Use WPACKET in dtls1_do_write()

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from openssl#24426)

ssl/statem/statem_dtls.c

@@ -96,6 +96,29 @@ void dtls1_hm_fragment_free(hm_fragment *frag)
     OPENSSL_free(frag);
 }
 
+static int dtls1_write_hm_header(unsigned char *msgheaderstart,
+                                 unsigned char msg_type, size_t msg_len,
+                                 unsigned short msg_seq, size_t fragoff,
+                                 size_t fraglen)
+{
+    WPACKET msgheader;
+    size_t msgheaderlen;
+
+    if (!WPACKET_init_static_len(&msgheader, msgheaderstart,
+                                 DTLS1_HM_HEADER_LENGTH, 0)
+        || !WPACKET_put_bytes_u8(&msgheader, msg_type)
+        || !WPACKET_put_bytes_u24(&msgheader, msg_len)
+        || !WPACKET_put_bytes_u16(&msgheader, msg_seq)
+        || !WPACKET_put_bytes_u24(&msgheader, fragoff)
+        || !WPACKET_put_bytes_u24(&msgheader, fraglen)
+        || !WPACKET_get_total_written(&msgheader, &msgheaderlen)
+        || msgheaderlen != DTLS1_HM_HEADER_LENGTH
+        || !WPACKET_finish(&msgheader))
+        return 0;
+
+    return 1;
+}
+
 /*
  * send s->init_buf in records of type 'type' (SSL3_RT_HANDSHAKE or
  * SSL3_RT_CHANGE_CIPHER_SPEC)
@@ -117,11 +140,11 @@ int dtls1_do_write(SSL_CONNECTION *s, uint8_t type)
     size_t written;
     size_t curr_mtu;
     int retry = 1;
-    size_t len, overhead, used_len, msg_len;
+    size_t len, overhead, used_len, msg_len = 0;
     SSL *ssl = SSL_CONNECTION_GET_SSL(s);
     unsigned char *data = (unsigned char *)s->init_buf->data;
     unsigned short msg_seq = s->d1->w_msg_hdr.seq;
-    unsigned char msg_type;
+    unsigned char msg_type = 0;
 
     if (type == SSL3_RT_HANDSHAKE) {
         msg_type = *data++;
@@ -152,6 +175,8 @@ int dtls1_do_write(SSL_CONNECTION *s, uint8_t type)
 
     /* s->init_num shouldn't ever be < 0...but just in case */
     while (s->init_num > 0) {
+        unsigned char *msgstart;
+
         if (type == SSL3_RT_HANDSHAKE && s->init_off > 0) {
             /*
              * We must be writing a fragment other than the first one
@@ -207,29 +232,25 @@ int dtls1_do_write(SSL_CONNECTION *s, uint8_t type)
         if (len > ssl_get_max_send_fragment(s))
             len = ssl_get_max_send_fragment(s);
 
-        /*
-         * XDTLS: this function is too long.  split out the CCS part
-         */
+        msgstart = (unsigned char *)&s->init_buf->data[s->init_off];
+
         if (type == SSL3_RT_HANDSHAKE) {
-            unsigned char *p = (unsigned char *)&s->init_buf->data[s->init_off];
+            const size_t fragoff = s->init_off;
+            const size_t fraglen = len - DTLS1_HM_HEADER_LENGTH;
 
-            if (len < DTLS1_HM_HEADER_LENGTH) {
+            if (len < DTLS1_HM_HEADER_LENGTH
+                    || !dtls1_write_hm_header(msgstart, msg_type, msg_len,
+                                              msg_seq, fragoff, fraglen))
                 /*
                  * len is so small that we really can't do anything sensible
                  * so fail
                  */
                 return -1;
-            }
-
-            *p++ = msg_type;
-            l2n3(msg_len, p);
-            s2n(msg_seq, p);
-            l2n3(s->init_off, p);
-            l2n3(len - DTLS1_HM_HEADER_LENGTH, p);
         }
-        unsigned char *msgstart = (unsigned char *)&s->init_buf->data[s->init_off];
 
-        if (dtls1_write_bytes(s, type, msgstart, len, &written) <= 0) {
+        ret = dtls1_write_bytes(s, type, msgstart, len, &written);
+
+        if (ret <= 0) {
             /*
              * might need to update MTU here, but we don't know which
              * previous packet caused the failure -- so can't really
@@ -275,12 +296,10 @@ int dtls1_do_write(SSL_CONNECTION *s, uint8_t type)
                      * reconstruct message header is if it is being sent in
                      * single fragment
                      */
-                    *msgstart++ = msg_type;
-                    l2n3(msg_len, msgstart);
-                    s2n(msg_seq, msgstart);
-                    l2n3(0, msgstart);
-                    l2n3(msg_len, msgstart);
-                    msgstart -= DTLS1_HM_HEADER_LENGTH;
+                    if (!dtls1_write_hm_header(msgstart, msg_type, msg_len,
+                                               msg_seq, s->init_off, msg_len))
+                        return -1;
+
                     xlen = written;
                 } else {
                     msgstart += DTLS1_HM_HEADER_LENGTH;