netdev - Re: Use after free in __dst_destroy_metrics

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Message-ID: <1504891013.15310.76.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Fri, 08 Sep 2017 10:16:53 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     Subash Abhinov Kasiviswanathan <subashab@...eaurora.org>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Lorenzo Colitti <lorenzo@...gle.com>
Subject: Re: Use after free in __dst_destroy_metrics_generic

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