linux-kernel - Re: [PATCH v0.9.1 3/6] sched/umcg: implement UMCG syscalls

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Message-ID: <20211124221833.GJ721624@worktop.programming.kicks-ass.net>
Date:   Wed, 24 Nov 2021 23:18:33 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Peter Oskolkov <posk@...k.io>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        Paul Turner <pjt@...gle.com>, Ben Segall <bsegall@...gle.com>,
        Peter Oskolkov <posk@...gle.com>,
        Andrei Vagin <avagin@...gle.com>, Jann Horn <jannh@...gle.com>,
        Thierry Delisle <tdelisle@...terloo.ca>
Subject: Re: [PATCH v0.9.1 3/6] sched/umcg: implement UMCG syscalls

On Mon, Nov 22, 2021 at 01:13:24PM -0800, Peter Oskolkov wrote:
> +die:
> +	pr_warn("%s: killing task %d\n", __func__, current->pid);
> +	force_sig(SIGKILL);

That pr_warn() might need to be pr_warn_ratelimited() in order to no be
a system log DoS.

Because, AFAICT, you can craft userspace to trigger this arbitrarily
often, just spawn a worker and make it misbehave.