v16-0001-Prevent-access-to-other-sessions-temp-tables.patch

From 6b25b30bc981dd6420788014face14a13bb9461d Mon Sep 17 00:00:00 2001
From: Daniil Davidov <d.davydov@postgrespro.ru>
Date: Fri, 10 Apr 2026 13:51:14 +0700
Subject: [PATCH v16 1/2] Prevent access to other sessions' temp tables

---
 src/backend/storage/aio/read_stream.c | 10 ++++++++++
 src/backend/storage/buffer/bufmgr.c   | 17 +++++++++++++++--
 2 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/src/backend/storage/aio/read_stream.c b/src/backend/storage/aio/read_stream.c
index b6fce4e7cc6..213f6206ba2 100644
--- a/src/backend/storage/aio/read_stream.c
+++ b/src/backend/storage/aio/read_stream.c
@@ -776,6 +776,16 @@ read_stream_begin_impl(int flags,
 	uint32		max_possible_buffer_limit;
 	Oid			tablespace_id;
 
+	/*
+	 * Reject attempts to read non-local temporary relations; we would be
+	 * likely to get wrong data since we have no visibility into the owning
+	 * session's local buffers.
+	 */
+	if (rel && RELATION_IS_OTHER_TEMP(rel))
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("cannot access temporary relations of other sessions")));
+
 	/*
 	 * Decide how many I/Os we will allow to run at the same time.  That
 	 * currently means advice to the kernel to tell it that we will soon read.
diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index 3cc0b0bdd92..653278140fb 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -795,7 +795,7 @@ PrefetchBuffer(Relation reln, ForkNumber forkNum, BlockNumber blockNum)
 		if (RELATION_IS_OTHER_TEMP(reln))
 			ereport(ERROR,
 					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-					 errmsg("cannot access temporary tables of other sessions")));
+					 errmsg("cannot access temporary relations of other sessions")));
 
 		/* pass it off to localbuf.c */
 		return PrefetchLocalBuffer(RelationGetSmgr(reln), forkNum, blockNum);
@@ -936,7 +936,7 @@ ReadBufferExtended(Relation reln, ForkNumber forkNum, BlockNumber blockNum,
 	if (RELATION_IS_OTHER_TEMP(reln))
 		ereport(ERROR,
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-				 errmsg("cannot access temporary tables of other sessions")));
+				 errmsg("cannot access temporary relations of other sessions")));
 
 	/*
 	 * Read the buffer, and update pgstat counters to reflect a cache hit or
@@ -1317,6 +1317,12 @@ ReadBuffer_common(Relation rel, SMgrRelation smgr, char smgr_persistence,
 	else
 		persistence = smgr_persistence;
 
+	/* see comments in ReadBufferExtended */
+	if (rel != NULL && RELATION_IS_OTHER_TEMP(rel))
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("cannot access temporary relations of other sessions")));
+
 	if (unlikely(mode == RBM_ZERO_AND_CLEANUP_LOCK ||
 				 mode == RBM_ZERO_AND_LOCK))
 	{
@@ -1393,6 +1399,13 @@ StartReadBuffersImpl(ReadBuffersOperation *operation,
 		io_object = IOOBJECT_RELATION;
 	}
 
+
+	/* see comments in ReadBufferExtended */
+	if (operation->rel != NULL && RELATION_IS_OTHER_TEMP(operation->rel))
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("cannot access temporary relations of other sessions")));
+
 	for (int i = 0; i < actual_nblocks; ++i)
 	{
 		bool		found;
-- 
2.43.0