netdev - Re: [PATCH bpf] bpf: fix OOB read when printing XDP link fdinfo

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Message-ID: <CACAyw98RaF8SgA9nkduXo-wBdsRN86cP=seX9d83i0Qhi0gbeQ@mail.gmail.com>
Date:   Mon, 19 Jul 2021 09:45:16 +0100
From:   Lorenz Bauer <lmb@...udflare.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        kernel-team <kernel-team@...udflare.com>,
        Andrii Nakryiko <andriin@...com>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf] bpf: fix OOB read when printing XDP link fdinfo

On Fri, 16 Jul 2021 at 21:44, Andrii Nakryiko <andrii.nakryiko@...il.com> wrote:
>
> Well, oops. Thanks for the fix!
>
> Acked-by: Andrii Nakryiko <andrii@...nel.org>
>
> It would be great to have a compilation error for something like this.
> I wonder if we can do something to detect this going forward?

I had a second patch that introduced MAX_BPF_LINK_TYPE, etc. and then
added explicit array initializers:

     [MAX_BPF_LINK_TYPE] = NULL,

That turns the OOB read into a NULL read. But it has to be done for
every inclusion of bpf_types.h so it's
a bit cumbersome. Maybe add MAX_BPF_LINK_TYPE and then add an entry in
bpf_types.h for it as well?

--
Lorenz Bauer  |  Systems Engineer
6th Floor, County Hall/The Riverside Building, SE1 7PB, UK

www.cloudflare.com