GSSAPI encryption support

On both the frontend and backend, prepare for GSSAPI encryption
support by moving common code for error handling into a separate file.
Fix a TODO for handling multiple status messages in the process.
Eliminate the OIDs, which have not been needed for some time.

Add frontend and backend encryption support functions.  Keep the
context initiation for authentication-only separate on both the
frontend and backend in order to avoid concerns about changing the
requested flags to include encryption support.

In postmaster, pull GSSAPI authorization checking into a shared
function.  Also share the initiator name between the encryption and
non-encryption codepaths.

For HBA, add "hostgssenc" and "hostnogssenc" entries that behave
similarly to their SSL counterparts.  "hostgssenc" requires either
"gss", "trust", or "reject" for its authentication.

Similarly, add a "gssencmode" parameter to libpq.  Supported values are
"disable", "require", and "prefer".  Notably, negotiation will only be
attempted if credentials can be acquired.  Move credential acquisition
into its own function to support this behavior.

Add a simple pg_stat_gssapi view similar to pg_stat_ssl, for monitoring
if GSSAPI authentication was used, what principal was used, and if
encryption is being used on the connection.

Finally, add documentation for everything new, and update existing
documentation on connection security.

Thanks to Michael Paquier for the Windows fixes.

Author: Robbie Harwood, with changes to the read/write functions by me.
Reviewed in various forms and at different times by: Michael Paquier,
   Andres Freund, David Steele.
Discussion: https://www.postgresql.org/message-id/flat/jlg1tgq1ktm.fsf@thriss.redhat.com

1 files changed, 43 insertions, 72 deletions

diff --git a/src/backend/libpq/auth.c b/src/backend/libpq/auth.c
index 6f03c7c2a5e..62466be7023 100644
--- a/src/backend/libpq/auth.c
+++ b/src/backend/libpq/auth.c
@@ -36,6 +36,7 @@
 #include "port/pg_bswap.h"
 #include "replication/walsender.h"
 #include "storage/ipc.h"
+#include "utils/memutils.h"
 #include "utils/timestamp.h"
 
 
@@ -172,12 +173,9 @@ bool		pg_krb_caseins_users;
  *----------------------------------------------------------------
  */
 #ifdef ENABLE_GSS
-#if defined(HAVE_GSSAPI_H)
-#include <gssapi.h>
-#else
-#include <gssapi/gssapi.h>
-#endif
+#include "be-gssapi-common.h"
 
+static int	pg_GSS_checkauth(Port *port);
 static int	pg_GSS_recvauth(Port *port);
 #endif							/* ENABLE_GSS */
 
@@ -383,6 +381,17 @@ ClientAuthentication(Port *port)
 					 errmsg("connection requires a valid client certificate")));
 	}
 
+#ifdef ENABLE_GSS
+	if (port->gss->enc && port->hba->auth_method != uaReject &&
+		port->hba->auth_method != uaImplicitReject &&
+		port->hba->auth_method != uaTrust &&
+		port->hba->auth_method != uaGSS)
+	{
+		ereport(FATAL, (errcode(ERRCODE_INVALID_AUTHORIZATION_SPECIFICATION),
+						errmsg("GSSAPI encryption can only be used with gss, trust, or reject authentication methods")));
+	}
+#endif
+
 	/*
 	 * Now proceed to do the actual authentication check
 	 */
@@ -523,8 +532,14 @@ ClientAuthentication(Port *port)
 
 		case uaGSS:
 #ifdef ENABLE_GSS
-			sendAuthRequest(port, AUTH_REQ_GSS, NULL, 0);
-			status = pg_GSS_recvauth(port);
+			port->gss->auth = true;
+			if (port->gss->enc)
+				status = pg_GSS_checkauth(port);
+			else
+			{
+				sendAuthRequest(port, AUTH_REQ_GSS, NULL, 0);
+				status = pg_GSS_recvauth(port);
+			}
 #else
 			Assert(false);
 #endif
@@ -1031,68 +1046,6 @@ CheckSCRAMAuth(Port *port, char *shadow_pass, char **logdetail)
  *----------------------------------------------------------------
  */
 #ifdef ENABLE_GSS
-
-#if defined(WIN32) && !defined(_MSC_VER)
-/*
- * MIT Kerberos GSSAPI DLL doesn't properly export the symbols for MingW
- * that contain the OIDs required. Redefine here, values copied
- * from src/athena/auth/krb5/src/lib/gssapi/generic/gssapi_generic.c
- */
-static const gss_OID_desc GSS_C_NT_USER_NAME_desc =
-{10, (void *) "\x2a\x86\x48\x86\xf7\x12\x01\x02\x01\x02"};
-static GSS_DLLIMP gss_OID GSS_C_NT_USER_NAME = &GSS_C_NT_USER_NAME_desc;
-#endif
-
-
-/*
- * Generate an error for GSSAPI authentication.  The caller should apply
- * _() to errmsg to make it translatable.
- */
-static void
-pg_GSS_error(int severity, const char *errmsg, OM_uint32 maj_stat, OM_uint32 min_stat)
-{
-	gss_buffer_desc gmsg;
-	OM_uint32	lmin_s,
-				msg_ctx;
-	char		msg_major[128],
-				msg_minor[128];
-
-	/* Fetch major status message */
-	msg_ctx = 0;
-	gss_display_status(&lmin_s, maj_stat, GSS_C_GSS_CODE,
-					   GSS_C_NO_OID, &msg_ctx, &gmsg);
-	strlcpy(msg_major, gmsg.value, sizeof(msg_major));
-	gss_release_buffer(&lmin_s, &gmsg);
-
-	if (msg_ctx)
-
-		/*
-		 * More than one message available. XXX: Should we loop and read all
-		 * messages? (same below)
-		 */
-		ereport(WARNING,
-				(errmsg_internal("incomplete GSS error report")));
-
-	/* Fetch mechanism minor status message */
-	msg_ctx = 0;
-	gss_display_status(&lmin_s, min_stat, GSS_C_MECH_CODE,
-					   GSS_C_NO_OID, &msg_ctx, &gmsg);
-	strlcpy(msg_minor, gmsg.value, sizeof(msg_minor));
-	gss_release_buffer(&lmin_s, &gmsg);
-
-	if (msg_ctx)
-		ereport(WARNING,
-				(errmsg_internal("incomplete GSS minor error report")));
-
-	/*
-	 * errmsg_internal, since translation of the first part must be done
-	 * before calling this function anyway.
-	 */
-	ereport(severity,
-			(errmsg_internal("%s", errmsg),
-			 errdetail_internal("%s: %s", msg_major, msg_minor)));
-}
-
 static int
 pg_GSS_recvauth(Port *port)
 {
@@ -1101,7 +1054,6 @@ pg_GSS_recvauth(Port *port)
 				lmin_s,
 				gflags;
 	int			mtype;
-	int			ret;
 	StringInfoData buf;
 	gss_buffer_desc gbuf;
 
@@ -1254,10 +1206,23 @@ pg_GSS_recvauth(Port *port)
 		 */
 		gss_release_cred(&min_stat, &port->gss->cred);
 	}
+	return pg_GSS_checkauth(port);
+}
+
+/*
+ * Check whether the GSSAPI-authenticated user is allowed to connect as the
+ * claimed username.
+ */
+static int
+pg_GSS_checkauth(Port *port)
+{
+	int			ret;
+	OM_uint32	maj_stat,
+				min_stat,
+				lmin_s;
+	gss_buffer_desc gbuf;
 
 	/*
-	 * GSS_S_COMPLETE indicates that authentication is now complete.
-	 *
 	 * Get the name of the user that authenticated, and compare it to the pg
 	 * username that was specified for the connection.
 	 */
@@ -1268,6 +1233,12 @@ pg_GSS_recvauth(Port *port)
 					 maj_stat, min_stat);
 
 	/*
+	 * Copy the original name of the authenticated principal into our backend
+	 * memory for display later.
+	 */
+	port->gss->princ = MemoryContextStrdup(TopMemoryContext, gbuf.value);
+
+	/*
 	 * Split the username at the realm separator
 	 */
 	if (strchr(gbuf.value, '@'))