From: Thomas Munro <tmunro@postgresql.org>
Date: Thu, 26 Jan 2023 01:50:07 +0000 (+1300)
Subject: Fix rare sharedtuplestore.c corruption.
X-Git-Tag: REL_11_19~7
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=d95dcc9ab5f8816c7a4ac591628c68efaa2a9b7a;p=thirdparty%2Fpostgresql.git

Fix rare sharedtuplestore.c corruption.

If the final chunk of an oversized tuple being written out to disk was
exactly 32760 bytes, it would be corrupted due to a fencepost bug.

Bug #17619.  Back-patch to 11 where the code arrived.

While testing that (see test module in archives), I (tmunro) noticed
that the per-participant page counter was not initialized to zero as it
should have been; that wasn't a live bug when it was written since DSM
memory was originally always zeroed, but since 14
min_dynamic_shared_memory might be configured and it supplies non-zeroed
memory, so that is also fixed here.

Author: Dmitry Astapov <dastapov@gmail.com>
Discussion: https://postgr.es/m/17619-0de62ceda812b8b5%40postgresql.org
---

diff --git a/src/backend/utils/sort/sharedtuplestore.c b/src/backend/utils/sort/sharedtuplestore.c
index d2555c2c3ba..b9e801d6e11 100644
--- a/src/backend/utils/sort/sharedtuplestore.c
+++ b/src/backend/utils/sort/sharedtuplestore.c
@@ -160,6 +160,7 @@ sts_initialize(SharedTuplestore *sts, int participants,
 		LWLockInitialize(&sts->participants[i].lock,
 						 LWTRANCHE_SHARED_TUPLESTORE);
 		sts->participants[i].read_page = 0;
+		sts->participants[i].npages = 0;
 		sts->participants[i].writing = false;
 	}
 
@@ -321,7 +322,7 @@ sts_puttuple(SharedTuplestoreAccessor *accessor, void *meta_data,
 
 	/* Do we have space? */
 	size = accessor->sts->meta_data_size + tuple->t_len;
-	if (accessor->write_pointer + size >= accessor->write_end)
+	if (accessor->write_pointer + size > accessor->write_end)
 	{
 		if (accessor->write_chunk == NULL)
 		{
@@ -341,7 +342,7 @@ sts_puttuple(SharedTuplestoreAccessor *accessor, void *meta_data,
 		}
 
 		/* It may still not be enough in the case of a gigantic tuple. */
-		if (accessor->write_pointer + size >= accessor->write_end)
+		if (accessor->write_pointer + size > accessor->write_end)
 		{
 			size_t		written;