crypt);i++)
+    for (int i = 0; i<sizeof(client_reset_v2_tls_crypt); i++)
     {
         buf_reset_len(&buf);
         buf_write(&buf, client_reset_v2_tls_crypt, sizeof(client_reset_v2_tls_crypt));
@@ -324,6 +329,84 @@  test_tls_decrypt_lite_none(void **ut_state)
     free_buf(&buf);
 }
 
+static void
+test_generate_reset_packet_plain(void **ut_state)
+{
+    struct link_socket_actual from = { 0 };
+    struct tls_auth_standalone tas = { 0 };
+    struct tls_pre_decrypt_state state = { 0 };
+
+    struct session_id client_id = {{0, 1, 2, 3, 4, 5, 6, 7}};
+    struct session_id server_id = {{8, 9, 0, 9, 8, 7, 6, 2}};
+
+    enum first_packet_verdict verdict;
+
+    tas.tls_wrap.mode = TLS_WRAP_NONE;
+    struct frame frame = { {.headroom = 200, .payload_size = 1400}, 0};
+    tas.frame = frame;
+
+    uint8_t header = 0 | (P_CONTROL_HARD_RESET_CLIENT_V2 << P_OPCODE_SHIFT);
+
+    struct buffer buf = tls_reset_standalone(&tas, &client_id, &server_id, header);
+
+
+    verdict = tls_pre_decrypt_lite(&tas, &state, &from, &buf);
+    assert_int_equal(verdict, VERDICT_VALID_RESET);
+
+    /* Assure repeated generation of reset is deterministic/stateless*/
+    assert_memory_equal(state.peer_session_id.id, client_id.id, SID_SIZE);
+    struct buffer buf2 = tls_reset_standalone(&tas, &client_id, &server_id, header);
+    assert_int_equal(BLEN(&buf), BLEN(&buf2));
+    assert_memory_equal(BPTR(&buf), BPTR(&buf2), BLEN(&buf));
+    free_buf(&buf2);
+
+    free_tls_pre_decrypt_state(&state);
+    free_buf(&buf);
+}
+
+static void
+test_generate_reset_packet_tls_auth(void **ut_state)
+{
+    struct link_socket_actual from = { 0 };
+    struct tls_pre_decrypt_state state = { 0 };
+
+    struct tls_auth_standalone tas_server = init_tas_auth(KEY_DIRECTION_NORMAL);
+    struct tls_auth_standalone tas_client = init_tas_auth(KEY_DIRECTION_INVERSE);
+
+    packet_id_init(&tas_client.tls_wrap.opt.packet_id, 5, 5, "UNITTEST", 0);
+
+    struct session_id client_id = {{0xab, 1, 2, 3, 4, 5, 6, 0xcd}};
+    struct session_id server_id = {{8, 9, 0xa, 0xc, 8, 7, 6, 2}};
+
+    uint8_t header = 0 | (P_CONTROL_HARD_RESET_CLIENT_V2 << P_OPCODE_SHIFT);
+
+    now = 0x22446688;
+    reset_packet_id_send(&tas_client.tls_wrap.opt.packet_id.send);
+    struct buffer buf = tls_reset_standalone(&tas_client, &client_id, &server_id, header);
+
+    enum first_packet_verdict verdict = tls_pre_decrypt_lite(&tas_server, &state, &from, &buf);
+    assert_int_equal(verdict, VERDICT_VALID_RESET);
+
+    assert_memory_equal(state.peer_session_id.id, client_id.id, SID_SIZE);
+
+    /* Assure repeated generation of reset is deterministic/stateless*/
+    reset_packet_id_send(&tas_client.tls_wrap.opt.packet_id.send);
+    struct buffer buf2 = tls_reset_standalone(&tas_client, &client_id, &server_id, header);
+    assert_int_equal(BLEN(&buf), BLEN(&buf2));
+    assert_memory_equal(BPTR(&buf), BPTR(&buf2), BLEN(&buf));
+    free_buf(&buf2);
+
+
+    free_tls_pre_decrypt_state(&state);
+
+    packet_id_free(&tas_client.tls_wrap.opt.packet_id);
+
+    free_buf(&buf);
+    free_key_ctx_bi(&tas_server.tls_wrap.opt.key_ctx_bi);
+    free_key_ctx_bi(&tas_client.tls_wrap.opt.key_ctx_bi);
+
+}
+
 int
 main(void)
 {
@@ -331,6 +414,8 @@  main(void)
         cmocka_unit_test(test_tls_decrypt_lite_none),
         cmocka_unit_test(test_tls_decrypt_lite_auth),
         cmocka_unit_test(test_tls_decrypt_lite_crypt),
+        cmocka_unit_test(test_generate_reset_packet_plain),
+        cmocka_unit_test(test_generate_reset_packet_tls_auth),
     };
 
 #if defined(ENABLE_CRYPTO_OPENSSL)