netdev - Re: [PATCHv2 bpf-next 08/11] selftests/bpf: Add tests for reference tracking

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Date:   Wed, 26 Sep 2018 15:31:51 -0700
From:   Joe Stringer <joe@...d.net.nz>
To:     daniel@...earbox.net
Cc:     Joe Stringer <joe@...d.net.nz>, ast@...nel.org,
        netdev <netdev@...r.kernel.org>,
        john fastabend <john.fastabend@...il.com>, tgraf@...g.ch,
        Martin KaFai Lau <kafai@...com>,
        Nitin Hande <nitin.hande@...il.com>, mauricio.vasquez@...ito.it
Subject: Re: [PATCHv2 bpf-next 08/11] selftests/bpf: Add tests for reference tracking

On Mon, 24 Sep 2018 at 05:22, Daniel Borkmann <daniel@...earbox.net> wrote:
>
> On 09/21/2018 07:10 PM, Joe Stringer wrote:
> > reference tracking: leak potential reference
> > reference tracking: leak potential reference on stack
> > reference tracking: leak potential reference on stack 2
> > reference tracking: zero potential reference
> > reference tracking: copy and zero potential references
> > reference tracking: release reference without check
> > reference tracking: release reference
> > reference tracking: release reference twice
> > reference tracking: release reference twice inside branch
> > reference tracking: alloc, check, free in one subbranch
> > reference tracking: alloc, check, free in both subbranches
> > reference tracking in call: free reference in subprog
> > reference tracking in call: free reference in subprog and outside
> > reference tracking in call: alloc & leak reference in subprog
> > reference tracking in call: alloc in subprog, release outside
> > reference tracking in call: sk_ptr leak into caller stack
> > reference tracking in call: sk_ptr spill into caller stack
> >
> > Signed-off-by: Joe Stringer <joe@...d.net.nz>
> > Acked-by: Alexei Starovoitov <ast@...nel.org>
> > ---
> >  tools/testing/selftests/bpf/test_verifier.c | 359 ++++++++++++++++++++
> >  1 file changed, 359 insertions(+)
>
> I think this here needs to have some more test cases that we current do not track but
> should in order to have better coverage. At minimum what comes to mind additionally:
>
> - verifier interaction with LD_ABS, LD_IND
> - verifier interaction with tail calls (e.g. try to leak socket, socket_or_null, etc,
>   but should also have a positive test where we drop ref before tail call to show it
>   works in combination)
> - Try to mangle a socket and socket_or_null pointer with ALU ops and pass it to helper
> - Try to access the socket data fields after we released its reference
> - Access socket member fields in general (I think not present right now)
> - Use direct packet access in combination with lookup helper (it's enabled
>   via pkt_access = true in the helper, so we should also test for it here to make
>   sure future changes don't break it)

Great suggestions, I think that the LD_ABS/LD_IND ones are good
candidates for the assembly-level tests here. For the remainder, I
plan to add them to the C cases. That'll be easier to review and
easier to understand if they ever get broken.

Regarding the direct packet access with lookup, that's already in this
series in the C verifier tests patch.