Support SCRAM-SHA-256 authentication (RFC 5802 and 7677).

This introduces a new generic SASL authentication method, similar to the
GSS and SSPI methods. The server first tells the client which SASL
authentication mechanism to use, and then the mechanism-specific SASL
messages are exchanged in AuthenticationSASLcontinue and PasswordMessage
messages. Only SCRAM-SHA-256 is supported at the moment, but this allows
adding more SASL mechanisms in the future, without changing the overall
protocol.

Support for channel binding, aka SCRAM-SHA-256-PLUS is left for later.

The SASLPrep algorithm, for pre-processing the password, is not yet
implemented. That could cause trouble, if you use a password with
non-ASCII characters, and a client library that does implement SASLprep.
That will hopefully be added later.

Authorization identities, as specified in the SCRAM-SHA-256 specification,
are ignored. SET SESSION AUTHORIZATION provides more or less the same
functionality, anyway.

If a user doesn't exist, perform a "mock" authentication, by constructing
an authentic-looking challenge on the fly. The challenge is derived from
a new system-wide random value, "mock authentication nonce", which is
created at initdb, and stored in the control file. We go through these
motions, in order to not give away the information on whether the user
exists, to unauthenticated users.

Bumps PG_CONTROL_VERSION, because of the new field in control file.

Patch by Michael Paquier and Heikki Linnakangas, reviewed at different
stages by Robert Haas, Stephen Frost, David Steele, Aleksander Alekseev,
and many others.

Discussion: https://www.postgresql.org/message-id/CAB7nPqRbR3GmFYdedCAhzukfKrgBLTLtMvENOmPrVWREsZkF8g%40mail.gmail.com
Discussion: https://www.postgresql.org/message-id/CAB7nPqSMXU35g%3DW9X74HVeQp0uvgJxvYOuA4A-A3M%2B0wfEBv-w%40mail.gmail.com
Discussion: https://www.postgresql.org/message-id/55192AFE.6080106@iki.fi

1 files changed, 24 insertions, 0 deletions

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 897358342db..744360c7696 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -65,6 +65,7 @@
 #include "storage/reinit.h"
 #include "storage/smgr.h"
 #include "storage/spin.h"
+#include "utils/backend_random.h"
 #include "utils/builtins.h"
 #include "utils/guc.h"
 #include "utils/memutils.h"
@@ -4665,6 +4666,16 @@ GetSystemIdentifier(void)
 }
 
 /*
+ * Returns the random nonce from control file.
+ */
+char *
+GetMockAuthenticationNonce(void)
+{
+	Assert(ControlFile != NULL);
+	return ControlFile->mock_authentication_nonce;
+}
+
+/*
  * Are checksums enabled for data pages?
  */
 bool
@@ -4914,6 +4925,7 @@ BootStrapXLOG(void)
 	char	   *recptr;
 	bool		use_existent;
 	uint64		sysidentifier;
+	char		mock_auth_nonce[MOCK_AUTH_NONCE_LEN];
 	struct timeval tv;
 	pg_crc32c	crc;
 
@@ -4934,6 +4946,17 @@ BootStrapXLOG(void)
 	sysidentifier |= ((uint64) tv.tv_usec) << 12;
 	sysidentifier |= getpid() & 0xFFF;
 
+	/*
+	 * Generate a random nonce. This is used for authentication requests
+	 * that will fail because the user does not exist. The nonce is used to
+	 * create a genuine-looking password challenge for the non-existent user,
+	 * in lieu of an actual stored password.
+	 */
+	if (!pg_backend_random(mock_auth_nonce, MOCK_AUTH_NONCE_LEN))
+		ereport(PANIC,
+			(errcode(ERRCODE_INTERNAL_ERROR),
+			 errmsg("could not generation secret authorization token")));
+
 	/* First timeline ID is always 1 */
 	ThisTimeLineID = 1;
 
@@ -5040,6 +5063,7 @@ BootStrapXLOG(void)
 	memset(ControlFile, 0, sizeof(ControlFileData));
 	/* Initialize pg_control status fields */
 	ControlFile->system_identifier = sysidentifier;
+	memcpy(ControlFile->mock_authentication_nonce, mock_auth_nonce, MOCK_AUTH_NONCE_LEN);
 	ControlFile->state = DB_SHUTDOWNED;
 	ControlFile->time = checkPoint.time;
 	ControlFile->checkPoint = checkPoint.redo;