[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20110706185932.GB3299@albatros>
Date: Wed, 6 Jul 2011 22:59:32 +0400
From: Vasiliy Kulikov <segoon@...nwall.com>
To: kernel-hardening@...ts.openwall.com
Cc: linux-kernel@...r.kernel.org, Greg Kroah-Hartman <gregkh@...e.de>,
Andrew Morton <akpm@...ux-foundation.org>,
"David S. Miller" <davem@...emloft.net>,
Jiri Slaby <jslaby@...e.cz>, James Morris <jmorris@...ei.org>,
Neil Brown <neilb@...e.de>
Subject: Re: Re: RLIMIT_NPROC check in set_user()
On Wed, Jul 06, 2011 at 11:01 -0700, Linus Torvalds wrote:
> My reaction is: "let's just remote the crazy check from set_user()
> entirely".
Honestly, I didn't expect such a positive reaction from you in the first
reply :)
> The whole point of RLIMIT_NPROC is to avoid fork-bombs.
It is also used in cases where there is implicit or explicit limit on
some other resource per process leading to the global limit of
RLIMIT_NPROC*X. The most obvious case of X is RLIMIT_AS.
Purely pragmatic approach is introducing the check in execve() to
heuristically limit the number of user processes. If the program uses
PAM to register a user session, maxlogins from pam_limits is the Right
Way. But many programs simply don't use PAM because of the performance
issues. E.g. apache doesn't use PAM. On a shared web hosting this is a
real issue.
In -ow patch execve() checked for the exceeded RLIMIT_NPROC, which
effectively solved Apache's problem.
...and execve() error handling is hard to miss ;-)
> So let's keep it in kernel/fork.c where we actually create a *new*
> process (and where everybody knows exactly what the limit means, and
> people who don't check for error cases are just broken). And remove it
> from everywhere else.
There are checks only in copy_process() and set_user().
Thanks,
--
Vasiliy Kulikov
http://www.openwall.com - bringing security into open computing environments
Powered by blists - more mailing lists
Confused about mailing lists and their use?
Read about mailing lists on Wikipedia
and check out these
guidelines on proper formatting of your messages.
