netdev - Re: [PATCH 2/2] [net-next] bpf: fix out-of-bounds access warning in bpf

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Date:   Thu, 2 Nov 2017 17:14:00 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "David S. Miller" <davem@...emloft.net>,
        Edward Cree <ecree@...arflare.com>,
        John Fastabend <john.fastabend@...il.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Networking <netdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] [net-next] bpf: fix out-of-bounds access warning in bpf_check

On Thu, Nov 2, 2017 at 4:59 PM, Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
> On Thu, Nov 02, 2017 at 12:05:52PM +0100, Arnd Bergmann wrote:
>> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
>> index 750aff880ecb..debb60ad08ee 100644
>> --- a/kernel/bpf/verifier.c
>> +++ b/kernel/bpf/verifier.c
>> @@ -4447,6 +4447,10 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr)
>>       struct bpf_verifer_log *log;
>>       int ret = -EINVAL;
>>
>> +     /* no program is valid */
>> +     if (ARRAY_SIZE(bpf_verifier_ops) == 0)
>> +             return -EINVAL;
>
> sorry I don't see how bpf_verifier_ops can be empty.
> Did you mix it up with your previous patch when you made bpf_analyzer_ops empty?

I confused the two a couple of times while creating the patches, but
I'm still fairly
sure I got it right in the end:

bpf_verifier_ops is an array that gets generated by including linux/bpf_types.h.
That file has two kinds of entries:

- BPF_MAP_TYPE() entries are left out, as that macro is defined to an
empty string
  here.

- BPF_PROG_TYPE() entries are conditional depending on CONFIG_NET and
  CONFIG_BPF_EVENTS. In the configuration that produces the warning,
  both are disabled.

       Arnd