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

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Date:   Thu, 1 Apr 2021 11:04:31 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Lorenz Bauer <lmb@...udflare.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        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 Wed, Mar 31, 2021 at 7:04 AM Lorenz Bauer <lmb@...udflare.com> wrote:
>
> 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.

It is still in patchworks. I didn't have time to think it through.
Sorry for delay.