From 8b8c5c4154f581c5d79585017443dffc1602bdf6 Mon Sep 17 00:00:00 2001
From: Stefan Metzmacher <metze@samba.org>
Date: Mon, 8 Jun 2020 12:23:47 +0200
Subject: [PATCH] s3:smbd: force multi-channel to be turned off without
 FreeBSD/Linux support
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For now it's safer to disable multi-channel without having support
for TIOCOUTQ/FIONWRITE on tcp sockets.

Using a fixed retransmission timeout (rto) of 1 second would be ok,
but we better require kernel support for requesting for unacked bytes
in the kernel send queue.

"force:server multi channel support = yes" can be used to overwrite
the compile time restriction (mainly for testing).

BUG: https://bugzilla.samba.org/show_bug.cgi?id=11897

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Günther Deschner <gd@samba.org>
---
 .../protocol/servermultichannelsupport.xml    |  5 ++++
 source3/smbd/globals.h                        |  2 ++
 source3/smbd/smb2_server.c                    | 26 +++++++++++++++++++
 source3/smbd/smbXsrv_client.c                 |  3 ++-
 4 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/docs-xml/smbdotconf/protocol/servermultichannelsupport.xml b/docs-xml/smbdotconf/protocol/servermultichannelsupport.xml
index e39785427a6..5f87298b4bd 100644
--- a/docs-xml/smbdotconf/protocol/servermultichannelsupport.xml
+++ b/docs-xml/smbdotconf/protocol/servermultichannelsupport.xml
@@ -15,6 +15,11 @@
     it may result in data corruption under some race conditions.
     Future releases may improve this situation.
     </para>
+
+    <para>Due to dependencies to kernel APIs of Linux or FreeBSD, it's only possible
+    to use this feature on Linux and FreeBSD for now. For testing this restriction
+    can be overwritten by specifying <constant>force:server multi channel support=yes</constant>
+    in addition.</para>
 </description>
 
 <value type="default">no</value>
diff --git a/source3/smbd/globals.h b/source3/smbd/globals.h
index 1276ffa0084..176c9053f3a 100644
--- a/source3/smbd/globals.h
+++ b/source3/smbd/globals.h
@@ -250,6 +250,8 @@ NTSTATUS smbd_smb2_process_negprot(struct smbXsrv_connection *xconn,
 
 DATA_BLOB smbd_smb2_generate_outbody(struct smbd_smb2_request *req, size_t size);
 
+bool smbXsrv_server_multi_channel_enabled(void);
+
 NTSTATUS smbd_smb2_request_error_ex(struct smbd_smb2_request *req,
 				    NTSTATUS status,
 				    DATA_BLOB *info,
diff --git a/source3/smbd/smb2_server.c b/source3/smbd/smb2_server.c
index 31a5a5f868c..a147f858c91 100644
--- a/source3/smbd/smb2_server.c
+++ b/source3/smbd/smb2_server.c
@@ -37,9 +37,11 @@
 /* SIOCOUTQ TIOCOUTQ are the same */
 #define __IOCTL_SEND_QUEUE_SIZE_OPCODE TIOCOUTQ
 #define __HAVE_TCP_INFO_RTO 1
+#define __ALLOW_MULTI_CHANNEL_SUPPORT 1
 #elif defined(FREEBSD)
 #define __IOCTL_SEND_QUEUE_SIZE_OPCODE FIONWRITE
 #define __HAVE_TCP_INFO_RTO 1
+#define __ALLOW_MULTI_CHANNEL_SUPPORT 1
 #endif
 
 #include "lib/crypto/gnutls_helpers.h"
@@ -1116,6 +1118,30 @@ static NTSTATUS smbd_smb2_request_setup_out(struct smbd_smb2_request *req)
 	return NT_STATUS_OK;
 }
 
+bool smbXsrv_server_multi_channel_enabled(void)
+{
+	bool enabled = lp_server_multi_channel_support();
+#ifndef __ALLOW_MULTI_CHANNEL_SUPPORT
+	bool forced = false;
+	/*
+	 * If we don't have support from the kernel
+	 * to ask for the un-acked number of bytes
+	 * in the socket send queue, we better
+	 * don't support multi-channel.
+	 */
+	forced = lp_parm_bool(-1, "force", "server multi channel support", false);
+	if (enabled && !forced) {
+		D_NOTICE("'server multi channel support' enabled "
+			 "but not supported on %s (%s)\n",
+			 SYSTEM_UNAME_SYSNAME, SYSTEM_UNAME_RELEASE);
+		DEBUGADD(DBGLVL_NOTICE, ("Please report this on "
+			"https://bugzilla.samba.org/show_bug.cgi?id=11897\n"));
+		enabled = false;
+	}
+#endif /* ! __ALLOW_MULTI_CHANNEL_SUPPORT */
+	return enabled;
+}
+
 static NTSTATUS smbXsrv_connection_get_rto_usecs(struct smbXsrv_connection *xconn,
 						 uint32_t *_rto_usecs)
 {
diff --git a/source3/smbd/smbXsrv_client.c b/source3/smbd/smbXsrv_client.c
index c6114d4b8dc..f61ab3da35b 100644
--- a/source3/smbd/smbXsrv_client.c
+++ b/source3/smbd/smbXsrv_client.c
@@ -522,7 +522,8 @@ NTSTATUS smbXsrv_client_create(TALLOC_CTX *mem_ctx,
 	client->raw_ev_ctx = ev_ctx;
 	client->msg_ctx = msg_ctx;
 
-	client->server_multi_channel_enabled = lp_server_multi_channel_support();
+	client->server_multi_channel_enabled =
+		smbXsrv_server_multi_channel_enabled();
 	if (client->server_multi_channel_enabled) {
 		client->next_channel_id = 1;
 	}
-- 
2.34.1