Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:18 as permitted sender) client-ip=2620:137:e000::1:18;
Message-ID: <19b324a4-f69c-1624-fbc7-e178b7c31d81@redhat.com>
Date:   Fri, 22 Apr 2022 10:12:39 -0400
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.5.0
Subject: Re: [RFC 2/3] futex: exit: Print a warning when futex_cleanup fails
Content-Language: en-US
To:     Matthew Wilcox <willy@infradead.org>
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Darren Hart <dvhart@infradead.org>,
        Davidlohr Bueso <dave@stgolabs.net>,
        =?UTF-8?Q?Andr=c3=a9_Almeida?= <andrealmeid@collabora.com>,
        Arjan van de Ven <arjan@infradead.org>,
        Ulrich Drepper <drepper@redhat.com>
References: <20220421190533.1601879-1-npache@redhat.com>
 <20220421190533.1601879-3-npache@redhat.com>
 <YmGwzRIHFlKZk3Hm@casper.infradead.org>
From:   Nico Pache <npache@redhat.com>
In-Reply-To: <YmGwzRIHFlKZk3Hm@casper.infradead.org>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Precedence: bulk


On 4/21/22 15:30, Matthew Wilcox wrote:
> On Thu, Apr 21, 2022 at 03:05:32PM -0400, Nico Pache wrote:
>> @@ -1007,13 +1013,15 @@ static inline void exit_pi_state_list(struct task_struct *curr) { }
>>  static void futex_cleanup(struct task_struct *tsk)
>>  {
>>  	if (unlikely(tsk->robust_list)) {
>> -		exit_robust_list(tsk);
>> +		if (!exit_robust_list(tsk))
>> +			pr_info("futex: exit_robust_list failed");
> 
> Doesn't this allow a malicious user process to spam the kernel logs
> with messages?  There needs to be a ratelimit on this, at least.
Fair point, we'd need a ratelimited print if we want to continue forward with
this. Additionally we may want to limit this print to debug kernels, but thats
just a thought.

Thanks for the review :)
-- Nico