linux-kernel - Re: [PATCH bpf-next v3 6/6] selftests/bpf: Add a series of tests for bpf

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAEf4BzZ6cLio0ZZEkc5iYp9yWg3Fc1ZORBTr85TdoqF-sRU3DQ@mail.gmail.com>
Date:   Tue, 13 Apr 2021 16:21:42 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Florent Revest <revest@...omium.org>
Cc:     bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Yonghong Song <yhs@...com>, KP Singh <kpsingh@...nel.org>,
        Brendan Jackman <jackmanb@...omium.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf-next v3 6/6] selftests/bpf: Add a series of tests for bpf_snprintf

On Mon, Apr 12, 2021 at 8:38 AM Florent Revest <revest@...omium.org> wrote:
>
> This exercises most of the format specifiers.
>
> Signed-off-by: Florent Revest <revest@...omium.org>
> Acked-by: Andrii Nakryiko <andrii@...nel.org>
> ---

As I mentioned on another patch, we probably need negative tests even
more than positive ones.

I think an easy and nice way to do this is to have a separate BPF
skeleton where fmt string and arguments are provided through read-only
global variables, so that user-space can re-use the same BPF skeleton
to simulate multiple cases. BPF program itself would just call
bpf_snprintf() and store the returned result.

Whether we need to validate the verifier log is up to debate (though
it's not that hard to do by overriding libbpf_print_fn() callback),
I'd be ok at least knowing that some bad format strings are rejected
and don't crash the kernel.

>  .../selftests/bpf/prog_tests/snprintf.c       | 81 +++++++++++++++++++
>  .../selftests/bpf/progs/test_snprintf.c       | 74 +++++++++++++++++
>  2 files changed, 155 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/snprintf.c
>  create mode 100644 tools/testing/selftests/bpf/progs/test_snprintf.c
>

[...]