netdev - Re: Use after free in __dst_destroy_metrics

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Date:   Fri, 08 Sep 2017 10:19:36 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     eric.dumazet@...il.com
Cc:     xiyou.wangcong@...il.com, subashab@...eaurora.org,
        netdev@...r.kernel.org, lorenzo@...gle.com
Subject: Re: Use after free in __dst_destroy_metrics_generic

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Fri, 08 Sep 2017 10:16:53 -0700

> On Fri, 2017-09-08 at 09:10 -0700, Cong Wang wrote:
>> On Thu, Sep 7, 2017 at 5:52 PM, Subash Abhinov Kasiviswanathan
>> <subashab@...eaurora.org> wrote:
>> > We are seeing a possible use after free in ip6_dst_destroy.
>> >
>> > It appears as if memory of the __DST_METRICS_PTR(old) was freed in some path
>> > and allocated
>> > to ion driver. ion driver has also freed it. Finally the memory is freed by
>> > the
>> > fib gc and crashes since it is already deallocated.
>> 
>> Does the attach (compile-only) patch help anything?
>> 
>> From my _quick_ glance, it seems we miss the refcnt'ing
>> right in __dst_destroy_metrics_generic().
>> 
>> Thanks!
> 
> But 4.9 kernels do not have yet the DST_METRICS_REFCOUNTED thing,
> since this was added in 4.12

It was backported via -stable.