From 4448b3a2a99a520fdc7fc06c4a72ea2a84b863b5 Mon Sep 17 00:00:00 2001
From: Robin Gareus <robin@gareus.org>
Date: Sun, 20 Nov 2022 15:01:08 +0100
Subject: [PATCH] Prevent crash when running unconfigured meter processor

If Route::configure_processors fails at session start,
meters are not configured (#9106), leading to a crash when
::run() is called (insufficient peak/max/midi buffers).
---
 libs/ardour/ardour/meter.h |  1 +
 libs/ardour/meter.cc       | 19 +++++++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/libs/ardour/ardour/meter.h b/libs/ardour/ardour/meter.h
index b6fb104a34..036c206764 100644
--- a/libs/ardour/ardour/meter.h
+++ b/libs/ardour/ardour/meter.h
@@ -99,6 +99,7 @@ private:
 	 *  as it can be altered outside a \ref configure_io by \ref reflect_inputs .
 	 */
 	ChanCount current_meters;
+	ChanCount _max_n_meters;
 
 	GATOMIC_QUAL gint _reset_dpm;
 	GATOMIC_QUAL gint _reset_max;
diff --git a/libs/ardour/meter.cc b/libs/ardour/meter.cc
index 435d00d8cf..763cd74d09 100644
--- a/libs/ardour/meter.cc
+++ b/libs/ardour/meter.cc
@@ -269,6 +269,23 @@ PeakMeter::configure_io (ChanCount in, ChanCount out)
 void
 PeakMeter::reflect_inputs (const ChanCount& in)
 {
+	if (!_configured || in > _max_n_meters) {
+		/* meter has to be configured at least once, and
+		 * Route has to call ::set_max_channels after successful
+		 * configure_processors.
+		 */
+		return;
+	}
+
+	/* In theory this cannot happen. After an initial successful
+	 * configuration, Route::configure_processors_unlocked will revert
+	 * to a prior config in case of an error.
+	 */
+	assert (in <= _max_n_meters);
+	if (in > _max_n_meters) {
+		return;
+	}
+
 	reset ();
 	current_meters = in;
 	reset_max ();
@@ -283,6 +300,8 @@ PeakMeter::emit_configuration_changed ()
 void
 PeakMeter::set_max_channels (const ChanCount& chn)
 {
+	_max_n_meters = chn;
+
 	uint32_t const limit   = chn.n_total ();
 	const size_t   n_audio = chn.n_audio ();