Re: Use after free in __dst_destroy_metrics_generic

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

From: Eric Dumazet <redacted>
Date: Fri, 08 Sep 2017 10:16:53 -0700

quoted

On Fri, 2017-09-08 at 09:10 -0700, Cong Wang wrote:

quoted

On Thu, Sep 7, 2017 at 5:52 PM, Subash Abhinov Kasiviswanathan
[off-list ref] wrote:

quoted

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.