netdev - Re: [PATCH bpf-next 1/9] libbpf: fix detection of corrupted BPF instructions section

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Message-ID: <CAPhsuW7zZ=QQs2wpR46+0hydSzRYza2_7kSAr0a1nBChSHbu6Q@mail.gmail.com>
Date:   Wed, 29 May 2019 10:01:20 -0700
From:   Song Liu <liu.song.a23@...il.com>
To:     Andrii Nakryiko <andriin@...com>
Cc:     Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH bpf-next 1/9] libbpf: fix detection of corrupted BPF
 instructions section

On Tue, May 28, 2019 at 6:14 PM Andrii Nakryiko <andriin@...com> wrote:
>
> Ensure that size of a section w/ BPF instruction is exactly a multiple
> of BPF instruction size.
>
> Signed-off-by: Andrii Nakryiko <andriin@...com>
> ---
>  tools/lib/bpf/libbpf.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index ca4432f5b067..05a73223e524 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -349,8 +349,11 @@ static int
>  bpf_program__init(void *data, size_t size, char *section_name, int idx,
>                   struct bpf_program *prog)
>  {
> -       if (size < sizeof(struct bpf_insn)) {
> -               pr_warning("corrupted section '%s'\n", section_name);
> +       const size_t bpf_insn_sz = sizeof(struct bpf_insn);
> +
> +       if (size < bpf_insn_sz || size % bpf_insn_sz) {

how about
           if (!size || size % bpf_insn_sz)

> +               pr_warning("corrupted section '%s', size: %zu\n",
> +                          section_name, size);
>                 return -EINVAL;
>         }
>
> @@ -376,9 +379,8 @@ bpf_program__init(void *data, size_t size, char *section_name, int idx,
>                            section_name);
>                 goto errout;
>         }
> -       prog->insns_cnt = size / sizeof(struct bpf_insn);
> -       memcpy(prog->insns, data,
> -              prog->insns_cnt * sizeof(struct bpf_insn));
> +       prog->insns_cnt = size / bpf_insn_sz;
> +       memcpy(prog->insns, data, prog->insns_cnt * bpf_insn_sz);

Given the check above, we can just use size in memcpy, right?

Thanks,
Song

>         prog->idx = idx;
>         prog->instances.fds = NULL;
>         prog->instances.nr = -1;
> --
> 2.17.1
>