netdev - Re: [PATCH bpf v2 1/2] bpf: link: refuse non-O_RDWR flags in BPF_OBJ

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Date:   Wed, 31 Mar 2021 15:04:13 +0100
From:   Lorenz Bauer <lmb@...udflare.com>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Cc:     kernel-team <kernel-team@...udflare.com>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf v2 1/2] bpf: link: refuse non-O_RDWR flags in BPF_OBJ_GET

On Fri, 26 Mar 2021 at 16:05, Lorenz Bauer <lmb@...udflare.com> wrote:
>
> Invoking BPF_OBJ_GET on a pinned bpf_link checks the path access
> permissions based on file_flags, but the returned fd ignores flags.
> This means that any user can acquire a "read-write" fd for a pinned
> link with mode 0664 by invoking BPF_OBJ_GET with BPF_F_RDONLY in
> file_flags. The fd can be used to invoke BPF_LINK_DETACH, etc.
>
> Fix this by refusing non-O_RDWR flags in BPF_OBJ_GET. This works
> because OBJ_GET by default returns a read write mapping and libbpf
> doesn't expose a way to override this behaviour for programs
> and links.

Hi Alexei and Daniel,

I think these two patches might have fallen through the cracks, could
you take a look? I'm not sure what the etiquette is around bumping a
set, so please let me know if you'd prefer me to send the patches with
acks included or something like that.

Best

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

www.cloudflare.com