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

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Date:   Thu, 2 Nov 2017 10:58:46 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        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>,
        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, 2 Nov 2017 17:14:00 +0100, Arnd Bergmann wrote:
> On Thu, Nov 2, 2017 at 4:59 PM, Alexei Starovoitov 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.

Right.  My preferred fix was to add a NULL entry to the table so it's
never empty, but this is OK too.  Thanks!