netdev - Re: [PATCH net-next v2 1/2] libbpf: parse maps sections of varying size

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Message-ID: <CAEfhGixvCWzQ4EHWnhO_djuNPj5-r1PraMtu6Csf_GNp83PEyA@mail.gmail.com>
Date:   Wed, 4 Oct 2017 09:58:41 -0400
From:   Craig Gallek <kraigatgoog@...il.com>
To:     Jesper Dangaard Brouer <brouer@...hat.com>
Cc:     Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        "David S . Miller" <davem@...emloft.net>,
        Chonggang Li <chonggangli@...gle.com>,
        netdev <netdev@...r.kernel.org>,
        Eric Leblond <eric.leblond@...il.com>
Subject: Re: [PATCH net-next v2 1/2] libbpf: parse maps sections of varying size

On Tue, Oct 3, 2017 at 10:11 AM, Jesper Dangaard Brouer
<brouer@...hat.com> wrote:
> On Mon,  2 Oct 2017 12:41:28 -0400
> Craig Gallek <kraigatgoog@...il.com> wrote:
>
>> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
>> index 4f402dcdf372..28b300868ad7 100644
>> --- a/tools/lib/bpf/libbpf.c
>> +++ b/tools/lib/bpf/libbpf.c
>> @@ -580,7 +580,7 @@ bpf_object__init_kversion(struct bpf_object *obj,
>>  }
>>
>>  static int
>> -bpf_object__validate_maps(struct bpf_object *obj)
>> +bpf_object__validate_maps(struct bpf_object *obj, int map_def_sz)
>>  {
>>       int i;
>>
>> @@ -595,9 +595,11 @@ bpf_object__validate_maps(struct bpf_object *obj)
>>               const struct bpf_map *a = &obj->maps[i - 1];
>>               const struct bpf_map *b = &obj->maps[i];
>>
>> -             if (b->offset - a->offset < sizeof(struct bpf_map_def)) {
>> -                     pr_warning("corrupted map section in %s: map \"%s\" too small\n",
>> -                                obj->path, a->name);
>> +             if (b->offset - a->offset < map_def_sz) {
>> +                     pr_warning("corrupted map section in %s: map \"%s\" too small "
>> +                                "(%zd vs %d)\n",
>> +                                obj->path, a->name, b->offset - a->offset,
>> +                                map_def_sz);
>>                       return -EINVAL;
>
> Hmm... one more comment.  You have just coded handling of ELF
> map_def_sz which are smaller in a safe manor, but here this case will
> get rejected (in bpf_object__validate_maps).  That cannot be the right
> intend?

I think you are right, but my test program didn't catch this...
Perhaps an off-by-one (I only used slightly smaller map_def sizes).  I
suppose this entire function is unnecessary now.  Even the old version
wouldn't catch the case where the last offset was out of bounds?

> --
> Best regards,
>   Jesper Dangaard Brouer
>   MSc.CS, Principal Kernel Engineer at Red Hat
>   LinkedIn: http://www.linkedin.com/in/brouer