Refactor permissions-checking for role grants.

Instead of having checks in AddRoleMems() and DelRoleMems(), have
the callers perform checks where it's required. In some cases it
isn't, either because the caller has already performed a check for
the same condition, or because the check couldn't possibly fail.

The "Skip permission check if nothing to do" check in each of
AddRoleMems() and DelRoleMems() is pointless. Some call sites
can't pass an empty list. Others can, but in those cases, the role
being modified is one that the current user has just created.
Therefore, they must have permission to modify it, and so no
permission check is required at all.

This patch is intended to have no user-visible consequences. It is
intended to simplify future work in this area.

Patch by me, reviewed by Mark Dilger.

Discussion: http://postgr.es/m/CA+TgmobFzTLkLwOquFrAcdsWBsOWDr-_H-jw+qBvfx-wSzMwDA@mail.gmail.com

src/backend/commands/user.c

@@ -94,6 +94,8 @@ static void DelRoleMems(const char *rolename, Oid roleid,
 						List *memberSpecs, List *memberIds,
 						Oid grantorId, GrantRoleOptions *popt,
 						DropBehavior behavior);
+static void check_role_membership_authorization(Oid currentUserId, Oid roleid,
+												bool is_grant);
 static Oid	check_role_grantor(Oid currentUserId, Oid roleid, Oid grantorId,
 							   bool is_grant);
 static RevokeRoleGrantAction *initialize_revoke_actions(CatCList *memlist);
@@ -505,6 +507,8 @@ CreateRole(ParseState *pstate, CreateRoleStmt *stmt)
 			Oid			oldroleid = oldroleform->oid;
 			char	   *oldrolename = NameStr(oldroleform->rolname);
 
+			/* can only add this role to roles for which you have rights */
+			check_role_membership_authorization(GetUserId(), oldroleid, true);
 			AddRoleMems(oldrolename, oldroleid,
 						thisrole_list,
 						thisrole_oidlist,
@@ -517,6 +521,9 @@ CreateRole(ParseState *pstate, CreateRoleStmt *stmt)
 	/*
 	 * Add the specified members to this new role. adminmembers get the admin
 	 * option, rolemembers don't.
+	 *
+	 * NB: No permissions check is required here. If you have enough rights
+	 * to create a role, you can add any members you like.
 	 */
 	AddRoleMems(stmt->role, roleid,
 				rolemembers, roleSpecsToIds(rolemembers),
@@ -1442,6 +1449,8 @@ GrantRole(ParseState *pstate, GrantRoleStmt *stmt)
 					 errmsg("column names cannot be included in GRANT/REVOKE ROLE")));
 
 		roleid = get_role_oid(rolename, false);
+		check_role_membership_authorization(GetUserId(), roleid,
+											stmt->is_grant);
 		if (stmt->is_grant)
 			AddRoleMems(rolename, roleid,
 						stmt->grantee_roles, grantee_ids,
@@ -1566,43 +1575,6 @@ AddRoleMems(const char *rolename, Oid roleid,
 
 	Assert(list_length(memberSpecs) == list_length(memberIds));
 
-	/* Skip permission check if nothing to do */
-	if (!memberIds)
-		return;
-
-	/*
-	 * Check permissions: must have createrole or admin option on the role to
-	 * be changed.  To mess with a superuser role, you gotta be superuser.
-	 */
-	if (superuser_arg(roleid))
-	{
-		if (!superuser())
-			ereport(ERROR,
-					(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
-					 errmsg("must be superuser to alter superusers")));
-	}
-	else
-	{
-		if (!have_createrole_privilege() &&
-			!is_admin_of_role(currentUserId, roleid))
-			ereport(ERROR,
-					(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
-					 errmsg("must have admin option on role \"%s\"",
-							rolename)));
-	}
-
-	/*
-	 * The charter of pg_database_owner is to have exactly one, implicit,
-	 * situation-dependent member.  There's no technical need for this
-	 * restriction.  (One could lift it and take the further step of making
-	 * object_ownercheck(DatabaseRelationId, ...) equivalent to has_privs_of_role(roleid,
-	 * ROLE_PG_DATABASE_OWNER), in which case explicit, situation-independent
-	 * members could act as the owner of any database.)
-	 */
-	if (roleid == ROLE_PG_DATABASE_OWNER)
-		ereport(ERROR,
-				errmsg("role \"%s\" cannot have explicit members", rolename));
-
 	/* Validate grantor (and resolve implicit grantor if not specified). */
 	grantorId = check_role_grantor(currentUserId, roleid, grantorId, true);
 
@@ -1902,31 +1874,6 @@ DelRoleMems(const char *rolename, Oid roleid,
 
 	Assert(list_length(memberSpecs) == list_length(memberIds));
 
-	/* Skip permission check if nothing to do */
-	if (!memberIds)
-		return;
-
-	/*
-	 * Check permissions: must have createrole or admin option on the role to
-	 * be changed.  To mess with a superuser role, you gotta be superuser.
-	 */
-	if (superuser_arg(roleid))
-	{
-		if (!superuser())
-			ereport(ERROR,
-					(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
-					 errmsg("must be superuser to alter superusers")));
-	}
-	else
-	{
-		if (!have_createrole_privilege() &&
-			!is_admin_of_role(currentUserId, roleid))
-			ereport(ERROR,
-					(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
-					 errmsg("must have admin option on role \"%s\"",
-							rolename)));
-	}
-
 	/* Validate grantor (and resolve implicit grantor if not specified). */
 	grantorId = check_role_grantor(currentUserId, roleid, grantorId, false);
 
@@ -2040,6 +1987,51 @@ DelRoleMems(const char *rolename, Oid roleid,
 	table_close(pg_authmem_rel, NoLock);
 }
 
+/*
+ * Check that currentUserId has permission to modify the membership list for
+ * roleid. Throw an error if not.
+ */
+static void
+check_role_membership_authorization(Oid currentUserId, Oid roleid,
+									bool is_grant)
+{
+	/*
+	 * The charter of pg_database_owner is to have exactly one, implicit,
+	 * situation-dependent member.  There's no technical need for this
+	 * restriction.  (One could lift it and take the further step of making
+	 * object_ownercheck(DatabaseRelationId, ...) equivalent to
+	 * has_privs_of_role(roleid, ROLE_PG_DATABASE_OWNER), in which case
+	 * explicit, situation-independent members could act as the owner of any
+	 * database.)
+	 */
+	if (is_grant && roleid == ROLE_PG_DATABASE_OWNER)
+		ereport(ERROR,
+				errmsg("role \"%s\" cannot have explicit members",
+					   GetUserNameFromId(roleid, false)));
+
+	/* To mess with a superuser role, you gotta be superuser. */
+	if (superuser_arg(roleid))
+	{
+		if (!superuser_arg(currentUserId))
+			ereport(ERROR,
+					(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
+					 errmsg("must be superuser to alter superusers")));
+	}
+	else
+	{
+		/*
+		 * Otherwise, must have createrole or admin option on the role to be
+		 * changed.
+		 */
+		if (!has_createrole_privilege(currentUserId) &&
+			!is_admin_of_role(currentUserId, roleid))
+			ereport(ERROR,
+					(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
+					 errmsg("must have admin option on role \"%s\"",
+							GetUserNameFromId(roleid, false))));
+	}
+}
+
 /*
  * Sanity-check, or infer, the grantor for a GRANT or REVOKE statement
  * targeting a role.