Fix bugs in manipulation of large objects.

tglsfdc · tglsfdc · commit 152bfc0af89d · 2023-12-15T13:55:05.000-05:00
In v16 and up (since commit afbfc02), large object ownership checking has been broken because object_ownercheck() didn't take care of the discrepancy between our object-address representation of large objects (classId == LargeObjectRelationId) and the catalog where their ownership info is actually stored (LargeObjectMetadataRelationId). This resulted in failures such as "unrecognized class ID: 2613" when trying to update blob properties as a non-superuser. Poking around for related bugs, I found that AlterObjectOwner_internal would pass the wrong classId to the PostAlterHook in the no-op code path where the large object already has the desired owner. Also, recordExtObjInitPriv checked for the wrong classId; that bug is only latent because the stanza is dead code anyway, but as long as we're carrying it around it should be less wrong. These bugs are quite old. In HEAD, we can reduce the scope for future bugs of this ilk by changing AlterObjectOwner_internal's API to let the translation happen inside that function, rather than requiring callers to know about it. A more bulletproof fix, perhaps, would be to start using LargeObjectMetadataRelationId as the dependency and object-address classId for blobs. However that has substantial risk of breaking third-party code; even within our own code, it'd create hassles for pg_dump which would have to cope with a version-dependent representation. For now, keep the status quo. Discussion: https://postgr.es/m/2650449.1702497209@sss.pgh.pa.us
diff --git a/src/backend/catalog/aclchk.c b/src/backend/catalog/aclchk.c
@@ -3967,9 +3967,14 @@ object_ownercheck(Oid classid, Oid objectid, Oid roleid)
 	if (superuser_arg(roleid))
 		return true;
 
+	/* For large objects, the catalog to consult is pg_largeobject_metadata */
+	if (classid == LargeObjectRelationId)
+		classid = LargeObjectMetadataRelationId;
+
 	cacheid = get_object_catcache_oid(classid);
 	if (cacheid != -1)
 	{
+		/* we can get the object's tuple from the syscache */
 		HeapTuple	tuple;
 
 		tuple = SearchSysCache1(cacheid, ObjectIdGetDatum(objectid));
@@ -3986,7 +3991,6 @@ object_ownercheck(Oid classid, Oid objectid, Oid roleid)
 	else
 	{
 		/* for catalogs without an appropriate syscache */
-
 		Relation	rel;
 		ScanKeyData entry[1];
 		SysScanDesc scan;
@@ -4306,9 +4310,9 @@ recordExtObjInitPriv(Oid objoid, Oid classoid)
 
 		ReleaseSysCache(tuple);
 	}
-	/* pg_largeobject_metadata */
-	else if (classoid == LargeObjectMetadataRelationId)
+	else if (classoid == LargeObjectRelationId)
 	{
+		/* For large objects, we must consult pg_largeobject_metadata */
 		Datum		aclDatum;
 		bool		isNull;
 		HeapTuple	tuple;
diff --git a/src/backend/catalog/pg_shdepend.c b/src/backend/catalog/pg_shdepend.c
@@ -1618,6 +1618,10 @@ shdepReassignOwned(List *roleids, Oid newrole)
 						Oid			classId = sdepForm->classid;
 						Relation	catalog;
 
+						/*
+						 * For large objects, the catalog to modify is
+						 * pg_largeobject_metadata
+						 */
 						if (classId == LargeObjectRelationId)
 							classId = LargeObjectMetadataRelationId;
 
diff --git a/src/backend/commands/alter.c b/src/backend/commands/alter.c
@@ -929,9 +929,8 @@ ExecAlterOwnerStmt(AlterOwnerStmt *stmt)
 				classId = address.classId;
 
 				/*
-				 * XXX - get_object_address returns Oid of pg_largeobject
-				 * catalog for OBJECT_LARGEOBJECT because of historical
-				 * reasons.  Fix up it here.
+				 * For large objects, the catalog to modify is
+				 * pg_largeobject_metadata
 				 */
 				if (classId == LargeObjectRelationId)
 					classId = LargeObjectMetadataRelationId;
@@ -1075,16 +1074,31 @@ AlterObjectOwner_internal(Relation rel, Oid objectId, Oid new_ownerId)
 		/* Perform actual update */
 		CatalogTupleUpdate(rel, &newtup->t_self, newtup);
 
-		/* Update owner dependency reference */
+		/*
+		 * Update owner dependency reference.  When working on a large object,
+		 * we have to translate back to the OID conventionally used for LOs'
+		 * classId.
+		 */
 		if (classId == LargeObjectMetadataRelationId)
 			classId = LargeObjectRelationId;
+
 		changeDependencyOnOwner(classId, objectId, new_ownerId);
 
 		/* Release memory */
 		pfree(values);
 		pfree(nulls);
 		pfree(replaces);
 	}
+	else
+	{
+		/*
+		 * No need to change anything.  But when working on a large object, we
+		 * have to translate back to the OID conventionally used for LOs'
+		 * classId, or the post-alter hook (if any) will get confused.
+		 */
+		if (classId == LargeObjectMetadataRelationId)
+			classId = LargeObjectRelationId;
+	}
 
 	InvokeObjectPostAlterHook(classId, objectId, 0);
 }
diff --git a/src/backend/libpq/be-fsstubs.c b/src/backend/libpq/be-fsstubs.c
@@ -43,7 +43,7 @@
 #include <unistd.h>
 
 #include "access/xact.h"
-#include "catalog/pg_largeobject_metadata.h"
+#include "catalog/pg_largeobject.h"
 #include "libpq/be-fsstubs.h"
 #include "libpq/libpq-fs.h"
 #include "miscadmin.h"
@@ -323,7 +323,7 @@ be_lo_unlink(PG_FUNCTION_ARGS)
 	 * relevant FDs.
 	 */
 	if (!lo_compat_privileges &&
-		!object_ownercheck(LargeObjectMetadataRelationId, lobjId, GetUserId()))
+		!object_ownercheck(LargeObjectRelationId, lobjId, GetUserId()))
 		ereport(ERROR,
 				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
 				 errmsg("must be owner of large object %u", lobjId)));
diff --git a/src/backend/storage/large_object/inv_api.c b/src/backend/storage/large_object/inv_api.c
@@ -221,11 +221,10 @@ inv_create(Oid lobjId)
 	/*
 	 * dependency on the owner of largeobject
 	 *
-	 * The reason why we use LargeObjectRelationId instead of
-	 * LargeObjectMetadataRelationId here is to provide backward compatibility
-	 * to the applications which utilize a knowledge about internal layout of
-	 * system catalogs. OID of pg_largeobject_metadata and loid of
-	 * pg_largeobject are same value, so there are no actual differences here.
+	 * Note that LO dependencies are recorded using classId
+	 * LargeObjectRelationId for backwards-compatibility reasons.  Using
+	 * LargeObjectMetadataRelationId instead would simplify matters for the
+	 * backend, but it'd complicate pg_dump and possibly break other clients.
 	 */
 	recordDependencyOnOwner(LargeObjectRelationId,
 							lobjId_new, GetUserId());
diff --git a/src/test/regress/expected/largeobject.out b/src/test/regress/expected/largeobject.out
@@ -6,7 +6,7 @@
 \getenv abs_builddir PG_ABS_BUILDDIR
 -- ensure consistent test output regardless of the default bytea format
 SET bytea_output TO escape;
--- Test ALTER LARGE OBJECT OWNER, GRANT, COMMENT
+-- Test ALTER LARGE OBJECT OWNER
 CREATE ROLE regress_lo_user;
 SELECT lo_create(42);
  lo_create 
@@ -15,8 +15,11 @@ SELECT lo_create(42);
 (1 row)
 
 ALTER LARGE OBJECT 42 OWNER TO regress_lo_user;
+-- Test GRANT, COMMENT as non-superuser
+SET SESSION AUTHORIZATION regress_lo_user;
 GRANT SELECT ON LARGE OBJECT 42 TO public;
 COMMENT ON LARGE OBJECT 42 IS 'the ultimate answer';
+RESET SESSION AUTHORIZATION;
 -- Test psql's \lo_list et al (we assume no other LOs exist yet)
 \lo_list
                Large objects
diff --git a/src/test/regress/expected/largeobject_1.out b/src/test/regress/expected/largeobject_1.out
@@ -6,7 +6,7 @@
 \getenv abs_builddir PG_ABS_BUILDDIR
 -- ensure consistent test output regardless of the default bytea format
 SET bytea_output TO escape;
--- Test ALTER LARGE OBJECT OWNER, GRANT, COMMENT
+-- Test ALTER LARGE OBJECT OWNER
 CREATE ROLE regress_lo_user;
 SELECT lo_create(42);
  lo_create 
@@ -15,8 +15,11 @@ SELECT lo_create(42);
 (1 row)
 
 ALTER LARGE OBJECT 42 OWNER TO regress_lo_user;
+-- Test GRANT, COMMENT as non-superuser
+SET SESSION AUTHORIZATION regress_lo_user;
 GRANT SELECT ON LARGE OBJECT 42 TO public;
 COMMENT ON LARGE OBJECT 42 IS 'the ultimate answer';
+RESET SESSION AUTHORIZATION;
 -- Test psql's \lo_list et al (we assume no other LOs exist yet)
 \lo_list
                Large objects
diff --git a/src/test/regress/sql/largeobject.sql b/src/test/regress/sql/largeobject.sql
@@ -9,13 +9,19 @@
 -- ensure consistent test output regardless of the default bytea format
 SET bytea_output TO escape;
 
--- Test ALTER LARGE OBJECT OWNER, GRANT, COMMENT
+-- Test ALTER LARGE OBJECT OWNER
 CREATE ROLE regress_lo_user;
 SELECT lo_create(42);
 ALTER LARGE OBJECT 42 OWNER TO regress_lo_user;
+
+-- Test GRANT, COMMENT as non-superuser
+SET SESSION AUTHORIZATION regress_lo_user;
+
 GRANT SELECT ON LARGE OBJECT 42 TO public;
 COMMENT ON LARGE OBJECT 42 IS 'the ultimate answer';
 
+RESET SESSION AUTHORIZATION;
+
 -- Test psql's \lo_list et al (we assume no other LOs exist yet)
 \lo_list
 \lo_list+
