From mboxrd@z Thu Jan 1 00:00:00 1970 Reply-To: kernel-hardening@lists.openwall.com Sender: Vasiliy Kulikov Date: Wed, 6 Jul 2011 22:59:32 +0400 From: Vasiliy Kulikov Message-ID: <20110706185932.GB3299@albatros> References: <20110612130953.GA3709@albatros> <20110706173631.GA5431@albatros> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Subject: Re: [kernel-hardening] Re: RLIMIT_NPROC check in set_user() To: kernel-hardening@lists.openwall.com Cc: linux-kernel@vger.kernel.org, Greg Kroah-Hartman , Andrew Morton , "David S. Miller" , Jiri Slaby , James Morris , Neil Brown List-ID: 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