netdev - Re: [Patch net] vlan: fix a use-after-free in vlan_device

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Date:   Sat, 11 Nov 2017 19:36:07 +0900 (KST)
From:   David Miller <davem@...emloft.net>
To:     xiyou.wangcong@...il.com
Cc:     netdev@...r.kernel.org, fengguang.wu@...el.com,
        alexander.duyck@...il.com, torvalds@...ux-foundation.org,
        girish.moodalbail@...cle.com
Subject: Re: [Patch net] vlan: fix a use-after-free in vlan_device_event()

From: Cong Wang <xiyou.wangcong@...il.com>
Date: Thu,  9 Nov 2017 16:43:13 -0800

> 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>

Applied and queued up for -stable, thanks Cong!