Restrict the privileges of CREATEROLE users.

Previously, CREATEROLE users were permitted to make nearly arbitrary
changes to roles that they didn't create, with certain exceptions,
particularly superuser roles.  Instead, allow CREATEROLE users to make such
changes to roles for which they possess ADMIN OPTION, and to
grant membership only in roles for which they possess ADMIN OPTION.

When a CREATEROLE user who is not a superuser creates a role, grant
ADMIN OPTION on the newly-created role to the creator, so that they
can administer roles they create or for which they have been given
privileges.

With these changes, CREATEROLE users still have very significant
powers that unprivileged users do not receive: they can alter, rename,
drop, comment on, change the password for, and change security labels
on roles.  However, they can now do these things only for roles for
which they possess appropriate privileges, rather than all
non-superuser roles; moreover, they cannot grant a role such as
pg_execute_server_program unless they themselves possess it.

Patch by me, reviewed by Mark Dilger.

Discussion: https://postgr.es/m/CA+TgmobN59ct+Emmz6ig1Nua2Q-_o=r6DSD98KfU53kctq_kQw@mail.gmail.com

1 files changed, 74 insertions, 26 deletions

diff --git a/src/backend/commands/user.c b/src/backend/commands/user.c
index bc2b95ac814..1ae2d0a66fb 100644
--- a/src/backend/commands/user.c
+++ b/src/backend/commands/user.c
@@ -520,6 +520,42 @@ CreateRole(ParseState *pstate, CreateRoleStmt *stmt)
 	}
 
 	/*
+	 * If the current user isn't a superuser, make them an admin of the new
+	 * role so that they can administer the new object they just created.
+	 * Superusers will be able to do that anyway.
+	 *
+	 * The grantor of record for this implicit grant is the bootstrap
+	 * superuser, which means that the CREATEROLE user cannot revoke the
+	 * grant. They can however grant the created role back to themselves
+	 * with different options, since they enjoy ADMIN OPTION on it.
+	 */
+	if (!superuser())
+	{
+		RoleSpec   *current_role = makeNode(RoleSpec);
+		GrantRoleOptions	poptself;
+
+		current_role->roletype = ROLESPEC_CURRENT_ROLE;
+		current_role->location = -1;
+
+		poptself.specified = GRANT_ROLE_SPECIFIED_ADMIN
+			| GRANT_ROLE_SPECIFIED_INHERIT
+			| GRANT_ROLE_SPECIFIED_SET;
+		poptself.admin = true;
+		poptself.inherit = false;
+		poptself.set = false;
+
+		AddRoleMems(BOOTSTRAP_SUPERUSERID, stmt->role, roleid,
+					list_make1(current_role), list_make1_oid(GetUserId()),
+					BOOTSTRAP_SUPERUSERID, &poptself);
+
+		/*
+		 * We must make the implicit grant visible to the code below, else
+		 * the additional grants will fail.
+		 */
+		CommandCounterIncrement();
+	}
+
+	/*
 	 * Add the specified members to this new role. adminmembers get the admin
 	 * option, rolemembers don't.
 	 *
@@ -694,9 +730,7 @@ AlterRole(ParseState *pstate, AlterRoleStmt *stmt)
 	/*
 	 * To mess with a superuser or replication role in any way you gotta be
 	 * superuser.  We also insist on superuser to change the BYPASSRLS
-	 * property.  Otherwise, if you don't have createrole, you're only allowed
-	 * to (1) change your own password or (2) add members to a role for which
-	 * you have ADMIN OPTION.
+	 * property.
 	 */
 	if (authform->rolsuper || dissuper)
 	{
@@ -719,29 +753,35 @@ AlterRole(ParseState *pstate, AlterRoleStmt *stmt)
 					(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
 					 errmsg("must be superuser to change bypassrls attribute")));
 	}
-	else if (!have_createrole_privilege())
+
+	/*
+	 * Most changes to a role require that you both have CREATEROLE privileges
+	 * and also ADMIN OPTION on the role.
+	 */
+	if (!have_createrole_privilege() ||
+		!is_admin_of_role(GetUserId(), roleid))
 	{
-		/* things you certainly can't do without CREATEROLE */
+		/* things an unprivileged user certainly can't do */
 		if (dinherit || dcreaterole || dcreatedb || dcanlogin || dconnlimit ||
 			dvalidUntil)
 			ereport(ERROR,
 					(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
 					 errmsg("permission denied")));
 
-		/* without CREATEROLE, can only change your own password */
+		/* an unprivileged user can change their own password */
 		if (dpassword && roleid != currentUserId)
 			ereport(ERROR,
 					(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
 					 errmsg("must have CREATEROLE privilege to change another user's password")));
-
-		/* without CREATEROLE, can only add members to roles you admin */
-		if (drolemembers && !is_admin_of_role(currentUserId, roleid))
-			ereport(ERROR,
-					(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
-					 errmsg("must have admin option on role \"%s\" to add members",
-							rolename)));
 	}
 
+	/* To add members to a role, you need ADMIN OPTION. */
+	if (drolemembers && !is_admin_of_role(currentUserId, roleid))
+		ereport(ERROR,
+				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
+				 errmsg("must have admin option on role \"%s\" to add members",
+						rolename)));
+
 	/* Convert validuntil to internal form */
 	if (dvalidUntil)
 	{
@@ -935,8 +975,9 @@ AlterRoleSet(AlterRoleSetStmt *stmt)
 		shdepLockAndCheckObject(AuthIdRelationId, roleid);
 
 		/*
-		 * To mess with a superuser you gotta be superuser; else you need
-		 * createrole, or just want to change your own settings
+		 * To mess with a superuser you gotta be superuser; otherwise you
+		 * need CREATEROLE plus admin option on the target role; unless you're
+		 * just trying to change your own settings
 		 */
 		if (roleform->rolsuper)
 		{
@@ -947,7 +988,9 @@ AlterRoleSet(AlterRoleSetStmt *stmt)
 		}
 		else
 		{
-			if (!have_createrole_privilege() && roleid != GetUserId())
+			if ((!have_createrole_privilege() ||
+				!is_admin_of_role(GetUserId(), roleid))
+				&& roleid != GetUserId())
 				ereport(ERROR,
 						(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
 						 errmsg("permission denied")));
@@ -1067,13 +1110,18 @@ DropRole(DropRoleStmt *stmt)
 
 		/*
 		 * For safety's sake, we allow createrole holders to drop ordinary
-		 * roles but not superuser roles.  This is mainly to avoid the
-		 * scenario where you accidentally drop the last superuser.
+		 * roles but not superuser roles, and only if they also have ADMIN
+		 * OPTION.
 		 */
 		if (roleform->rolsuper && !superuser())
 			ereport(ERROR,
 					(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
 					 errmsg("must be superuser to drop superusers")));
+		if (!is_admin_of_role(GetUserId(), roleid))
+			ereport(ERROR,
+					(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
+					 errmsg("must have admin option on role \"%s\"",
+							role)));
 
 		/* DROP hook for the role being removed */
 		InvokeObjectDropHook(AuthIdRelationId, roleid, 0);
@@ -1312,7 +1360,8 @@ RenameRole(const char *oldname, const char *newname)
 				 errmsg("role \"%s\" already exists", newname)));
 
 	/*
-	 * createrole is enough privilege unless you want to mess with a superuser
+	 * Only superusers can mess with superusers. Otherwise, a user with
+	 * CREATEROLE can rename a role for which they have ADMIN OPTION.
 	 */
 	if (((Form_pg_authid) GETSTRUCT(oldtuple))->rolsuper)
 	{
@@ -1323,7 +1372,8 @@ RenameRole(const char *oldname, const char *newname)
 	}
 	else
 	{
-		if (!have_createrole_privilege())
+		if (!have_createrole_privilege() ||
+			!is_admin_of_role(GetUserId(), roleid))
 			ereport(ERROR,
 					(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
 					 errmsg("permission denied to rename role")));
@@ -2023,11 +2073,9 @@ check_role_membership_authorization(Oid currentUserId, Oid roleid,
 	else
 	{
 		/*
-		 * Otherwise, must have createrole or admin option on the role to be
-		 * changed.
+		 * Otherwise, must have admin option on the role to be changed.
 		 */
-		if (!has_createrole_privilege(currentUserId) &&
-			!is_admin_of_role(currentUserId, roleid))
+		if (!is_admin_of_role(currentUserId, roleid))
 			ereport(ERROR,
 					(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
 					 errmsg("must have admin option on role \"%s\"",
@@ -2049,7 +2097,7 @@ check_role_membership_authorization(Oid currentUserId, Oid roleid,
  * be passed as InvalidOid, and this function will infer the user to be
  * recorded as the grantor. In many cases, this will be the current user, but
  * things get more complicated when the current user doesn't possess ADMIN
- * OPTION on the role but rather relies on having CREATEROLE privileges, or
+ * OPTION on the role but rather relies on having SUPERUSER privileges, or
  * on inheriting the privileges of a role which does have ADMIN OPTION. See
  * below for details.
  *
@@ -2075,7 +2123,7 @@ check_role_grantor(Oid currentUserId, Oid roleid, Oid grantorId, bool is_grant)
 		 * not depend on any other existing grants, so always default to this
 		 * interpretation when possible.
 		 */
-		if (has_createrole_privilege(currentUserId))
+		if (superuser_arg(currentUserId))
 			return BOOTSTRAP_SUPERUSERID;
 
 		/*