v9-0001-Fix-accessing-other-sessions-temp-tables.patch

From d76a774110a933ee0c9b7061391d81644bfb6371 Mon Sep 17 00:00:00 2001
From: Daniil Davidov <d.davydov@postgrespro.ru>
Date: Thu, 25 Sep 2025 20:06:40 +0700
Subject: [PATCH v9] Fix accessing other sessions temp tables

---
 src/backend/catalog/namespace.c  | 56 ++++++++++++++++++++------------
 src/backend/commands/tablecmds.c |  3 +-
 src/backend/nodes/makefuncs.c    |  6 +++-
 src/backend/parser/gram.y        | 11 ++++++-
 src/include/catalog/namespace.h  |  2 ++
 5 files changed, 55 insertions(+), 23 deletions(-)

diff --git a/src/backend/catalog/namespace.c b/src/backend/catalog/namespace.c
index ed9aeee24bc..3dee97e8ef1 100644
--- a/src/backend/catalog/namespace.c
+++ b/src/backend/catalog/namespace.c
@@ -498,28 +498,44 @@ RangeVarGetRelidExtended(const RangeVar *relation, LOCKMODE lockmode,
 		 */
 		if (relation->relpersistence == RELPERSISTENCE_TEMP)
 		{
-			if (!OidIsValid(myTempNamespace))
-				relId = InvalidOid; /* this probably can't happen? */
-			else
-			{
-				if (relation->schemaname)
-				{
-					Oid			namespaceId;
+			Oid	namespaceId;
 
-					namespaceId = LookupExplicitNamespace(relation->schemaname, missing_ok);
+			if (relation->schemaname)
+			{
+				namespaceId = LookupExplicitNamespace(relation->schemaname, missing_ok);
 
+				/*
+				 * If the user has specified an existing temporary schema
+				 * owned by another user.
+				 */
+				if (OidIsValid(namespaceId) && namespaceId != myTempNamespace)
+				{
 					/*
-					 * For missing_ok, allow a non-existent schema name to
-					 * return InvalidOid.
+					 * We don't allow users to access temp tables of other
+					 * sessions except for the case of dropping tables.
 					 */
-					if (namespaceId != myTempNamespace)
+					if (!(flags & RVR_OTHER_TEMP_OK))
 						ereport(ERROR,
-								(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
-								 errmsg("temporary tables cannot specify a schema name")));
+								(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+								 errmsg("cannot access temporary relations of other sessions")));
 				}
+			}
+			else
+			{
+				namespaceId = myTempNamespace;
 
-				relId = get_relname_relid(relation->relname, myTempNamespace);
+				/*
+				 * If this table was recognized as temporary, it means that we
+				 * found it because backend's temporary namespace was specified
+				 * in search_path. Thus, MyTempNamespace must contain valid oid.
+				 */
+				Assert(OidIsValid(namespaceId));
 			}
+
+			if (missing_ok && !OidIsValid(namespaceId))
+				relId = InvalidOid;
+			else
+				relId = get_relname_relid(relation->relname, namespaceId);
 		}
 		else if (relation->schemaname)
 		{
@@ -3620,21 +3636,19 @@ get_namespace_oid(const char *nspname, bool missing_ok)
 RangeVar *
 makeRangeVarFromNameList(const List *names)
 {
-	RangeVar   *rel = makeRangeVar(NULL, NULL, -1);
+	RangeVar   *rel;
 
 	switch (list_length(names))
 	{
 		case 1:
-			rel->relname = strVal(linitial(names));
+			rel = makeRangeVar(NULL, strVal(linitial(names)), -1);
 			break;
 		case 2:
-			rel->schemaname = strVal(linitial(names));
-			rel->relname = strVal(lsecond(names));
+			rel = makeRangeVar(strVal(linitial(names)), strVal(lsecond(names)), -1);
 			break;
 		case 3:
+			rel = makeRangeVar(strVal(lsecond(names)), strVal(lthird(names)), -1);
 			rel->catalogname = strVal(linitial(names));
-			rel->schemaname = strVal(lsecond(names));
-			rel->relname = strVal(lthird(names));
 			break;
 		default:
 			ereport(ERROR,
@@ -3841,6 +3855,8 @@ GetTempNamespaceProcNumber(Oid namespaceId)
 		return INVALID_PROC_NUMBER; /* no such namespace? */
 	if (strncmp(nspname, "pg_temp_", 8) == 0)
 		result = atoi(nspname + 8);
+	else if (strcmp(nspname, "pg_temp") == 0)
+		result = MyProcNumber;
 	else if (strncmp(nspname, "pg_toast_temp_", 14) == 0)
 		result = atoi(nspname + 14);
 	else
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index fc89352b661..aa4a80f3f29 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -1624,7 +1624,8 @@ RemoveRelations(DropStmt *drop)
 		state.heapOid = InvalidOid;
 		state.partParentOid = InvalidOid;
 
-		relOid = RangeVarGetRelidExtended(rel, lockmode, RVR_MISSING_OK,
+		relOid = RangeVarGetRelidExtended(rel, lockmode,
+										  RVR_MISSING_OK | RVR_OTHER_TEMP_OK,
 										  RangeVarCallbackForDropRelation,
 										  &state);
 
diff --git a/src/backend/nodes/makefuncs.c b/src/backend/nodes/makefuncs.c
index e2d9e9be41a..62edf24b5c2 100644
--- a/src/backend/nodes/makefuncs.c
+++ b/src/backend/nodes/makefuncs.c
@@ -478,10 +478,14 @@ makeRangeVar(char *schemaname, char *relname, int location)
 	r->schemaname = schemaname;
 	r->relname = relname;
 	r->inh = true;
-	r->relpersistence = RELPERSISTENCE_PERMANENT;
 	r->alias = NULL;
 	r->location = location;
 
+	if (r->schemaname && strncmp(r->schemaname, "pg_temp", 7) == 0)
+		r->relpersistence = RELPERSISTENCE_TEMP;
+	else
+		r->relpersistence = RELPERSISTENCE_PERMANENT;
+
 	return r;
 }
 
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 9fd48acb1f8..36f2f44cabe 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -19406,7 +19406,11 @@ makeRangeVarFromAnyName(List *names, int position, core_yyscan_t yyscanner)
 			break;
 	}
 
-	r->relpersistence = RELPERSISTENCE_PERMANENT;
+	if (r->schemaname && strncmp(r->schemaname, "pg_temp", 7) == 0)
+		r->relpersistence = RELPERSISTENCE_TEMP;
+	else
+		r->relpersistence = RELPERSISTENCE_PERMANENT;
+
 	r->location = position;
 
 	return r;
@@ -19446,6 +19450,11 @@ makeRangeVarFromQualifiedName(char *name, List *namelist, int location,
 			break;
 	}
 
+	if (r->schemaname && strncmp(r->schemaname, "pg_temp", 7) == 0)
+		r->relpersistence = RELPERSISTENCE_TEMP;
+	else
+		r->relpersistence = RELPERSISTENCE_PERMANENT;
+
 	return r;
 }
 
diff --git a/src/include/catalog/namespace.h b/src/include/catalog/namespace.h
index f1423f28c32..b08d55f2c97 100644
--- a/src/include/catalog/namespace.h
+++ b/src/include/catalog/namespace.h
@@ -90,6 +90,8 @@ typedef enum RVROption
 	RVR_MISSING_OK = 1 << 0,	/* don't error if relation doesn't exist */
 	RVR_NOWAIT = 1 << 1,		/* error if relation cannot be locked */
 	RVR_SKIP_LOCKED = 1 << 2,	/* skip if relation cannot be locked */
+	RVR_OTHER_TEMP_OK = 1 << 3	/* don't error if relation is temp relation of
+								   other session (needed for DROP command) */
 }			RVROption;
 
 typedef void (*RangeVarGetRelidCallback) (const RangeVar *relation, Oid relId,
-- 
2.43.0