|From:||Vasiliy Kulikov <segoon-AT-openwall.com>|
|Subject:||Re: [kernel-hardening] Re: RLIMIT_NPROC check in set_user()|
|Date:||Wed, 6 Jul 2011 22:59:32 +0400|
|Cc:||linux-kernel-AT-vger.kernel.org, Greg Kroah-Hartman <gregkh-AT-suse.de>, Andrew Morton <akpm-AT-linux-foundation.org>, "David S. Miller" <davem-AT-davemloft.net>, Jiri Slaby <jslaby-AT-suse.cz>, James Morris <jmorris-AT-namei.org>, Neil Brown <neilb-AT-suse.de>|
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
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