Refactor channel binding code to fetch cbind_data only when necessary

As things stand now, channel binding data is fetched from OpenSSL and
saved into the SCRAM exchange context for any SSL connection attempted
for a SCRAM authentication, resulting in data fetched but not used if no
channel binding is used or if a different channel binding type is used
than what the data is here for.

Refactor the code in such a way that binding data is fetched from the
SSL stack only when a specific channel binding is used for both the
frontend and the backend.  In order to achieve that, save the libpq
connection context directly in the SCRAM exchange state, and add a
dependency to SSL in the low-level SCRAM routines.

This makes the interface in charge of initializing the SCRAM context
cleaner as all its data comes from either PGconn* (for frontend) or
Port* (for the backend).

Author: Michael Paquier <michael.paquier@gmail.com>

src/backend/libpq/auth-scram.c

@@ -110,10 +110,8 @@ typedef struct
 
 	const char *username;		/* username from startup packet */
 
+	Port	   *port;
 	char		cbind_flag;
-	bool		ssl_in_use;
-	const char *tls_finished_message;
-	size_t		tls_finished_len;
 	char	   *channel_binding_type;
 
 	int			iterations;
@@ -172,21 +170,15 @@ static char *scram_mock_salt(const char *username);
  * it will fail, as if an incorrect password was given.
  */
 void *
-pg_be_scram_init(const char *username,
-				 const char *shadow_pass,
-				 bool ssl_in_use,
-				 const char *tls_finished_message,
-				 size_t tls_finished_len)
+pg_be_scram_init(Port *port,
+				 const char *shadow_pass)
 {
 	scram_state *state;
 	bool		got_verifier;
 
 	state = (scram_state *) palloc0(sizeof(scram_state));
+	state->port = port;
 	state->state = SCRAM_AUTH_INIT;
-	state->username = username;
-	state->ssl_in_use = ssl_in_use;
-	state->tls_finished_message = tls_finished_message;
-	state->tls_finished_len = tls_finished_len;
 	state->channel_binding_type = NULL;
 
 	/*
@@ -209,7 +201,7 @@ pg_be_scram_init(const char *username,
 				 */
 				ereport(LOG,
 						(errmsg("invalid SCRAM verifier for user \"%s\"",
-								username)));
+								state->port->user_name)));
 				got_verifier = false;
 			}
 		}
@@ -220,7 +212,7 @@ pg_be_scram_init(const char *username,
 			 * authentication with an MD5 hash.)
 			 */
 			state->logdetail = psprintf(_("User \"%s\" does not have a valid SCRAM verifier."),
-										state->username);
+										state->port->user_name);
 			got_verifier = false;
 		}
 	}
@@ -242,8 +234,8 @@ pg_be_scram_init(const char *username,
 	 */
 	if (!got_verifier)
 	{
-		mock_scram_verifier(username, &state->iterations, &state->salt,
-							state->StoredKey, state->ServerKey);
+		mock_scram_verifier(state->port->user_name, &state->iterations,
+							&state->salt, state->StoredKey, state->ServerKey);
 		state->doomed = true;
 	}
 
@@ -815,7 +807,7 @@ read_client_first_message(scram_state *state, char *input)
 			 * it supports channel binding, which in this implementation is
 			 * the case if a connection is using SSL.
 			 */
-			if (state->ssl_in_use)
+			if (state->port->ssl_in_use)
 				ereport(ERROR,
 						(errcode(ERRCODE_INVALID_AUTHORIZATION_SPECIFICATION),
 						 errmsg("SCRAM channel binding negotiation error"),
@@ -839,7 +831,7 @@ read_client_first_message(scram_state *state, char *input)
 			{
 				char	   *channel_binding_type;
 
-				if (!state->ssl_in_use)
+				if (!state->port->ssl_in_use)
 				{
 					/*
 					 * Without SSL, we don't support channel binding.
@@ -1120,8 +1112,9 @@ read_client_final_message(scram_state *state, char *input)
 		 */
 		if (strcmp(state->channel_binding_type, SCRAM_CHANNEL_BINDING_TLS_UNIQUE) == 0)
 		{
-			cbind_data = state->tls_finished_message;
-			cbind_data_len = state->tls_finished_len;
+#ifdef USE_SSL
+			cbind_data = be_tls_get_peer_finished(state->port, &cbind_data_len);
+#endif
 		}
 		else
 		{

src/backend/libpq/auth.c

@@ -873,8 +873,6 @@ CheckSCRAMAuth(Port *port, char *shadow_pass, char **logdetail)
 	int			inputlen;
 	int			result;
 	bool		initial;
-	char	   *tls_finished = NULL;
-	size_t		tls_finished_len = 0;
 
 	/*
 	 * SASL auth is not supported for protocol versions before 3, because it
@@ -915,17 +913,6 @@ CheckSCRAMAuth(Port *port, char *shadow_pass, char **logdetail)
 	sendAuthRequest(port, AUTH_REQ_SASL, sasl_mechs, p - sasl_mechs + 1);
 	pfree(sasl_mechs);
 
-#ifdef USE_SSL
-
-	/*
-	 * Get data for channel binding.
-	 */
-	if (port->ssl_in_use)
-	{
-		tls_finished = be_tls_get_peer_finished(port, &tls_finished_len);
-	}
-#endif
-
 	/*
 	 * Initialize the status tracker for message exchanges.
 	 *
@@ -937,11 +924,7 @@ CheckSCRAMAuth(Port *port, char *shadow_pass, char **logdetail)
 	 * This is because we don't want to reveal to an attacker what usernames
 	 * are valid, nor which users have a valid password.
 	 */
-	scram_opaq = pg_be_scram_init(port->user_name,
-								  shadow_pass,
-								  port->ssl_in_use,
-								  tls_finished,
-								  tls_finished_len);
+	scram_opaq = pg_be_scram_init(port, shadow_pass);
 
 	/*
 	 * Loop through SASL message exchange.  This exchange can consist of

src/include/libpq/scram.h

@@ -13,15 +13,15 @@
 #ifndef PG_SCRAM_H
 #define PG_SCRAM_H
 
+#include "libpq/libpq-be.h"
+
 /* Status codes for message exchange */
 #define SASL_EXCHANGE_CONTINUE		0
 #define SASL_EXCHANGE_SUCCESS		1
 #define SASL_EXCHANGE_FAILURE		2
 
 /* Routines dedicated to authentication */
-extern void *pg_be_scram_init(const char *username, const char *shadow_pass,
-				 bool ssl_in_use, const char *tls_finished_message,
-				 size_t tls_finished_len);
+extern void *pg_be_scram_init(Port *port, const char *shadow_pass);
 extern int pg_be_scram_exchange(void *opaq, char *input, int inputlen,
 					 char **output, int *outputlen, char **logdetail);
 

src/interfaces/libpq/fe-auth.c

@@ -491,8 +491,6 @@ pg_SASL_init(PGconn *conn, int payloadlen)
 	bool		success;
 	const char *selected_mechanism;
 	PQExpBufferData mechanism_buf;
-	char	   *tls_finished = NULL;
-	size_t		tls_finished_len = 0;
 	char	   *password;
 
 	initPQExpBuffer(&mechanism_buf);
@@ -570,32 +568,15 @@ pg_SASL_init(PGconn *conn, int payloadlen)
 		goto error;
 	}
 
-#ifdef USE_SSL
-
-	/*
-	 * Get data for channel binding.
-	 */
-	if (strcmp(selected_mechanism, SCRAM_SHA256_PLUS_NAME) == 0)
-	{
-		tls_finished = pgtls_get_finished(conn, &tls_finished_len);
-		if (tls_finished == NULL)
-			goto oom_error;
-	}
-#endif
-
 	/*
 	 * Initialize the SASL state information with all the information gathered
 	 * during the initial exchange.
 	 *
 	 * Note: Only tls-unique is supported for the moment.
 	 */
-	conn->sasl_state = pg_fe_scram_init(conn->pguser,
+	conn->sasl_state = pg_fe_scram_init(conn,
 										password,
-										conn->ssl_in_use,
-										selected_mechanism,
-										conn->scram_channel_binding,
-										tls_finished,
-										tls_finished_len);
+										selected_mechanism);
 	if (!conn->sasl_state)
 		goto oom_error;
 
@@ -603,7 +584,7 @@ pg_SASL_init(PGconn *conn, int payloadlen)
 	pg_fe_scram_exchange(conn->sasl_state,
 						 NULL, -1,
 						 &initialresponse, &initialresponselen,
-						 &done, &success, &conn->errorMessage);
+						 &done, &success);
 
 	if (done && !success)
 		goto error;
@@ -684,7 +665,7 @@ pg_SASL_continue(PGconn *conn, int payloadlen, bool final)
 	pg_fe_scram_exchange(conn->sasl_state,
 						 challenge, payloadlen,
 						 &output, &outputlen,
-						 &done, &success, &conn->errorMessage);
+						 &done, &success);
 	free(challenge);			/* don't need the input anymore */
 
 	if (final && !done)

src/interfaces/libpq/fe-auth.h

@@ -23,17 +23,13 @@ extern int	pg_fe_sendauth(AuthRequest areq, int payloadlen, PGconn *conn);
 extern char *pg_fe_getauthname(PQExpBuffer errorMessage);
 
 /* Prototypes for functions in fe-auth-scram.c */
-extern void *pg_fe_scram_init(const char *username,
+extern void *pg_fe_scram_init(PGconn *conn,
 				 const char *password,
-				 bool ssl_in_use,
-				 const char *sasl_mechanism,
-				 const char *channel_binding_type,
-				 char *tls_finished_message,
-				 size_t tls_finished_len);
+				 const char *sasl_mechanism);
 extern void pg_fe_scram_free(void *opaq);
 extern void pg_fe_scram_exchange(void *opaq, char *input, int inputlen,
 					 char **output, int *outputlen,
-					 bool *done, bool *success, PQExpBuffer errorMessage);
+					 bool *done, bool *success);
 extern char *pg_fe_scram_build_verifier(const char *password);
 
 #endif							/* FE_AUTH_H */