netdev - [PATCH] netvsc: fix use-after-free in netvsc_change

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Message-ID: <MWHPR03MB266949159A2BCA01B5EBB778BF280@MWHPR03MB2669.namprd03.prod.outlook.com>
Date:   Thu, 2 Mar 2017 13:00:53 +0000
From:   Dexuan Cui <decui@...rosoft.com>
To:     David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "driverdev-devel@...uxdriverproject.org" 
        <driverdev-devel@...uxdriverproject.org>
Subject: [PATCH] netvsc: fix use-after-free in netvsc_change_mtu()

'nvdev' is freed in rndis_filter_device_remove -> netvsc_device_remove ->
free_netvsc_device, so we mustn't access it, before it's re-created in
rndis_filter_device_add -> netvsc_device_add.

Signed-off-by: Dexuan Cui <decui@...rosoft.com>
Cc: "K. Y. Srinivasan" <kys@...rosoft.com>
Cc: Haiyang Zhang <haiyangz@...rosoft.com>
Cc: Stephen Hemminger <sthemmin@...rosoft.com>
---
 drivers/net/hyperv/netvsc_drv.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/drivers/net/hyperv/netvsc_drv.c b/drivers/net/hyperv/netvsc_drv.c
index 2d3cdb0..bc05c89 100644
--- a/drivers/net/hyperv/netvsc_drv.c
+++ b/drivers/net/hyperv/netvsc_drv.c
@@ -859,15 +859,22 @@ static int netvsc_change_mtu(struct net_device *ndev, int mtu)
 	if (ret)
 		goto out;
 
+	memset(&device_info, 0, sizeof(device_info));
+	device_info.ring_size = ring_size;
+	device_info.num_chn = nvdev->num_chn;
+	device_info.max_num_vrss_chns = nvdev->num_chn;
+
 	ndevctx->start_remove = true;
 	rndis_filter_device_remove(hdev, nvdev);
 
+	/* 'nvdev' has been freed in rndis_filter_device_remove() ->
+	 * netvsc_device_remove () -> free_netvsc_device().
+	 * We mustn't access it before it's re-created in
+	 * rndis_filter_device_add() -> netvsc_device_add().
+	 */
+
 	ndev->mtu = mtu;
 
-	memset(&device_info, 0, sizeof(device_info));
-	device_info.ring_size = ring_size;
-	device_info.num_chn = nvdev->num_chn;
-	device_info.max_num_vrss_chns = nvdev->num_chn;
 	rndis_filter_device_add(hdev, &device_info);
 
 out:
-- 
2.7.4