linux-kernel - [PATCH 3.16 180/204] vlan: fix a use-after-free in vlan_device

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Date:   Thu, 28 Dec 2017 17:05:44 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Linus Torvalds" <torvalds@...ux-foundation.org>,
        "Alexander Duyck" <alexander.duyck@...il.com>,
        "Girish Moodalbail" <girish.moodalbail@...cle.com>,
        "Cong Wang" <xiyou.wangcong@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        "Fengguang Wu" <fengguang.wu@...el.com>
Subject: [PATCH 3.16 180/204] vlan: fix a use-after-free in
 vlan_device_event()

3.16.52-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Cong Wang <xiyou.wangcong@...il.com>

commit 052d41c01b3a2e3371d66de569717353af489d63 upstream.

After refcnt reaches zero, vlan_vid_del() could free
dev->vlan_info via RCU:

	RCU_INIT_POINTER(dev->vlan_info, NULL);
	call_rcu(&vlan_info->rcu, vlan_info_rcu_free);

However, the pointer 'grp' still points to that memory
since it is set before vlan_vid_del():

        vlan_info = rtnl_dereference(dev->vlan_info);
        if (!vlan_info)
                goto out;
        grp = &vlan_info->grp;

Depends on when that RCU callback is scheduled, we could
trigger a use-after-free in vlan_group_for_each_dev()
right following this vlan_vid_del().

Fix it by moving vlan_vid_del() before setting grp. This
is also symmetric to the vlan_vid_add() we call in
vlan_device_event().

Reported-by: Fengguang Wu <fengguang.wu@...el.com>
Fixes: efc73f4bbc23 ("net: Fix memory leak - vlan_info struct")
Cc: Alexander Duyck <alexander.duyck@...il.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Girish Moodalbail <girish.moodalbail@...cle.com>
Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
Reviewed-by: Girish Moodalbail <girish.moodalbail@...cle.com>
Tested-by: Fengguang Wu <fengguang.wu@...el.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 net/8021q/vlan.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/net/8021q/vlan.c
+++ b/net/8021q/vlan.c
@@ -364,6 +364,9 @@ static int vlan_device_event(struct noti
 			dev->name);
 		vlan_vid_add(dev, htons(ETH_P_8021Q), 0);
 	}
+	if (event == NETDEV_DOWN &&
+	    (dev->features & NETIF_F_HW_VLAN_CTAG_FILTER))
+		vlan_vid_del(dev, htons(ETH_P_8021Q), 0);
 
 	vlan_info = rtnl_dereference(dev->vlan_info);
 	if (!vlan_info)
@@ -408,9 +411,6 @@ static int vlan_device_event(struct noti
 		break;
 
 	case NETDEV_DOWN:
-		if (dev->features & NETIF_F_HW_VLAN_CTAG_FILTER)
-			vlan_vid_del(dev, htons(ETH_P_8021Q), 0);
-
 		/* Put all VLANs for this dev in the down state too.  */
 		vlan_group_for_each_dev(grp, i, vlandev) {
 			flgs = vlandev->flags;