[PATCH net-next] net: tipc: fix FB_MTU eat two pages

[menglong8 . dong]

From: Menglong Dong <dong.menglong@xxxxxxxxxx>

FB_MTU is used in 'tipc_msg_build()' to alloc smaller skb when memory
allocation fails, which can avoid unnecessary sending failures.

The value of FB_MTU now is 3744, and the data size will be:

  (3744 + SKB_DATA_ALIGN(sizeof(struct skb_shared_info)) + \
    SKB_DATA_ALIGN(BUF_HEADROOM + BUF_TAILROOM + 3))

which is larger than one page(4096), and two pages will be allocated.

To avoid it, replace '3744' with a calculation:

FB_MTU = (PAGE_SIZE - SKB_DATA_ALIGN(sizeof(struct skb_shared_info))
          - SKB_DATA_ALIGN(BUF_HEADROOM + BUF_TAILROOM + 3))

Fixes: 4c94cc2d3d57 ("tipc: fall back to smaller MTU if allocation of local send skb fails")

Reported-by: Zeal Robot <zealci@xxxxxxxxxx>
Signed-off-by: Menglong Dong <dong.menglong@xxxxxxxxxx>
---
 net/tipc/bcast.c |  1 +
 net/tipc/msg.c   |  8 +------
 net/tipc/msg.h   |  1 -
 net/tipc/mtu.h   | 55 ++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 57 insertions(+), 8 deletions(-)
 create mode 100644 net/tipc/mtu.h

diff --git a/net/tipc/bcast.c b/net/tipc/bcast.c
index d4beca895992..c641b68e0812 100644
--- a/net/tipc/bcast.c
+++ b/net/tipc/bcast.c
@@ -41,6 +41,7 @@
 #include "bcast.h"
 #include "link.h"
 #include "name_table.h"
+#include "mtu.h"
 
 #define BCLINK_WIN_DEFAULT  50	/* bcast link window size (default) */
 #define BCLINK_WIN_MIN      32	/* bcast minimum link window size */
diff --git a/net/tipc/msg.c b/net/tipc/msg.c
index ce6ab54822d8..ec70d271c2da 100644
--- a/net/tipc/msg.c
+++ b/net/tipc/msg.c
@@ -40,15 +40,9 @@
 #include "addr.h"
 #include "name_table.h"
 #include "crypto.h"
+#include "mtu.h"
 
 #define MAX_FORWARD_SIZE 1024
-#ifdef CONFIG_TIPC_CRYPTO
-#define BUF_HEADROOM ALIGN(((LL_MAX_HEADER + 48) + EHDR_MAX_SIZE), 16)
-#define BUF_TAILROOM (TIPC_AES_GCM_TAG_SIZE)
-#else
-#define BUF_HEADROOM (LL_MAX_HEADER + 48)
-#define BUF_TAILROOM 16
-#endif
 
 static unsigned int align(unsigned int i)
 {
diff --git a/net/tipc/msg.h b/net/tipc/msg.h
index 5d64596ba987..e83689d0f0f6 100644
--- a/net/tipc/msg.h
+++ b/net/tipc/msg.h
@@ -99,7 +99,6 @@ struct plist;
 #define MAX_H_SIZE                60	/* Largest possible TIPC header size */
 
 #define MAX_MSG_SIZE (MAX_H_SIZE + TIPC_MAX_USER_MSG_SIZE)
-#define FB_MTU                  3744
 #define TIPC_MEDIA_INFO_OFFSET	5
 
 struct tipc_skb_cb {
diff --git a/net/tipc/mtu.h b/net/tipc/mtu.h
new file mode 100644
index 000000000000..033f0b178f9d
--- /dev/null
+++ b/net/tipc/mtu.h
@@ -0,0 +1,55 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright 2021 ZTE Corporation.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the names of the copyright holders nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * Alternatively, this software may be distributed under the terms of the
+ * GNU General Public License ("GPL") version 2 as published by the Free
+ * Software Foundation.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef _TIPC_MTU_H
+#define _TIPC_MTU_H
+
+#include <linux/tipc.h>
+#include "crypto.h"
+
+#ifdef CONFIG_TIPC_CRYPTO
+#define BUF_HEADROOM ALIGN(((LL_MAX_HEADER + 48) + EHDR_MAX_SIZE), 16)
+#define BUF_TAILROOM (TIPC_AES_GCM_TAG_SIZE)
+#define FB_MTU	(PAGE_SIZE - \
+		 SKB_DATA_ALIGN(sizeof(struct skb_shared_info)) - \
+		 SKB_DATA_ALIGN(BUF_HEADROOM + BUF_TAILROOM + 3))
+#else
+#define BUF_HEADROOM (LL_MAX_HEADER + 48)
+#define BUF_TAILROOM 16
+#define FB_MTU	(PAGE_SIZE - \
+		 SKB_DATA_ALIGN(sizeof(struct skb_shared_info)) - \
+		 SKB_DATA_ALIGN(BUF_HEADROOM + 3))
+#endif
+
+#endif
-- 
2.25.1