Prevent underflow in KeepLogSeg().

nathan-bossart · nathan-bossart · commit 137003036972 · 2023-04-27T14:32:40.000-07:00
The call to XLogGetReplicationSlotMinimumLSN() might return a greater LSN than the one given to the function. Subsequent segment number calculations might then underflow, which could result in unexpected behavior when removing or recyling WAL files. This was introduced with max_slot_wal_keep_size in c655077. To fix, skip the block of code for replication slots if the LSN is greater. Reported-by: Xu Xingwang Author: Kyotaro Horiguchi Reviewed-by: Junwang Zhao Discussion: https://postgr.es/m/17903-4288d439dee856c6%40postgresql.org Backpatch-through: 13
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
@@ -10037,7 +10037,7 @@ KeepLogSeg(XLogRecPtr recptr, XLogSegNo *logSegNo)
 	 * max_slot_wal_keep_size.
 	 */
 	keep = XLogGetReplicationSlotMinimumLSN();
-	if (keep != InvalidXLogRecPtr)
+	if (keep != InvalidXLogRecPtr && keep < recptr)
 	{
 		XLByteToSeg(keep, segno, wal_segment_size);
 

Original file line number	Diff line number	Diff line change
`@@ -10037,7 +10037,7 @@ KeepLogSeg(XLogRecPtr recptr, XLogSegNo *logSegNo)`
`10037`	`10037`	`* max_slot_wal_keep_size.`
`10038`	`10038`	`*/`
`10039`	`10039`	`keep = XLogGetReplicationSlotMinimumLSN();`
`10040`		`- if (keep != InvalidXLogRecPtr)`
	`10040`	`+ if (keep != InvalidXLogRecPtr && keep < recptr)`
`10041`	`10041`	`{`
`10042`	`10042`	`XLByteToSeg(keep, segno, wal_segment_size);`
`10043`	`10043`