linux-kernel - Re: kernel panic: Attempted to kill init!

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Date:   Thu, 5 Jan 2023 19:01:23 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Hao Sun <sunhao.th@...il.com>
Cc:     Yonghong Song <yhs@...a.com>, bpf <bpf@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        John Fastabend <john.fastabend@...il.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        David Miller <davem@...emloft.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: kernel panic: Attempted to kill init!

On Thu, Jan 5, 2023 at 1:00 AM Hao Sun <sunhao.th@...il.com> wrote:
> >
> > Does syzbot running without any user space?
> > Is syzbot itself a pid=1 ? and the only process ?
> > If so, the error would makes sense.
>
> Yes, after read the C reproducer again, noticed that after a
> bunch of sandbox setup, the pid of the reproducer process at
> runtime is 1.
>
> > I guess we can add a safety check to bpf_send_signal_common
> > to prevent syzbot from killing itself.
>
> Maybe something like this? This can avoid the panic, but won’t
> allow task with pid=1 to send signal with prog.
>
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 23ce498bca97..94d2af2ce433 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -844,6 +844,8 @@ static int bpf_send_signal_common(u32 sig, enum pid_type type)
>          */
>         if (unlikely(current->flags & (PF_KTHREAD | PF_EXITING)))
>                 return -EPERM;
> +       if (unlikely(is_global_init(current)))
> +               return -EPERM;
>         if (unlikely(!nmi_uaccess_okay()))
>                 return -EPERM;

Yep. Good idea. Pls send an official patch.