From e72f2115ef6d574c64f42ea8b4cbe96accee08b2 Mon Sep 17 00:00:00 2001
From: Robert Haas <rhaas@postgresql.org>
Date: Thu, 6 Aug 2015 13:25:45 -0400
Subject: [PATCH] Fix incorrect calculation in shm_mq_receive.

If some, but not all, of the length word has already been read, and the
next attempt to read sees exactly the number of bytes needed to complete
the length word, or fewer, then we'll incorrectly read less than all of
the available data.

Antonin Houska
---
 src/backend/storage/ipc/shm_mq.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/backend/storage/ipc/shm_mq.c b/src/backend/storage/ipc/shm_mq.c
index d96627a774e..a49bd17feeb 100644
--- a/src/backend/storage/ipc/shm_mq.c
+++ b/src/backend/storage/ipc/shm_mq.c
@@ -488,7 +488,7 @@ shm_mq_receive(shm_mq_handle *mqh, Size *nbytesp, void **datap, bool nowait)
 			if (mqh->mqh_partial_bytes + rb > sizeof(Size))
 				lengthbytes = sizeof(Size) - mqh->mqh_partial_bytes;
 			else
-				lengthbytes = rb - mqh->mqh_partial_bytes;
+				lengthbytes = rb;
 			memcpy(&mqh->mqh_buffer[mqh->mqh_partial_bytes], rawdata,
 				   lengthbytes);
 			mqh->mqh_partial_bytes += lengthbytes;
-- 
GitLab