From: Robert Haas <rhaas@postgresql.org>
Date: Thu, 6 Aug 2015 17:25:45 +0000 (-0400)
Subject: Fix incorrect calculation in shm_mq_receive.
X-Git-Tag: REL9_4_5~99
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=e72f2115ef6d574c64f42ea8b4cbe96accee08b2;p=postgresql

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
---

diff --git a/src/backend/storage/ipc/shm_mq.c b/src/backend/storage/ipc/shm_mq.c
index d96627a774..a49bd17fee 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;