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From: Florian Weimer <fweimer@redhat.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Carlos O'Donell <carlos@redhat.com>,
	Shawn Landden <shawn@git.icu>,
	libc-alpha@sourceware.org, linux-api@vger.kernel.org,
	LKML <linux-kernel@vger.kernel.org>,
	Arnd Bergmann <arnd@arndb.de>,
	Deepa Dinamani <deepa.kernel@gmail.com>,
	Oleg Nesterov <oleg@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Keith Packard <keithp@keithp.com>,
	Peter Zijlstra <peterz@infradead.org>
Subject: Re: [RFC v2 PATCH] futex: extend set_robust_list to allow 2 locking ABIs at the same time.
Date: Tue, 05 Nov 2019 15:33:38 +0100	[thread overview]
Message-ID: <87k18eqtod.fsf@oldenburg2.str.redhat.com> (raw)
In-Reply-To: <alpine.DEB.2.21.1911051520090.17054@nanos.tec.linutronix.de> (Thomas Gleixner's message of "Tue, 5 Nov 2019 15:27:54 +0100 (CET)")

* Thomas Gleixner:

> On Tue, 5 Nov 2019, Carlos O'Donell wrote:
>> On 11/5/19 6:56 AM, Thomas Gleixner wrote:
>> The other issue is this:
>> 
>> "Robust mutexes do not take ROBUST_LIST_LIMIT into account"
>> https://sourceware.org/bugzilla/show_bug.cgi?id=19089
>
>   "The kernel limits the length of the robust mutex list to 2048 entries.
>    This constant does not seem to be exported to user space."
>
> FWIW, the constant is defined in the UAPI futex header.
>
> The main concern here is not the actual number of futexes held by a task.
>
> The real issue is that the robust list could be circular by incident or
> malice and there is no way for the kernel to figure that out. That would
> prevent the task from exiting and make it iterate over the list until
> doomsday, i.e. a nice unpriviledged DoS.
>
> So I fear the kernel cannot really help with this one.

I'm actually fine with treating ROBUST_LIST_LIMIT as an ABI constant.
It's just not clear to me if the constant has this status today.  I
suspect it was just split from the implementation headers at one point.

Thanks,
Florian


  reply	other threads:[~2019-11-05 14:33 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-04  0:29 [RFC v2 PATCH] futex: extend set_robust_list to allow 2 locking ABIs at the same time Shawn Landden
2019-11-04  0:51 ` Shawn Landden
2019-11-04 15:37 ` Thomas Gleixner
2019-11-05  0:10   ` Thomas Gleixner
2019-11-05  9:48 ` Florian Weimer
2019-11-05  9:59   ` Thomas Gleixner
2019-11-05 10:06     ` Florian Weimer
2019-11-05 11:56       ` Thomas Gleixner
2019-11-05 14:10         ` Carlos O'Donell
2019-11-05 14:27           ` Florian Weimer
2019-11-05 14:53             ` Thomas Gleixner
2019-11-05 14:27           ` Thomas Gleixner
2019-11-05 14:33             ` Florian Weimer [this message]
2019-11-05 14:48               ` Thomas Gleixner
2019-11-06 14:00             ` Zack Weinberg
2019-11-06 14:04               ` Florian Weimer
2019-11-05 15:27     ` handle_exit_race && PF_EXITING Oleg Nesterov
2019-11-05 17:28       ` Thomas Gleixner
2019-11-05 17:59         ` Thomas Gleixner
2019-11-05 18:56           ` Thomas Gleixner
2019-11-05 19:19             ` Thomas Gleixner
2019-11-06  8:55               ` Oleg Nesterov
2019-11-06  9:53                 ` Thomas Gleixner
2019-11-06 10:35                   ` Oleg Nesterov
2019-11-06 11:07                     ` Thomas Gleixner
2019-11-06 12:11                       ` Oleg Nesterov
2019-11-06 13:38                         ` Thomas Gleixner
2019-11-06 17:42                         ` Thomas Gleixner
2019-11-07 15:51                           ` Oleg Nesterov

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