netdev - [PATCH][net-next] net: check extack.

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Message-Id: <1533282321-17808-1-git-send-email-lirongqing@baidu.com>
Date:   Fri,  3 Aug 2018 15:45:21 +0800
From:   Li RongQing <lirongqing@...du.com>
To:     netdev@...r.kernel.org
Subject: [PATCH][net-next] net: check extack._msg before print

dev_set_mtu_ext is able to fail with a valid mtu value, at that
condition, extack._msg is not set and random since it is in stack,
then kernel will crash when print it.

Fixes: 7a4c53bee3324a ("net: report invalid mtu value via netlink extack")
Signed-off-by: Zhang Yu <zhangyu31@...du.com>
Signed-off-by: Li RongQing <lirongqing@...du.com>
---
 net/core/dev.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 36e994519488..f68122f0ab02 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -7583,8 +7583,9 @@ int dev_set_mtu(struct net_device *dev, int new_mtu)
 	struct netlink_ext_ack extack;
 	int err;
 
+	memset(&extack, 0, sizeof(extack));
 	err = dev_set_mtu_ext(dev, new_mtu, &extack);
-	if (err)
+	if (err && extack._msg)
 		net_err_ratelimited("%s: %s\n", dev->name, extack._msg);
 	return err;
 }
-- 
2.16.2