Re: [RFC v2 PATCH] futex: extend set_robust_list to allow 2 locking ABIs at the same time.
From: Florian Weimer
Date: Wed Nov 06 2019 - 09:04:44 EST
* Zack Weinberg:
> On Tue, Nov 5, 2019 at 9:28 AM Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
>>
>> 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.
>
> Why can't the kernel use the standard tortoise-and-hare algorithm for
> detecting circular linked lists here?
It's not guaranteed to terminate if the list is in shared memory.
Thanks,
Florian