Revert commit 4a56d9a2

We have been unable to trace the contributor of that code to gain their
agreement for the licence change so the code has to be removed.

This commit reverts that contribution. The contribution had no functional
impact so the original way of doing things is still valid. However the
surrounding code has changed significantly so that the exact code as it
was orignally cannot be used. This commit uses the original code as a basis,
but rewrites it to use the PACKET API.
Reviewed-by: NRichard Levitte <levitte@openssl.org>
Reviewed-by: NRich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5808)

ssl/statem/statem_srvr.c

@@ -3233,11 +3233,9 @@ static int tls_process_cke_gost(SSL *s, PACKET *pkt)
     const unsigned char *start;
     size_t outlen = 32, inlen;
     unsigned long alg_a;
-    int Ttag, Tclass;
-    long Tlen;
-    size_t sess_key_len;
-    const unsigned char *data;
+    unsigned int asn1id, asn1len;
     int ret = 0;
+    PACKET encdata;
 
     /* Get our certificate private key */
     alg_a = s->s3->tmp.new_cipher->algorithm_auth;
@@ -3279,22 +3277,42 @@ static int tls_process_cke_gost(SSL *s, PACKET *pkt)
             ERR_clear_error();
     }
     /* Decrypt session key */
-    sess_key_len = PACKET_remaining(pkt);
-    if (!PACKET_get_bytes(pkt, &data, sess_key_len)) {
-        SSLfatal(s, SSL_AD_INTERNAL_ERROR, SSL_F_TLS_PROCESS_CKE_GOST,
-                 ERR_R_INTERNAL_ERROR);
+    if (!PACKET_get_1(pkt, &asn1id)
+            || asn1id != (V_ASN1_SEQUENCE | V_ASN1_CONSTRUCTED)
+            || !PACKET_peek_1(pkt, &asn1len)) {
+        SSLfatal(s, SSL_AD_DECODE_ERROR, SSL_F_TLS_PROCESS_CKE_GOST,
+                 SSL_R_DECRYPTION_FAILED);
         goto err;
     }
-    /* TODO(size_t): Convert this function */
-    if (ASN1_get_object((const unsigned char **)&data, &Tlen, &Ttag,
-                        &Tclass, (long)sess_key_len) != V_ASN1_CONSTRUCTED
-        || Ttag != V_ASN1_SEQUENCE || Tclass != V_ASN1_UNIVERSAL) {
+    if (asn1len == 0x81) {
+        /*
+         * Long form length. Should only be one byte of length. Anything else
+         * isn't supported.
+         * We did a successful peek before so this shouldn't fail
+         */
+        if (!PACKET_forward(pkt, 1)) {
+            SSLfatal(s, SSL_AD_INTERNAL_ERROR, SSL_F_TLS_PROCESS_CKE_GOST,
+                     SSL_R_DECRYPTION_FAILED);
+            goto err;
+        }
+    } else  if (asn1len >= 0x80) {
+        /*
+         * Indefinite length, or more than one long form length bytes. We don't
+         * support it
+         */
+        SSLfatal(s, SSL_AD_DECODE_ERROR, SSL_F_TLS_PROCESS_CKE_GOST,
+                 SSL_R_DECRYPTION_FAILED);
+        goto err;
+    } /* else short form length */
+
+    if (!PACKET_as_length_prefixed_1(pkt, &encdata)) {
         SSLfatal(s, SSL_AD_DECODE_ERROR, SSL_F_TLS_PROCESS_CKE_GOST,
                  SSL_R_DECRYPTION_FAILED);
         goto err;
     }
-    start = data;
-    inlen = Tlen;
+    inlen = PACKET_remaining(&encdata);
+    start = PACKET_data(&encdata);
+
     if (EVP_PKEY_decrypt(pkey_ctx, premaster_secret, &outlen, start,
                          inlen) <= 0) {
         SSLfatal(s, SSL_AD_DECODE_ERROR, SSL_F_TLS_PROCESS_CKE_GOST,