linux-kernel - Re: [PATCH] Add a sysctl option to disable bpf offensive helpers.

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Date:   Sat, 10 Jun 2023 08:37:28 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Yi He <clangllvm@....com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-trace-kernel@...r.kernel.org,
        Network Development <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>,
        LSM List <linux-security-module@...r.kernel.org>
Subject: Re: [PATCH] Add a sysctl option to disable bpf offensive helpers.

On Sat, Jun 10, 2023 at 4:21 AM Yi He <clangllvm@....com> wrote:
>
> Some eBPF helper functions have been long regarded as problematic[1].
> More than just used for powerful rootkit, these features can also be
> exploited to harm the containers by perform various attacks to the
> processes outside the container in the enrtire VM, such as process
> DoS, information theft, and container escape.
>
> When a container is granted to run eBPF tracing programs (which
> need CAP_SYS_ADMIN), it can use the eBPF KProbe programs to hijack the
> process outside the contianer and to escape the containers. This kind
> of risks is limited as privieleged containers are warned and can hardly
>  be accessed by the attackers.
>
> Even without CAP_SYS_ADMIN, since Linux 5.6, programs with with CAP_BPF +
> CAP_PERFMON can use dangerous eBPF helpers such as bpf_read_user to steal
> sensitive data (e.g., sshd/nginx private key) in other containers.

You can do the same completely without BPF and with just CAP_PERFMON.
I'm not going to share how, because you'll write a "security paper"
about insecure linux just like last time:
https://lore.kernel.org/bpf/20230117151256.605977-1-clangllvm@126.com/
Note, our answers didn't change. Look for security glory somewhere else.