linux-kernel - Re: [PATCH memcg] memcg: prohibit unconditional exceeding the limit of dying tasks

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: <4a407474-ff7a-9e4f-d314-ab85f0eeaadf@virtuozzo.com>
Date:   Fri, 10 Sep 2021 16:20:58 +0300
From:   Vasily Averin <vvs@...tuozzo.com>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     cgroups@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Michal Hocko <mhocko@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH memcg] memcg: prohibit unconditional exceeding the limit
 of dying tasks

On 9/10/21 4:04 PM, Tetsuo Handa wrote:
> On 2021/09/10 21:39, Vasily Averin wrote:
>> The kernel currently allows dying tasks to exceed the memcg limits.
>> The allocation is expected to be the last one and the occupied memory
>> will be freed soon.
>> This is not always true because it can be part of the huge vmalloc
>> allocation. Allowed once, they will repeat over and over again.
>> Moreover lifetime of the allocated object can differ from
>> In addition the lifetime of the dying task.
> 
> Can't we add fatal_signal_pending(current) test to vmalloc() loop?

1) this has been done in the past but has been reverted later.
2) any vmalloc changes will affect non-memcg allocations too.
 If we're doing memcg-related checks it's better to do it in one place.
3) it is not vmalloc-only issue. Huge number of  kmalloc page allocations 
from N concurrent threads will lead to the same problem. 

>> Multiple such allocations running concurrently can not only overuse
>> the memcg limit, but can lead to a global out of memory and,
>> in the worst case, cause the host to panic.
>>
>> Signed-off-by: Vasily Averin <vvs@...tuozzo.com>