Restrict copying of invalidated replication slots.

Previously, invalidated logical and physical replication slots could
be copied using the pg_copy_logical_replication_slot and
pg_copy_physical_replication_slot functions. Replication slots that
were invalidated for reasons other than WAL removal retained their
restart_lsn. This meant that a new slot copied from an invalidated
slot could have a restart_lsn pointing to a WAL segment that might
have already been removed.

This commit restricts the copying of invalidated replication slots.

Backpatch to v16, where slots could retain their restart_lsn when
invalidated for reasons other than WAL removal.

For v15 and earlier, this check is not required since slots can only
be invalidated due to WAL removal, and existing checks already handle
this issue.

Author: Shlok Kyal <shlok.kyal.oss@gmail.com>
Reviewed-by: vignesh C <vignesh21@gmail.com>
Reviewed-by: Zhijie Hou <houzj.fnst@fujitsu.com>
Reviewed-by: Peter Smith <smithpb2250@gmail.com>
Reviewed-by: Masahiko Sawada <sawada.mshk@gmail.com>
Reviewed-by: Amit Kapila <amit.kapila16@gmail.com>
Discussion: https://postgr.es/m/CANhcyEU65aH0VYnLiu%3DOhNNxhnhNhwcXBeT-jvRe1OiJTo_Ayg%40mail.gmail.com
Backpatch-through: 16

2 files changed, 30 insertions, 0 deletions

diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 43c3cc7336b..01e98bc1cef 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -681,6 +681,13 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
 				 errmsg("cannot copy a replication slot that doesn't reserve WAL")));
 
+	/* Cannot copy an invalidated replication slot */
+	if (first_slot_contents.data.invalidated != RS_INVAL_NONE)
+		ereport(ERROR,
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("cannot copy invalidated replication slot \"%s\"",
+					   NameStr(*src_name)));
+
 	/* Overwrite params from optional arguments */
 	if (PG_NARGS() >= 3)
 		temporary = PG_GETARG_BOOL(2);
@@ -782,6 +789,20 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 							NameStr(*src_name)),
 					 errhint("Retry when the source replication slot's confirmed_flush_lsn is valid.")));
 
+		/*
+		 * Copying an invalid slot doesn't make sense. Note that the source
+		 * slot can become invalid after we create the new slot and copy the
+		 * data of source slot. This is possible because the operations in
+		 * InvalidateObsoleteReplicationSlots() are not serialized with this
+		 * function. Even though we can't detect such a case here, the copied
+		 * slot will become invalid in the next checkpoint cycle.
+		 */
+		if (second_slot_contents.data.invalidated != RS_INVAL_NONE)
+			ereport(ERROR,
+					errmsg("cannot copy replication slot \"%s\"",
+						   NameStr(*src_name)),
+					errdetail("The source replication slot was invalidated during the copy operation."));
+
 		/* Install copied values again */
 		SpinLockAcquire(&MyReplicationSlot->mutex);
 		MyReplicationSlot->effective_xmin = copy_effective_xmin;
diff --git a/src/test/recovery/t/035_standby_logical_decoding.pl b/src/test/recovery/t/035_standby_logical_decoding.pl
index aeb79f51e71..4eca17885d6 100644
--- a/src/test/recovery/t/035_standby_logical_decoding.pl
+++ b/src/test/recovery/t/035_standby_logical_decoding.pl
@@ -583,6 +583,15 @@ check_pg_recvlogical_stderr($handle,
 	"can no longer get changes from replication slot \"vacuum_full_activeslot\""
 );
 
+# Attempt to copy an invalidated logical replication slot
+($result, $stdout, $stderr) = $node_standby->psql(
+	'postgres',
+	qq[select pg_copy_logical_replication_slot('vacuum_full_inactiveslot', 'vacuum_full_inactiveslot_copy');],
+	replication => 'database');
+ok( $stderr =~
+	  /ERROR:  cannot copy invalidated replication slot "vacuum_full_inactiveslot"/,
+	"invalidated slot cannot be copied");
+
 # Turn hot_standby_feedback back on
 change_hot_standby_feedback_and_wait_for_xmins(1, 1);