linux-kernel - Re: [PATCH] move RLIMIT_NPROC check from set_user() to do_execve

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Date:	Wed, 13 Jul 2011 14:36:57 +0900
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	segoon@...nwall.com
CC:	torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
	gregkh@...e.de, akpm@...ux-foundation.org, davem@...emloft.net,
	kernel-hardening@...ts.openwall.com, jslaby@...e.cz,
	jmorris@...ei.org, neilb@...e.de, viro@...iv.linux.org.uk,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] move RLIMIT_NPROC check from set_user() to do_execve_common()

(2011/07/12 22:27), Vasiliy Kulikov wrote:
> The patch http://lkml.org/lkml/2003/7/13/226 introduced a RLIMIT_NPROC
> check in set_user() to check for NPROC exceeding via setuid() and
> similar functions.  Before the check there was a possibility to greatly
> exceed the allowed number of processes by an unprivileged user if the
> program relied on rlimit only.  But the check created new security
> threat: many poorly written programs simply don't check setuid() return
> code and believe it cannot fail if executed with root privileges.  So,
> the check is removed in this patch because of too often privilege
> escalations related to buggy programs.
> 
> The NPROC can still be enforced in the common code flow of daemons
> spawning user processes.  Most of daemons do fork()+setuid()+execve().
> The check introduced in execve() enforces the same limit as in setuid()
> and doesn't create similar security issues.
> 
> Similar check was introduced in -ow patches.
> 
> Signed-off-by: Vasiliy Kulikov <segoon@...nwall.com>

BSD folks tell me NetBSD has the exactly same hack (ie check at exec instead
setuid) since 2008. Then, I think this is enough proved safer way.

http://cvsweb.netbsd.org/bsdweb.cgi/src/sys/kern/kern_exec.c?rev=1.316&content-type=text/x-cvsweb-markup&only_with_tag=MAIN

Thx.



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