Re: [oss-drivers] [PATCH AUTOSEL 5.4 326/350] bpf: Switch bpf_map ref counter to atomic64_t so bpf_map_inc() never fails

[Sasha Levin]

On Thu, Dec 12, 2019 at 05:25:13PM +0100, Daniel Borkmann wrote:
> On Tue, Dec 10, 2019 at 01:28:34PM -0800, Jakub Kicinski wrote:
> > On Tue, 10 Dec 2019 16:07:11 -0500, Sasha Levin wrote:
> > > From: Andrii Nakryiko <andriin@xxxxxx>
> > >
> > > [ Upstream commit 1e0bd5a091e5d9e0f1d5b0e6329b87bb1792f784 ]
> > >
> > > 92117d8443bc ("bpf: fix refcnt overflow") turned refcounting of bpf_map into
> > > potentially failing operation, when refcount reaches BPF_MAX_REFCNT limit
> > > (32k). Due to using 32-bit counter, it's possible in practice to overflow
> > > refcounter and make it wrap around to 0, causing erroneous map free, while
> > > there are still references to it, causing use-after-free problems.
> >
> > I don't think this is a bug fix, the second sentence here is written
> > in a quite confusing way, but there is no bug.
> >
> > Could you drop? I don't think it's worth the backporting pain since it
> > changes bpf_map_inc().
>
> Agree, this is not a bug fix and should not go to stable. (Also agree that
> the changelog is super confusing here and should have been done differently
> to avoid exactly where we are here. I think I pointed that out in the
> original patch, but seems this slipped through the cracks :/)

Sure, dropped, thanks!

--
Thanks,
Sasha