netdev - Re: Use after free in __dst_destroy_metrics

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Date:   Fri, 08 Sep 2017 10:28:57 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     David Miller <davem@...emloft.net>
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

On Fri, 2017-09-08 at 10:19 -0700, David Miller wrote:
> 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.

I hate working on lazy bug reports.