Subject: [PATCH] CREATE INDEX: use the original userid for more ACL checks.

From: Noah Misch <[email-masked]>
Date: Sat, 25 Jun 2022 09:07:41 -0700

Commit a117cebd638dd02e5c2e791c25e43745f233111b used the original userid
for ACL checks located directly in DefineIndex(), but it still adopted
the table owner userid for more ACL checks than intended.  That broke
dump/reload of indexes that refer to an operator class, collation, or
exclusion operator in a schema other than "public" or "pg_catalog".
Back-patch to v10 (all supported versions), like the earlier commit.

Nathan Bossart and Noah Misch

Discussion: https://postgr.es/m/[email-masked]
---
 contrib/citext/Makefile                      |    2 
 contrib/citext/expected/create_index_acl.out |   81 +++++++++++++++++++++++
 contrib/citext/sql/create_index_acl.sql      |   82 ++++++++++++++++++++++++
 src/backend/commands/indexcmds.c             |   92 +++++++++++++++++++++++----
 4 files changed, 244 insertions(+), 13 deletions(-)
 create mode 100644 contrib/citext/expected/create_index_acl.out
 create mode 100644 contrib/citext/sql/create_index_acl.sql

--- a/contrib/citext/Makefile
+++ b/contrib/citext/Makefile
@@ -7,7 +7,7 @@
        citext--1.1--1.0.sql citext--unpackaged--1.0.sql
 PGFILEDESC = "citext - case-insensitive character string data type"
 
-REGRESS = citext
+REGRESS = create_index_acl citext
 
 ifdef USE_PGXS
 PG_CONFIG = pg_config
--- /dev/null
+++ b/contrib/citext/expected/create_index_acl.out
@@ -0,0 +1,81 @@
+-- Each DefineIndex() ACL check uses either the original userid or the table
+-- owner userid; see its header comment.  Here, confirm that DefineIndex()
+-- uses its original userid where necessary.  The test works by creating
+-- indexes that refer to as many sorts of objects as possible, with the table
+-- owner having as few applicable privileges as possible.  (The privileges.sql
+-- regress_sro_user tests look for the opposite defect; they confirm that
+-- DefineIndex() uses the table owner userid where necessary.)
+-- Don't override tablespaces; this version lacks allow_in_place_tablespaces.
+BEGIN;
+CREATE ROLE regress_minimal;
+CREATE SCHEMA s;
+CREATE EXTENSION citext SCHEMA s;
+-- Revoke all conceivably-relevant ACLs within the extension.  The system
+-- doesn't check all these ACLs, but this will provide some coverage if that
+-- ever changes.
+REVOKE ALL ON TYPE s.citext FROM PUBLIC;
+REVOKE ALL ON FUNCTION s.citext_lt(s.citext, s.citext) FROM PUBLIC;
+REVOKE ALL ON FUNCTION s.citext_le(s.citext, s.citext) FROM PUBLIC;
+REVOKE ALL ON FUNCTION s.citext_eq(s.citext, s.citext) FROM PUBLIC;
+REVOKE ALL ON FUNCTION s.citext_ge(s.citext, s.citext) FROM PUBLIC;
+REVOKE ALL ON FUNCTION s.citext_gt(s.citext, s.citext) FROM PUBLIC;
+REVOKE ALL ON FUNCTION s.citext_cmp(s.citext, s.citext) FROM PUBLIC;
+-- Functions sufficient for making an index column that has the side effect of
+-- changing search_path at expression planning time.
+CREATE FUNCTION public.setter() RETURNS bool VOLATILE
+  LANGUAGE SQL AS $$SET search_path = s; SELECT true$$;
+CREATE FUNCTION s.const() RETURNS bool IMMUTABLE
+  LANGUAGE SQL AS $$SELECT public.setter()$$;
+CREATE FUNCTION s.index_this_expr(s.citext, bool) RETURNS s.citext IMMUTABLE
+  LANGUAGE SQL AS $$SELECT $1$$;
+REVOKE ALL ON FUNCTION public.setter() FROM PUBLIC;
+REVOKE ALL ON FUNCTION s.const() FROM PUBLIC;
+REVOKE ALL ON FUNCTION s.index_this_expr(s.citext, bool) FROM PUBLIC;
+-- Even for an empty table, expression planning calls s.const & public.setter.
+GRANT EXECUTE ON FUNCTION public.setter() TO regress_minimal;
+GRANT EXECUTE ON FUNCTION s.const() TO regress_minimal;
+-- Function for index predicate.
+CREATE FUNCTION s.index_row_if(s.citext) RETURNS bool IMMUTABLE
+  LANGUAGE SQL AS $$SELECT $1 IS NOT NULL$$;
+REVOKE ALL ON FUNCTION s.index_row_if(s.citext) FROM PUBLIC;
+-- Even for an empty table, CREATE INDEX checks ii_Predicate permissions.
+GRANT EXECUTE ON FUNCTION s.index_row_if(s.citext) TO regress_minimal;
+-- Non-extension, non-function objects.
+CREATE COLLATION s.coll (LOCALE="C");
+CREATE TABLE s.x (y s.citext);
+ALTER TABLE s.x OWNER TO regress_minimal;
+-- Empty-table DefineIndex()
+CREATE UNIQUE INDEX u0rows ON s.x USING btree
+  ((s.index_this_expr(y, s.const())) COLLATE s.coll s.citext_ops)
+  WHERE s.index_row_if(y);
+ALTER TABLE s.x ADD CONSTRAINT e0rows EXCLUDE USING btree
+  ((s.index_this_expr(y, s.const())) COLLATE s.coll WITH s.=)
+  WHERE (s.index_row_if(y));
+-- Make the table nonempty.
+INSERT INTO s.x VALUES ('foo'), ('bar');
+-- If the INSERT runs the planner on index expressions, a search_path change
+-- survives.  As of 2022-06, the INSERT reuses a cached plan.  It does so even
+-- under debug_discard_caches, since each index is new-in-transaction.  If
+-- future work changes a cache lifecycle, this RESET may become necessary.
+RESET search_path;
+-- For a nonempty table, owner needs permissions throughout ii_Expressions.
+GRANT EXECUTE ON FUNCTION s.index_this_expr(s.citext, bool) TO regress_minimal;
+CREATE UNIQUE INDEX u2rows ON s.x USING btree
+  ((s.index_this_expr(y, s.const())) COLLATE s.coll s.citext_ops)
+  WHERE s.index_row_if(y);
+ALTER TABLE s.x ADD CONSTRAINT e2rows EXCLUDE USING btree
+  ((s.index_this_expr(y, s.const())) COLLATE s.coll WITH s.=)
+  WHERE (s.index_row_if(y));
+-- Shall not find s.coll via search_path, despite the s.const->public.setter
+-- call having set search_path=s during expression planning.  Suppress the
+-- message itself, which depends on the database encoding.
+\set VERBOSITY terse
+DO $$
+BEGIN
+ALTER TABLE s.x ADD CONSTRAINT underqualified EXCLUDE USING btree
+  ((s.index_this_expr(y, s.const())) COLLATE coll WITH s.=)
+  WHERE (s.index_row_if(y));
+EXCEPTION WHEN OTHERS THEN RAISE EXCEPTION '%', sqlstate; END$$;
+ERROR:  42704
+\set VERBOSITY default
+ROLLBACK;
--- /dev/null
+++ b/contrib/citext/sql/create_index_acl.sql
@@ -0,0 +1,82 @@
+-- Each DefineIndex() ACL check uses either the original userid or the table
+-- owner userid; see its header comment.  Here, confirm that DefineIndex()
+-- uses its original userid where necessary.  The test works by creating
+-- indexes that refer to as many sorts of objects as possible, with the table
+-- owner having as few applicable privileges as possible.  (The privileges.sql
+-- regress_sro_user tests look for the opposite defect; they confirm that
+-- DefineIndex() uses the table owner userid where necessary.)
+
+-- Don't override tablespaces; this version lacks allow_in_place_tablespaces.
+
+BEGIN;
+CREATE ROLE regress_minimal;
+CREATE SCHEMA s;
+CREATE EXTENSION citext SCHEMA s;
+-- Revoke all conceivably-relevant ACLs within the extension.  The system
+-- doesn't check all these ACLs, but this will provide some coverage if that
+-- ever changes.
+REVOKE ALL ON TYPE s.citext FROM PUBLIC;
+REVOKE ALL ON FUNCTION s.citext_lt(s.citext, s.citext) FROM PUBLIC;
+REVOKE ALL ON FUNCTION s.citext_le(s.citext, s.citext) FROM PUBLIC;
+REVOKE ALL ON FUNCTION s.citext_eq(s.citext, s.citext) FROM PUBLIC;
+REVOKE ALL ON FUNCTION s.citext_ge(s.citext, s.citext) FROM PUBLIC;
+REVOKE ALL ON FUNCTION s.citext_gt(s.citext, s.citext) FROM PUBLIC;
+REVOKE ALL ON FUNCTION s.citext_cmp(s.citext, s.citext) FROM PUBLIC;
+-- Functions sufficient for making an index column that has the side effect of
+-- changing search_path at expression planning time.
+CREATE FUNCTION public.setter() RETURNS bool VOLATILE
+  LANGUAGE SQL AS $$SET search_path = s; SELECT true$$;
+CREATE FUNCTION s.const() RETURNS bool IMMUTABLE
+  LANGUAGE SQL AS $$SELECT public.setter()$$;
+CREATE FUNCTION s.index_this_expr(s.citext, bool) RETURNS s.citext IMMUTABLE
+  LANGUAGE SQL AS $$SELECT $1$$;
+REVOKE ALL ON FUNCTION public.setter() FROM PUBLIC;
+REVOKE ALL ON FUNCTION s.const() FROM PUBLIC;
+REVOKE ALL ON FUNCTION s.index_this_expr(s.citext, bool) FROM PUBLIC;
+-- Even for an empty table, expression planning calls s.const & public.setter.
+GRANT EXECUTE ON FUNCTION public.setter() TO regress_minimal;
+GRANT EXECUTE ON FUNCTION s.const() TO regress_minimal;
+-- Function for index predicate.
+CREATE FUNCTION s.index_row_if(s.citext) RETURNS bool IMMUTABLE
+  LANGUAGE SQL AS $$SELECT $1 IS NOT NULL$$;
+REVOKE ALL ON FUNCTION s.index_row_if(s.citext) FROM PUBLIC;
+-- Even for an empty table, CREATE INDEX checks ii_Predicate permissions.
+GRANT EXECUTE ON FUNCTION s.index_row_if(s.citext) TO regress_minimal;
+-- Non-extension, non-function objects.
+CREATE COLLATION s.coll (LOCALE="C");
+CREATE TABLE s.x (y s.citext);
+ALTER TABLE s.x OWNER TO regress_minimal;
+-- Empty-table DefineIndex()
+CREATE UNIQUE INDEX u0rows ON s.x USING btree
+  ((s.index_this_expr(y, s.const())) COLLATE s.coll s.citext_ops)
+  WHERE s.index_row_if(y);
+ALTER TABLE s.x ADD CONSTRAINT e0rows EXCLUDE USING btree
+  ((s.index_this_expr(y, s.const())) COLLATE s.coll WITH s.=)
+  WHERE (s.index_row_if(y));
+-- Make the table nonempty.
+INSERT INTO s.x VALUES ('foo'), ('bar');
+-- If the INSERT runs the planner on index expressions, a search_path change
+-- survives.  As of 2022-06, the INSERT reuses a cached plan.  It does so even
+-- under debug_discard_caches, since each index is new-in-transaction.  If
+-- future work changes a cache lifecycle, this RESET may become necessary.
+RESET search_path;
+-- For a nonempty table, owner needs permissions throughout ii_Expressions.
+GRANT EXECUTE ON FUNCTION s.index_this_expr(s.citext, bool) TO regress_minimal;
+CREATE UNIQUE INDEX u2rows ON s.x USING btree
+  ((s.index_this_expr(y, s.const())) COLLATE s.coll s.citext_ops)
+  WHERE s.index_row_if(y);
+ALTER TABLE s.x ADD CONSTRAINT e2rows EXCLUDE USING btree
+  ((s.index_this_expr(y, s.const())) COLLATE s.coll WITH s.=)
+  WHERE (s.index_row_if(y));
+-- Shall not find s.coll via search_path, despite the s.const->public.setter
+-- call having set search_path=s during expression planning.  Suppress the
+-- message itself, which depends on the database encoding.
+\set VERBOSITY terse
+DO $$
+BEGIN
+ALTER TABLE s.x ADD CONSTRAINT underqualified EXCLUDE USING btree
+  ((s.index_this_expr(y, s.const())) COLLATE coll WITH s.=)
+  WHERE (s.index_row_if(y));
+EXCEPTION WHEN OTHERS THEN RAISE EXCEPTION '%', sqlstate; END$$;
+\set VERBOSITY default
+ROLLBACK;
--- a/src/backend/commands/indexcmds.c
+++ b/src/backend/commands/indexcmds.c
@@ -65,7 +65,10 @@
 				  Oid relId,
 				  char *accessMethodName, Oid accessMethodId,
 				  bool amcanorder,
-				  bool isconstraint);
+				  bool isconstraint,
+				  Oid ddl_userid,
+				  int ddl_sec_context,
+				  int *ddl_save_nestlevel);
 static Oid GetIndexOpClass(List *opclass, Oid attrType,
 				char *accessMethodName, Oid accessMethodId);
 static char *ChooseIndexName(const char *tabname, Oid namespaceId,
@@ -168,8 +171,7 @@
 	 * Compute the operator classes, collations, and exclusion operators for
 	 * the new index, so we can test whether it's compatible with the existing
 	 * one.  Note that ComputeIndexAttrs might fail here, but that's OK:
-	 * DefineIndex would have called this function with the same arguments
-	 * later on, and it would have failed then anyway.
+	 * DefineIndex would have failed later.
 	 */
 	indexInfo = makeNode(IndexInfo);
 	indexInfo->ii_Expressions = NIL;
@@ -187,7 +189,7 @@
 					  coloptions, attributeList,
 					  exclusionOpNames, relationId,
 					  accessMethodName, accessMethodId,
-					  amcanorder, isconstraint);
+					  amcanorder, isconstraint, InvalidOid, 0, NULL);

 	/* Get the soon-obsolete pg_index tuple. */
@@ -280,6 +282,19 @@
  * DefineIndex
  *		Creates a new index.
  *
+ * This function manages the current userid according to the needs of pg_dump.
+ * Recreating old-database catalog entries in new-database is fine, regardless
+ * of which users would have permission to recreate those entries now.  That's
+ * just preservation of state.  Running opaque expressions, like calling a
+ * function named in a catalog entry or evaluating a pg_node_tree in a catalog
+ * entry, as anyone other than the object owner, is not fine.  To adhere to
+ * those principles and to remain fail-safe, use the table owner userid for
+ * most ACL checks.  Use the original userid for ACL checks reached without
+ * traversing opaque expressions.  (pg_dump can predict such ACL checks from
+ * catalogs.)  Overall, this is a mess.  Future DDL development should
+ * consider offering one DDL command for catalog setup and a separate DDL
+ * command for steps that run opaque expressions.
+ *
  * 'relationId': the OID of the heap relation on which the index is to be
  *		created
  * 'stmt': IndexStmt describing the properties of the new index.
@@ -581,7 +596,8 @@
 					  coloptions, stmt->indexParams,
 					  stmt->excludeOpNames, relationId,
 					  accessMethodName, accessMethodId,
-					  amcanorder, stmt->isconstraint);
+					  amcanorder, stmt->isconstraint, root_save_userid,
+					  root_save_sec_context, &root_save_nestlevel);
 
 	/*
 	 * Extra checks when creating a PRIMARY KEY index.
@@ -639,9 +655,8 @@
 
 	/*
 	 * Roll back any GUC changes executed by index functions, and keep
-	 * subsequent changes local to this command.  It's barely possible that
-	 * some index function changed a behavior-affecting GUC, e.g. xmloption,
-	 * that affects subsequent steps.
+	 * subsequent changes local to this command.  This is essential if some
+	 * index function changed a behavior-affecting GUC, e.g. search_path.
 	 */
 	AtEOXact_GUC(false, root_save_nestlevel);
 	root_save_nestlevel = NewGUCNestLevel();
@@ -996,6 +1011,10 @@
 /*
  * Compute per-index-column information, including indexed column numbers
  * or index expressions, opclasses, and indoptions.
+ *
+ * If the caller switched to the table owner, ddl_userid is the role for ACL
+ * checks reached without traversing opaque expressions.  Otherwise, it's
+ * InvalidOid, and other ddl_* arguments are undefined.
  */
 static void
 ComputeIndexAttrs(IndexInfo *indexInfo,
@@ -1009,11 +1028,16 @@
 				  char *accessMethodName,
 				  Oid accessMethodId,
 				  bool amcanorder,
-				  bool isconstraint)
+				  bool isconstraint,
+				  Oid ddl_userid,
+				  int ddl_sec_context,
+				  int *ddl_save_nestlevel)
 {
 	ListCell   *nextExclOp;
 	ListCell   *lc;
 	int			attn;
+	Oid			save_userid;
+	int			save_sec_context;
 
 	/* Allocate space for exclusion operator info, if needed */
 	if (exclusionOpNames)
@@ -1029,6 +1053,9 @@
 	else
 		nextExclOp = NULL;
 
+	if (OidIsValid(ddl_userid))
+		GetUserIdAndSecContext(&save_userid, &save_sec_context);
+
 	/*
 	 * process attributeList
 	 */
@@ -1123,10 +1150,24 @@
 		typeOidP[attn] = atttype;
 
 		/*
-		 * Apply collation override if any
+		 * Apply collation override if any.  Use of ddl_userid is necessary
+		 * due to ACL checks therein, and it's safe because collations don't
+		 * contain opaque expressions (or non-opaque expressions).
 		 */
 		if (attribute->collation)
+		{
+			if (OidIsValid(ddl_userid))
+			{
+				AtEOXact_GUC(false, *ddl_save_nestlevel);
+				SetUserIdAndSecContext(ddl_userid, ddl_sec_context);
+			}
 			attcollation = get_collation_oid(attribute->collation, false);
+			if (OidIsValid(ddl_userid))
+			{
+				SetUserIdAndSecContext(save_userid, save_sec_context);
+				*ddl_save_nestlevel = NewGUCNestLevel();
+			}
+		}
 
 		/*
 		 * Check we have a collation iff it's a collatable type.  The only
@@ -1154,12 +1195,25 @@
 		collationOidP[attn] = attcollation;
 
 		/*
-		 * Identify the opclass to use.
+		 * Identify the opclass to use.  Use of ddl_userid is necessary due to
+		 * ACL checks therein.  This is safe despite opclasses containing
+		 * opaque expressions (specifically, functions), because only
+		 * superusers can define opclasses.
 		 */
+		if (OidIsValid(ddl_userid))
+		{
+			AtEOXact_GUC(false, *ddl_save_nestlevel);
+			SetUserIdAndSecContext(ddl_userid, ddl_sec_context);
+		}
 		classOidP[attn] = GetIndexOpClass(attribute->opclass,
 										  atttype,
 										  accessMethodName,
 										  accessMethodId);
+		if (OidIsValid(ddl_userid))
+		{
+			SetUserIdAndSecContext(save_userid, save_sec_context);
+			*ddl_save_nestlevel = NewGUCNestLevel();
+		}
 
 		/*
 		 * Identify the exclusion operator, if any.
@@ -1173,9 +1227,23 @@
 
 			/*
 			 * Find the operator --- it must accept the column datatype
-			 * without runtime coercion (but binary compatibility is OK)
+			 * without runtime coercion (but binary compatibility is OK).
+			 * Operators contain opaque expressions (specifically, functions).
+			 * compatible_oper_opid() boils down to oper() and
+			 * IsBinaryCoercible().  PostgreSQL would have security problems
+			 * elsewhere if oper() started calling opaque expressions.
 			 */
+			if (OidIsValid(ddl_userid))
+			{
+				AtEOXact_GUC(false, *ddl_save_nestlevel);
+				SetUserIdAndSecContext(ddl_userid, ddl_sec_context);
+			}
 			opid = compatible_oper_opid(opname, atttype, atttype, false);
+			if (OidIsValid(ddl_userid))
+			{
+				SetUserIdAndSecContext(save_userid, save_sec_context);
+				*ddl_save_nestlevel = NewGUCNestLevel();
+			}
 
 			/*
 			 * Only allow commutative operators to be used in exclusion

--Gfegn71+neI+QTr7--