lkml.org 
[lkml]   [2022]   [Feb]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: How should rlimits, suid exec, and capabilities interact?
Hi Andy,

On Wed, Feb 23, 2022 at 11:44:51AM -0800, Andy Lutomirski wrote:
> On Wed, Feb 23, 2022 at 10:00 AM Eric W. Biederman
> <ebiederm@xmission.com> wrote:
> >
> >
> > [CC'd the security list because I really don't know who the right people
> > are to drag into this discussion]
> >
> > While looking at some issues that have cropped up with making it so
> > that RLIMIT_NPROC cannot be escaped by creating a user namespace I have
> > stumbled upon a very old issue of how rlimits and suid exec interact
> > poorly.
>
> Once upon a time, these resource limits were effectively the only way
> to control memory consumption and consumption of historically limited
> resources like processes. (The scheduler used to have serious issues
> with too many processes -- this is not so true any more. And without
> cgroups, too many processes could use too much CPU collectively.)
> This all worked pretty poorly. Now we have cgroups, fancy memory
> accounting, etc. So I'm wondering if NPROC is even useful anymore. I
> don't have a brilliant idea of how to deprecate it, but I think it
> wouldn't be entirely nuts to take it much less seriously and maybe
> even eventually get rid of it.
>
> I doubt there is much existing userspace that would break if a
> previously failing fork() started succeeding.

I strongly disagree. I've been using it for a long time as a security
measure. Setting NPROC to 0 after daemonizing remains a particularly
effective and portable method to mitigate the possible consequences of
an in-process intrusion. While I wouldn't care about approximate non-zero
values, for me it would be a significant security regression to drop the
inability to fork() when the limit is zero. Thus at least I do want to
keep that feature when NPROC is zero.

Willy

\
 
 \ /
  Last update: 2022-02-23 22:29    [W:0.204 / U:0.368 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site