Patch "vlan: fix a use-after-free in vlan_device_event()" has been added to the 3.18-stable tree

This is a note to let you know that I've just added the patch titled

vlan: fix a use-after-free in vlan_device_event()

to the 3.18-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
vlan-fix-a-use-after-free-in-vlan_device_event.patch
and it can be found in the queue-3.18 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Cong Wang <[email protected]>
Date: Thu, 9 Nov 2017 16:43:13 -0800
Subject: vlan: fix a use-after-free in vlan_device_event()

From: Cong Wang <[email protected]>

[ Upstream commit 052d41c01b3a2e3371d66de569717353af489d63 ]

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().

---
 net/8021q/vlan.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

@@ -376,6 +376,9 @@ 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)

@@ -420,9 +423,6 @@ 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;

Patches currently in stable-queue which might be from [email protected] are

queue-3.18/ipv6-dccp-do-not-inherit-ipv6_mc_list-from-parent.patch queue-3.18/vlan-fix-a-use-after-free-in-vlan_device_event.patch