Implement the Opaque PRF Input TLS extension
(draft-rescorla-tls-opaque-prf-input-00.txt), and do some cleanups and
bugfixes on the way. In particular, this fixes the buffer bounds
checks in ssl_add_clienthello_tlsext() and in ssl_add_serverhello_tlsext().
Note that the opaque PRF Input TLS extension is not compiled by default;
see CHANGES.
diff --git a/ssl/t1_lib.c b/ssl/t1_lib.c
index b5eab2c..0c78414 100644
--- a/ssl/t1_lib.c
+++ b/ssl/t1_lib.c
@@ -284,8 +284,8 @@
+ hostname length
*/
- if ((lenmax = limit - p - 9) < 0
- || (size_str = strlen(s->tlsext_hostname)) > (unsigned long)lenmax)
+ if ((lenmax = limit - ret - 9) < 0
+ || (size_str = strlen(s->tlsext_hostname)) > (unsigned long)lenmax)
return NULL;
/* extension type and length */
@@ -300,15 +300,15 @@
s2n(size_str,ret);
memcpy(ret, s->tlsext_hostname, size_str);
ret+=size_str;
-
}
+
#ifndef OPENSSL_NO_EC
if (s->tlsext_ecpointformatlist != NULL)
{
/* Add TLS extension ECPointFormats to the ClientHello message */
long lenmax;
- if ((lenmax = limit - p - 5) < 0) return NULL;
+ if ((lenmax = limit - ret - 5) < 0) return NULL;
if (s->tlsext_ecpointformatlist_length > (unsigned long)lenmax) return NULL;
if (s->tlsext_ecpointformatlist_length > 255)
{
@@ -327,7 +327,7 @@
/* Add TLS extension EllipticCurves to the ClientHello message */
long lenmax;
- if ((lenmax = limit - p - 6) < 0) return NULL;
+ if ((lenmax = limit - ret - 6) < 0) return NULL;
if (s->tlsext_ellipticcurvelist_length > (unsigned long)lenmax) return NULL;
if (s->tlsext_ellipticcurvelist_length > 65532)
{
@@ -359,8 +359,7 @@
/* Check for enough room 2 for extension type, 2 for len
* rest for ticket
*/
- if (limit - p - 4 - ticklen < 0)
- return NULL;
+ if ((long)(limit - ret - 4 - ticklen) < 0) return NULL;
s2n(TLSEXT_TYPE_session_ticket,ret);
s2n(ticklen,ret);
if (ticklen)
@@ -370,6 +369,24 @@
}
}
+#ifdef TLSEXT_TYPE_opaque_prf_input
+ if (s->s3->client_opaque_prf_input != NULL)
+ {
+ size_t col = s->s3->client_opaque_prf_input_len;
+
+ if ((long)(limit - ret - 6 - col < 0))
+ return NULL;
+ if (col > 0xFFFD) /* can't happen */
+ return NULL;
+
+ s2n(TLSEXT_TYPE_opaque_prf_input, ret);
+ s2n(col + 2, ret);
+ s2n(col, ret);
+ memcpy(ret, s->s3->client_opaque_prf_input, col);
+ ret += col;
+ }
+#endif
+
if ((extdatalen = ret-p-2)== 0)
return p;
@@ -387,7 +404,7 @@
if (!s->hit && s->servername_done == 1 && s->session->tlsext_hostname != NULL)
{
- if (limit - p - 4 < 0) return NULL;
+ if ((long)(limit - ret - 4) < 0) return NULL;
s2n(TLSEXT_TYPE_server_name,ret);
s2n(0,ret);
@@ -398,7 +415,7 @@
/* Add TLS extension ECPointFormats to the ServerHello message */
long lenmax;
- if ((lenmax = limit - p - 5) < 0) return NULL;
+ if ((lenmax = limit - ret - 5) < 0) return NULL;
if (s->tlsext_ecpointformatlist_length > (unsigned long)lenmax) return NULL;
if (s->tlsext_ecpointformatlist_length > 255)
{
@@ -419,11 +436,29 @@
if (s->tlsext_ticket_expected
&& !(SSL_get_options(s) & SSL_OP_NO_TICKET))
{
- if (limit - p - 4 < 0) return NULL;
+ if ((long)(limit - ret - 4) < 0) return NULL;
s2n(TLSEXT_TYPE_session_ticket,ret);
s2n(0,ret);
}
+
+#ifdef TLSEXT_TYPE_opaque_prf_input
+ if (s->s3->server_opaque_prf_input != NULL)
+ {
+ size_t sol = s->s3->server_opaque_prf_input_len;
+ if ((long)(limit - ret - 6 - sol) < 0)
+ return NULL;
+ if (sol > 0xFFFD) /* can't happen */
+ return NULL;
+
+ s2n(TLSEXT_TYPE_opaque_prf_input, ret);
+ s2n(sol + 2, ret);
+ s2n(sol, ret);
+ memcpy(ret, s->s3->server_opaque_prf_input, sol);
+ ret += sol;
+ }
+#endif
+
if ((extdatalen = ret-p-2)== 0)
return p;
@@ -610,6 +645,35 @@
#endif
}
#endif /* OPENSSL_NO_EC */
+#ifdef TLSEXT_TYPE_opaque_prf_input
+ else if (type == TLSEXT_TYPE_opaque_prf_input)
+ {
+ unsigned char *sdata = data;
+
+ if (size < 2)
+ {
+ *al = SSL_AD_DECODE_ERROR;
+ return 0;
+ }
+ n2s(sdata, s->s3->client_opaque_prf_input_len);
+ if (s->s3->client_opaque_prf_input_len != size - 2)
+ {
+ *al = SSL_AD_DECODE_ERROR;
+ return 0;
+ }
+
+ if (s->s3->client_opaque_prf_input != NULL) /* shouldn't really happen */
+ OPENSSL_free(s->s3->client_opaque_prf_input);
+
+ s->s3->client_opaque_prf_input = BUF_memdup(sdata, s->s3->client_opaque_prf_input_len);
+ if (s->s3->client_opaque_prf_input == NULL)
+ {
+ *al = TLS1_AD_INTERNAL_ERROR;
+ return 0;
+ }
+ }
+#endif
+
/* session ticket processed earlier */
data+=size;
}
@@ -694,6 +758,35 @@
}
s->tlsext_ticket_expected = 1;
}
+#ifdef TLSEXT_TYPE_opaque_prf_input
+ else if (type == TLSEXT_TYPE_opaque_prf_input)
+ {
+ unsigned char *sdata = data;
+
+ if (size < 2)
+ {
+ *al = SSL_AD_DECODE_ERROR;
+ return 0;
+ }
+ n2s(sdata, s->s3->server_opaque_prf_input_len);
+ if (s->s3->server_opaque_prf_input_len != size - 2)
+ {
+ *al = SSL_AD_DECODE_ERROR;
+ return 0;
+ }
+
+ if (s->s3->server_opaque_prf_input != NULL) /* shouldn't really happen */
+ OPENSSL_free(s->s3->server_opaque_prf_input);
+ s->s3->server_opaque_prf_input = BUF_memdup(sdata, s->s3->server_opaque_prf_input_len);
+
+ if (s->s3->server_opaque_prf_input == NULL)
+ {
+ *al = TLS1_AD_INTERNAL_ERROR;
+ return 0;
+ }
+ }
+#endif
+
data+=size;
}
@@ -780,6 +873,38 @@
s2n(i,j);
}
#endif /* OPENSSL_NO_EC */
+
+#ifdef TLSEXT_TYPE_opaque_prf_input
+ {
+ int r = 1;
+
+ if (s->ctx->tlsext_opaque_prf_input_callback != 0)
+ {
+ r = s->ctx->tlsext_opaque_prf_input_callback(s, NULL, 0, s->ctx->tlsext_opaque_prf_input_callback_arg);
+ if (!r)
+ return -1;
+ }
+
+ if (s->tlsext_opaque_prf_input != NULL)
+ {
+ if (s->s3->client_opaque_prf_input != NULL) /* shouldn't really happen */
+ OPENSSL_free(s->s3->client_opaque_prf_input);
+
+ s->s3->client_opaque_prf_input = BUF_memdup(s->tlsext_opaque_prf_input, s->tlsext_opaque_prf_input_len);
+ if (s->s3->client_opaque_prf_input == NULL)
+ {
+ SSLerr(SSL_F_SSL_PREPARE_CLIENTHELLO_TLSEXT,ERR_R_MALLOC_FAILURE);
+ return -1;
+ }
+ s->s3->client_opaque_prf_input_len = s->tlsext_opaque_prf_input_len;
+ }
+
+ if (r == 2)
+ /* at callback's request, insist on receiving an appropriate server opaque PRF input */
+ s->s3->server_opaque_prf_input_len = s->tlsext_opaque_prf_input_len;
+ }
+#endif
+
return 1;
}
@@ -810,6 +935,7 @@
s->tlsext_ecpointformatlist[2] = TLSEXT_ECPOINTFORMAT_ansiX962_compressed_char2;
}
#endif /* OPENSSL_NO_EC */
+
return 1;
}
@@ -832,6 +958,62 @@
else if (s->initial_ctx != NULL && s->initial_ctx->tlsext_servername_callback != 0)
ret = s->initial_ctx->tlsext_servername_callback(s, &al, s->initial_ctx->tlsext_servername_arg);
+
+#ifdef TLSEXT_TYPE_opaque_prf_input
+ {
+ /* This sort of belongs into ssl_prepare_serverhello_tlsext(),
+ * but we might be sending an alert in response to the client hello,
+ * so this has to happen here in ssl_check_clienthello_tlsext(). */
+
+ int r = 1;
+
+ if (s->ctx->tlsext_opaque_prf_input_callback != 0)
+ {
+ r = s->ctx->tlsext_opaque_prf_input_callback(s, NULL, 0, s->ctx->tlsext_opaque_prf_input_callback_arg);
+ if (!r)
+ {
+ ret = SSL_TLSEXT_ERR_ALERT_FATAL;
+ al = SSL_AD_INTERNAL_ERROR;
+ goto err;
+ }
+ }
+
+ if (s->s3->server_opaque_prf_input != NULL) /* shouldn't really happen */
+ OPENSSL_free(s->s3->server_opaque_prf_input);
+ s->s3->server_opaque_prf_input = NULL;
+
+ if (s->tlsext_opaque_prf_input != NULL)
+ {
+ if (s->s3->client_opaque_prf_input != NULL &&
+ s->s3->client_opaque_prf_input_len == s->tlsext_opaque_prf_input_len)
+ {
+ /* can only use this extension if we have a server opaque PRF input
+ * of the same length as the client opaque PRF input! */
+
+ s->s3->server_opaque_prf_input = BUF_memdup(s->tlsext_opaque_prf_input, s->tlsext_opaque_prf_input_len);
+ if (s->s3->server_opaque_prf_input == NULL)
+ {
+ ret = SSL_TLSEXT_ERR_ALERT_FATAL;
+ al = SSL_AD_INTERNAL_ERROR;
+ goto err;
+ }
+ s->s3->server_opaque_prf_input_len = s->tlsext_opaque_prf_input_len;
+ }
+ }
+
+ if (r == 2 && s->s3->server_opaque_prf_input == NULL)
+ {
+ /* The callback wants to enforce use of the extension,
+ * but we can't do that with the client opaque PRF input;
+ * abort the handshake.
+ */
+ ret = SSL_TLSEXT_ERR_ALERT_FATAL;
+ al = SSL_AD_HANDSHAKE_FAILURE;
+ }
+ }
+#endif
+
+ err:
switch (ret)
{
case SSL_TLSEXT_ERR_ALERT_FATAL:
@@ -895,6 +1077,29 @@
else if (s->initial_ctx != NULL && s->initial_ctx->tlsext_servername_callback != 0)
ret = s->initial_ctx->tlsext_servername_callback(s, &al, s->initial_ctx->tlsext_servername_arg);
+#ifdef TLSEXT_TYPE_opaque_prf_input
+ if (s->s3->server_opaque_prf_input_len > 0)
+ {
+ /* This case may indicate that we, as a client, want to insist on using opaque PRF inputs.
+ * So first verify that we really have a value from the server too. */
+
+ if (s->s3->server_opaque_prf_input == NULL)
+ {
+ ret = SSL_TLSEXT_ERR_ALERT_FATAL;
+ al = SSL_AD_HANDSHAKE_FAILURE;
+ }
+
+ /* Anytime the server *has* sent an opaque PRF input, we need to check
+ * that we have a client opaque PRF input of the same size. */
+ if (s->s3->client_opaque_prf_input == NULL ||
+ s->s3->client_opaque_prf_input_len != s->s3->server_opaque_prf_input_len)
+ {
+ ret = SSL_TLSEXT_ERR_ALERT_FATAL;
+ al = SSL_AD_ILLEGAL_PARAMETER;
+ }
+ }
+#endif
+
switch (ret)
{
case SSL_TLSEXT_ERR_ALERT_FATAL:
