linux-kernel - Re: [PATCH] bpf: Add CONFIG_BPF_HELPER

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Message-ID: <CACYkzJ75aNbH4w_GzYjrNPKis1x24KOu_33DniY_ig5s3ycobg@mail.gmail.com>
Date:   Mon, 16 Jan 2023 22:39:12 +0100
From:   KP Singh <kpsingh@...nel.org>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Roland <kernel.pwn@...look.com>, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>, bsegall@...gle.com,
        Mel Gorman <mgorman@...e.de>, bristot <bristot@...hat.com>,
        vschneid@...hat.com, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH] bpf: Add CONFIG_BPF_HELPER_STRICT

On Sun, Jan 15, 2023 at 10:32 PM Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
>
> On Fri, Jan 13, 2023 at 11:53 PM Roland <kernel.pwn@...look.com> wrote:
> >
> > In container environment, ebpf helpers could be used maliciously to
> >    leak information, DOS, even escape from containers.
> >    CONFIG_BPF_HELPER_STRICT is as a mitigation of it.
> >    Related Link: https://rolandorange.zone/report.html
>
> The link is arguing that a process with CAP_SYS_ADMIN permissions
> can read memory of user processes, leak kernel addresses, etc.
> And this is somehow an issue with bpf helpers?
> and your suggested "temporary mitigation" is to CONFIG_BPF=n ?
> While this patch is a "proper fix" ?
> Sorry, but please stay with your "temporary mitigation" forever.

100% agreeing with Alexei here, if you are running your containers
with CAP_SYS_ADMIN there are a lot of other things you need to worry
about than just BPF helpers. You need to revisit your threat model and
consider not using CAP_SYS_ADMIN and more fine grained policies using
Mandatory Access Control.