linux-kernel - Re: [PATCH] mm: disable `vm.max_map

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: <20171127183218.33zm666jw3uqkxdq@dhcp22.suse.cz>
Date:   Mon, 27 Nov 2017 19:32:18 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Andi Kleen <ak@...ux.intel.com>
Cc:     Mikael Pettersson <mikpelinux@...il.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-api@...r.kernel.org
Subject: Re: [PATCH] mm: disable `vm.max_map_count' sysctl limit

On Mon 27-11-17 09:25:16, Andi Kleen wrote:
> Michal Hocko <mhocko@...nel.org> writes:
> >
> > Could you be more explicit about _why_ we need to remove this tunable?
> > I am not saying I disagree, the removal simplifies the code but I do not
> > really see any justification here.
> 
> It's an arbitrary scaling limit on the how many mappings the process
> has. The more memory you have the bigger a problem it is. We've
> ran into this problem too on larger systems.

Why cannot you increase the limit?

> The reason the limit was there originally because it allows a DoS
> attack against the kernel by filling all unswappable memory up with VMAs.

We can reduce the effect by accounting vmas to memory cgroups.
-- 
Michal Hocko
SUSE Labs