netdev - Re: [PATCH net v2] Fix race condition between vxlan_sock_add and vxlan_sock

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Date:	Thu, 11 Dec 2014 14:57:40 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	mleitner@...hat.com
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH net v2] Fix race condition between vxlan_sock_add and
 vxlan_sock_release

From: Marcelo Ricardo Leitner <mleitner@...hat.com>
Date: Thu, 11 Dec 2014 10:02:22 -0200

> Currently, when trying to reuse a socket, vxlan_sock_add will grab
> vn->sock_lock, locate a reusable socket, inc refcount and release
> vn->sock_lock.
> 
> But vxlan_sock_release() will first decrement refcount, and then grab
> that lock. refcnt operations are atomic but as currently we have
> deferred works which hold vs->refcnt each, this might happen, leading to
> a use after free (specially after vxlan_igmp_leave):
> 
>   CPU 1                            CPU 2
> 
> deferred work                    vxlan_sock_add
>   ...                              ...
>                                    spin_lock(&vn->sock_lock)
>                                    vs = vxlan_find_sock();
>   vxlan_sock_release
>     dec vs->refcnt, reaches 0
>     spin_lock(&vn->sock_lock)
>                                    vxlan_sock_hold(vs), refcnt=1
>                                    spin_unlock(&vn->sock_lock)
>     hlist_del_rcu(&vs->hlist);
>     vxlan_notify_del_rx_port(vs)
>     spin_unlock(&vn->sock_lock)
> 
> 
> So when we look for a reusable socket, we check if it wasn't freed
> already before reusing it.
> 
> Signed-off-by: Marcelo Ricardo Leitner <mleitner@...hat.com>
> Fixes: 7c47cedf43a8b3 ("vxlan: move IGMP join/leave to work queue")

Applied and queued up for -stable, thanks.
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