From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sun, 20 Dec 2020 17:38:32 +0000 (-0500)
Subject: Avoid memcpy() with same source and destination in pgstat_recv_replslot.
X-Git-Tag: REL_14_BETA1~1108
X-Git-Url: http://git.postgresql.org/gitweb/?a=commitdiff_plain;h=ed6329cfa975a13c58c44676464585cda5d317b3;p=postgresql.git

Avoid memcpy() with same source and destination in pgstat_recv_replslot.

Same type of issue as in commit 53d4f5fef and earlier fixes; also
found by apparently-more-picky-than-the-buildfarm valgrind testing.
This one is an oversight in commit 986816750.  Since that's new in
HEAD, no need for a back-patch.
---

diff --git a/src/backend/postmaster/pgstat.c b/src/backend/postmaster/pgstat.c
index 6b60f293e94..d87d9d06ee2 100644
--- a/src/backend/postmaster/pgstat.c
+++ b/src/backend/postmaster/pgstat.c
@@ -6916,15 +6916,15 @@ pgstat_recv_replslot(PgStat_MsgReplSlot *msg, int len)
 		return;
 
 	/* it must be a valid replication slot index */
-	Assert(idx >= 0 && idx < max_replication_slots);
+	Assert(idx < nReplSlotStats);
 
 	if (msg->m_drop)
 	{
 		/* Remove the replication slot statistics with the given name */
-		memcpy(&replSlotStats[idx], &replSlotStats[nReplSlotStats - 1],
-			   sizeof(PgStat_ReplSlotStats));
+		if (idx < nReplSlotStats - 1)
+			memcpy(&replSlotStats[idx], &replSlotStats[nReplSlotStats - 1],
+				   sizeof(PgStat_ReplSlotStats));
 		nReplSlotStats--;
-		Assert(nReplSlotStats >= 0);
 	}
 	else
 	{