linux-kernel - Re: general protection fault in put

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <ef0fe093-6fae-6c54-024b-fdec9c056af3@colorfullife.com>
Date:   Mon, 7 Jan 2019 19:04:55 +0100
From:   Manfred Spraul <manfred@...orfullife.com>
To:     Shakeel Butt <shakeelb@...gle.com>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        syzbot+1145ec2e23165570c3ac@...kaller.appspotmail.com,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Howells <dhowells@...hat.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        ktsanaktsidis@...desk.com, LKML <linux-kernel@...r.kernel.org>,
        Michal Hocko <mhocko@...e.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Matthew Wilcox <willy@...radead.org>,
        Davidlohr Bueso <dave@...olabs.net>
Subject: Re: general protection fault in put_pid

On 1/3/19 11:18 PM, Shakeel Butt wrote:
> Hi Manfred,
>
> On Sun, Dec 23, 2018 at 4:26 AM Manfred Spraul <manfred@...orfullife.com> wrote:
>> Hello Dmitry,
>>
>> On 12/23/18 10:57 AM, Dmitry Vyukov wrote:
>>> I can reproduce this infinite memory consumption with the C program:
>>> https://gist.githubusercontent.com/dvyukov/03ec54b3429ade16fa07bf8b2379aff3/raw/ae4f654e279810de2505e8fa41b73dc1d77778e6/gistfile1.txt
>>>
>>> But this is working as intended, right? It just creates infinite
>>> number of large semaphore sets, which reasonably consumes infinite
>>> amount of memory.
>>> Except that it also violates the memcg bound and a process can have
>>> effectively unlimited amount of such "drum memory" in semaphores.
>> Yes, this is as intended:
>>
>> If you call semget(), then you can use memory, up to the limits in
>> /proc/sys/kernel/sem.
>>
>> Memcg is not taken into account, an admin must set /proc/sys/kernel/sem.
>>
>> The default are "infinite amount of memory allowed", as this is the most
>> sane default: We had a logic that tried to autotune (i.e.: a new
>> namespace "inherits" a fraction of the parent namespaces memory limits),
>> but this we more or less always wrong.
>>
>>
> What's the disadvantage of setting the limits in /proc/sys/kernel/sem
> high and let the task's memcg limits the number of semaphore a process
> can create? Please note that the memory underlying shmget and msgget
> is already accounted to memcg.

Nothing, it it just a question of implementing it.

I'll try to look at it.

--

     Manfred