linux-hardening - Re: [PATCH v2 5/6] panic: Introduce warn

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Date:   Mon, 14 Nov 2022 10:48:38 +0100
From:   Marco Elver <elver@...gle.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Jann Horn <jannh@...gle.com>, Jonathan Corbet <corbet@....net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Eric Biggers <ebiggers@...gle.com>,
        Huang Ying <ying.huang@...el.com>,
        Petr Mladek <pmladek@...e.com>,
        tangmeng <tangmeng@...ontech.com>,
        "Guilherme G. Piccoli" <gpiccoli@...lia.com>,
        Tiezhu Yang <yangtiezhu@...ngson.cn>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        linux-doc@...r.kernel.org, Greg KH <gregkh@...uxfoundation.org>,
        Linus Torvalds <torvalds@...uxfoundation.org>,
        Seth Jenkins <sethjenkins@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Arnd Bergmann <arnd@...db.de>,
        Dmitry Vyukov <dvyukov@...gle.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>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Alexander Potapenko <glider@...gle.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Luis Chamberlain <mcgrof@...nel.org>,
        David Gow <davidgow@...gle.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Anton Vorontsov <anton@...msg.org>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        Laurent Dufour <ldufour@...ux.ibm.com>,
        Rob Herring <robh@...nel.org>, linux-kernel@...r.kernel.org,
        kasan-dev@...glegroups.com, linux-mm@...ck.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2 5/6] panic: Introduce warn_limit

On Wed, 9 Nov 2022 at 21:00, Kees Cook <keescook@...omium.org> wrote:
>
> Like oops_limit, add warn_limit for limiting the number of warnings when
> panic_on_warn is not set.
>
> Cc: Jonathan Corbet <corbet@....net>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Baolin Wang <baolin.wang@...ux.alibaba.com>
> Cc: "Jason A. Donenfeld" <Jason@...c4.com>
> Cc: Eric Biggers <ebiggers@...gle.com>
> Cc: Huang Ying <ying.huang@...el.com>
> Cc: Petr Mladek <pmladek@...e.com>
> Cc: tangmeng <tangmeng@...ontech.com>
> Cc: "Guilherme G. Piccoli" <gpiccoli@...lia.com>
> Cc: Tiezhu Yang <yangtiezhu@...ngson.cn>
> Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> Cc: linux-doc@...r.kernel.org
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
>  Documentation/admin-guide/sysctl/kernel.rst |  9 +++++++++
>  kernel/panic.c                              | 13 +++++++++++++
>  2 files changed, 22 insertions(+)
>
> diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
> index 09f3fb2f8585..c385d5319cdf 100644
> --- a/Documentation/admin-guide/sysctl/kernel.rst
> +++ b/Documentation/admin-guide/sysctl/kernel.rst
> @@ -1508,6 +1508,15 @@ entry will default to 2 instead of 0.
>  2 Unprivileged calls to ``bpf()`` are disabled
>  = =============================================================
>
> +
> +warn_limit
> +==========
> +
> +Number of kernel warnings after which the kernel should panic when
> +``panic_on_warn`` is not set. Setting this to 0 or 1 has the same effect
> +as setting ``panic_on_warn=1``.
> +
> +
>  watchdog
>  ========
>
> diff --git a/kernel/panic.c b/kernel/panic.c
> index 3afd234767bc..b235fa4a6fc8 100644
> --- a/kernel/panic.c
> +++ b/kernel/panic.c
> @@ -58,6 +58,7 @@ bool crash_kexec_post_notifiers;
>  int panic_on_warn __read_mostly;
>  unsigned long panic_on_taint;
>  bool panic_on_taint_nousertaint = false;
> +static unsigned int warn_limit __read_mostly = 10000;
>
>  int panic_timeout = CONFIG_PANIC_TIMEOUT;
>  EXPORT_SYMBOL_GPL(panic_timeout);
> @@ -88,6 +89,13 @@ static struct ctl_table kern_panic_table[] = {
>                 .extra2         = SYSCTL_ONE,
>         },
>  #endif
> +       {
> +               .procname       = "warn_limit",
> +               .data           = &warn_limit,
> +               .maxlen         = sizeof(warn_limit),
> +               .mode           = 0644,
> +               .proc_handler   = proc_douintvec,
> +       },
>         { }
>  };
>
> @@ -203,8 +211,13 @@ static void panic_print_sys_info(bool console_flush)
>
>  void check_panic_on_warn(const char *reason)
>  {
> +       static atomic_t warn_count = ATOMIC_INIT(0);
> +
>         if (panic_on_warn)
>                 panic("%s: panic_on_warn set ...\n", reason);
> +
> +       if (atomic_inc_return(&warn_count) >= READ_ONCE(warn_limit))
> +               panic("Warned too often (warn_limit is %d)", warn_limit);

Shouldn't this also include the "reason", like above? (Presumably a
warning had just been generated to console so the reason is easy
enough to infer from the log, although in that case "reason" also
seems redundant above.)