From 285e75b3b08c8889ebc7a077da654065561d8369 Mon Sep 17 00:00:00 2001
From: Artem Boldariev <artem@boldariev.com>
Date: Fri, 2 Jun 2023 14:28:50 +0300
Subject: [PATCH 1/2] Use appropriately sized send buffers for DNS messages
 over TCP

This commit changes send buffers allocation strategy for stream based
transports. Before that change we would allocate a dynamic buffers
sized at 64Kb even when we do not need that much. That could lead to
high memory usage on server. Now we resize the send buffer to match
the size of the actual data, freeing the memory at the end of the
buffer for being reused later.

(cherry picked from commit d8a5feb5567aaebcc11c5b20b9b667c040c4d22a)
---
 lib/ns/client.c            | 24 +++++++++++++++---------
 lib/ns/include/ns/client.h |  1 +
 2 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/lib/ns/client.c b/lib/ns/client.c
index 368a9fd77f..5196a74892 100644
--- a/lib/ns/client.c
+++ b/lib/ns/client.c
@@ -348,6 +348,7 @@ client_allocsendbuf(ns_client_t *client, isc_buffer_t *buffer,
 		INSIST(client->tcpbuf == NULL);
 		client->tcpbuf = isc_mem_get(client->mctx,
 					     NS_CLIENT_TCP_BUFFER_SIZE);
+		client->tcpbuf_size = NS_CLIENT_TCP_BUFFER_SIZE;
 		data = client->tcpbuf;
 		isc_buffer_init(buffer, data, NS_CLIENT_TCP_BUFFER_SIZE);
 	} else {
@@ -380,7 +381,17 @@ client_sendpkg(ns_client_t *client, isc_buffer_t *buffer) {
 
 	REQUIRE(client->sendhandle == NULL);
 
-	isc_buffer_usedregion(buffer, &r);
+	if (isc_buffer_base(buffer) == client->tcpbuf) {
+		size_t used = isc_buffer_usedlength(buffer);
+		client->tcpbuf = isc_mem_reget(client->manager->mctx,
+					       client->tcpbuf,
+					       client->tcpbuf_size, used);
+		client->tcpbuf_size = used;
+		r.base = client->tcpbuf;
+		r.length = used;
+	} else {
+		isc_buffer_usedregion(buffer, &r);
+	}
 	isc_nmhandle_attach(client->handle, &client->sendhandle);
 
 	if (isc_nm_is_http_handle(client->handle)) {
@@ -450,9 +461,7 @@ ns_client_sendraw(ns_client_t *client, dns_message_t *message) {
 	return;
 done:
 	if (client->tcpbuf != NULL) {
-		isc_mem_put(client->mctx, client->tcpbuf,
-			    NS_CLIENT_TCP_BUFFER_SIZE);
-		client->tcpbuf = NULL;
+		isc_mem_put(client->mctx, client->tcpbuf, client->tcpbuf_size);
 	}
 
 	ns_client_drop(client, result);
@@ -736,9 +745,7 @@ renderend:
 
 cleanup:
 	if (client->tcpbuf != NULL) {
-		isc_mem_put(client->mctx, client->tcpbuf,
-			    NS_CLIENT_TCP_BUFFER_SIZE);
-		client->tcpbuf = NULL;
+		isc_mem_put(client->mctx, client->tcpbuf, client->tcpbuf_size);
 	}
 
 	if (cleanup_cctx) {
@@ -1620,8 +1627,7 @@ ns__client_reset_cb(void *client0) {
 
 	ns_client_endrequest(client);
 	if (client->tcpbuf != NULL) {
-		isc_mem_put(client->mctx, client->tcpbuf,
-			    NS_CLIENT_TCP_BUFFER_SIZE);
+		isc_mem_put(client->mctx, client->tcpbuf, client->tcpbuf_size);
 	}
 
 	if (client->keytag != NULL) {
diff --git a/lib/ns/include/ns/client.h b/lib/ns/include/ns/client.h
index f9d694fdd1..6bd41d4e41 100644
--- a/lib/ns/include/ns/client.h
+++ b/lib/ns/include/ns/client.h
@@ -184,6 +184,7 @@ struct ns_client {
 	isc_nmhandle_t *prefetchhandle; /* Waiting for prefetch / rpzfetch */
 	isc_nmhandle_t *updatehandle;	/* Waiting for update callback */
 	unsigned char  *tcpbuf;
+	size_t		tcpbuf_size;
 	dns_message_t  *message;
 	unsigned char  *sendbuf;
 	dns_rdataset_t *opt;

From 2c145b186220ecf087bc8bbdbb881c872cc77201 Mon Sep 17 00:00:00 2001
From: Artem Boldariev <artem@boldariev.com>
Date: Fri, 2 Jun 2023 12:49:15 +0300
Subject: [PATCH 2/2] Update CHANGES and release note [GL #4038]

Mention that memory usage was reduced by allocating properly sized
send buffers for stream-based transports.

(cherry picked from commit 8672d5484759bac94d4457ab362604667bbb13c5)
---
 CHANGES                     | 4 ++++
 doc/notes/notes-current.rst | 4 ++++
 2 files changed, 8 insertions(+)

diff --git a/CHANGES b/CHANGES
index 47104d87e5..fe143c5fd1 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,3 +1,7 @@
+6188.	[performance]	Reduce memory consumption by allocating properly
+			sized send buffers for stream-based transports.
+			[GL #4038]
+
 6185.	[func]		Add "ClientQuota" statistics channel counter, which
 			indicates the number of the resolver's spilled queries
 			due to reaching the clients per query quota. [GL !7978]
diff --git a/doc/notes/notes-current.rst b/doc/notes/notes-current.rst
index adec5ced27..b4f461b3e0 100644
--- a/doc/notes/notes-current.rst
+++ b/doc/notes/notes-current.rst
@@ -48,6 +48,10 @@ Bug Fixes
   a delegation from cache was returned to the client. This has now been fixed.
   :gl:`#3950`
 
+- BIND could allocate too big buffers when sending data via
+  stream-based DNS transports, leading to increased memory usage.
+  This has been fixed. :gl:`#4038`
+
 Known Issues
 ~~~~~~~~~~~~