From: Robert Haas <rhaas@postgresql.org>
Date: Fri, 1 Jul 2016 12:51:58 +0000 (-0400)
Subject: Fix crash bug in RestoreSnapshot.
X-Git-Tag: REL9_5_4~66
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=8f4a369c28be28351ce64e12ac895db515dd5916;p=postgresql

Fix crash bug in RestoreSnapshot.

If serialized_snapshot->subxcnt > 0 and serialized_snapshot->xcnt == 0,
the old coding would do the wrong thing and crash.  This can happen
on standby servers.

Report by Andreas Seltenreich.  Patch by Thomas Munro, reviewed by
Amit Kapila and tested by Andreas Seltenreich.
---

diff --git a/src/backend/utils/time/snapmgr.c b/src/backend/utils/time/snapmgr.c
index 6ef2df8a20..9cbe226b22 100644
--- a/src/backend/utils/time/snapmgr.c
+++ b/src/backend/utils/time/snapmgr.c
@@ -1573,7 +1573,8 @@ RestoreSnapshot(char *start_address)
 	/* Copy SubXIDs, if present. */
 	if (serialized_snapshot->subxcnt > 0)
 	{
-		snapshot->subxip = snapshot->xip + serialized_snapshot->xcnt;
+		snapshot->subxip = ((TransactionId *) (snapshot + 1)) +
+			serialized_snapshot->xcnt;
 		memcpy(snapshot->subxip, serialized_xids + serialized_snapshot->xcnt,
 			   serialized_snapshot->subxcnt * sizeof(TransactionId));
 	}