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

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Message-ID: <5488924B.5070502@redhat.com>
Date:	Wed, 10 Dec 2014 16:34:51 -0200
From:	Marcelo Ricardo Leitner <mleitner@...hat.com>
To:	David Miller <davem@...emloft.net>
CC:	netdev@...r.kernel.org
Subject: Re: [PATCH net] Fix race condition between vxlan_sock_add and vxlan_sock_release

On 10-12-2014 16:11, David Miller wrote:
> From: Marcelo Ricardo Leitner <mleitner@...hat.com>
> Date: Tue,  9 Dec 2014 12:28:28 -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
>
> Just make vxlan_sock_add() do atomic_add_unless(x, 1, 0), that way
> if vxlan_sock_add() sees the count at zero it can just act as if
> no such reusable socket exists.

Interesting, I had thought of this, but it seemed a bit messy.
But okay, I see the pros on it, will go that way. Thanks!

   Marcelo

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