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

tglsfdc · tglsfdc · commit ed6329cfa975 · 2020-12-20T12:38:32.000-05:00
Same type of issue as in commit 53d4f5f and earlier fixes; also found by apparently-more-picky-than-the-buildfarm valgrind testing. This one is an oversight in commit 9868167. 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
@@ -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
 	{

Original file line number	Diff line number	Diff line change
`@@ -6916,15 +6916,15 @@ pgstat_recv_replslot(PgStat_MsgReplSlot *msg, int len)`
`6916`	`6916`	`return;`
`6917`	`6917`
`6918`	`6918`	`/* it must be a valid replication slot index */`
`6919`		`- Assert(idx >= 0 && idx < max_replication_slots);`
	`6919`	`+ Assert(idx < nReplSlotStats);`
`6920`	`6920`
`6921`	`6921`	`if (msg->m_drop)`
`6922`	`6922`	`{`
`6923`	`6923`	`/* Remove the replication slot statistics with the given name */`
`6924`		`- memcpy(&replSlotStats[idx], &replSlotStats[nReplSlotStats - 1],`
`6925`		`- sizeof(PgStat_ReplSlotStats));`
	`6924`	`+ if (idx < nReplSlotStats - 1)`
	`6925`	`+ memcpy(&replSlotStats[idx], &replSlotStats[nReplSlotStats - 1],`
	`6926`	`+ sizeof(PgStat_ReplSlotStats));`
`6926`	`6927`	`nReplSlotStats--;`
`6927`		`- Assert(nReplSlotStats >= 0);`
`6928`	`6928`	`}`
`6929`	`6929`	`else`
`6930`	`6930`	`{`