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

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Message-ID: <CAEf4BzaEa0xQLvJbQTf9dE8DtjeetvqkUA=SbQHdjLHy+N04WQ@mail.gmail.com>
Date:   Wed, 29 May 2019 10:10:55 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Song Liu <liu.song.a23@...il.com>
Cc:     Andrii Nakryiko <andriin@...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 Wed, May 29, 2019 at 10:01 AM Song Liu <liu.song.a23@...il.com> wrote:
>
> 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)

sure, why not.

>
> > +               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?

yep, good point, will update

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