From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 21592 invoked by alias); 8 Oct 2014 13:41:10 -0000 Mailing-List: contact cygwin-help@cygwin.com; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: cygwin-owner@cygwin.com Mail-Followup-To: cygwin@cygwin.com Received: (qmail 21581 invoked by uid 89); 8 Oct 2014 13:41:10 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-5.9 required=5.0 tests=AWL,BAYES_00 autolearn=ham version=3.3.2 X-HELO: calimero.vinschen.de Received: from aquarius.hirmke.de (HELO calimero.vinschen.de) (217.91.18.234) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Wed, 08 Oct 2014 13:41:08 +0000 Received: by calimero.vinschen.de (Postfix, from userid 500) id 3C82C8E0A26; Wed, 8 Oct 2014 15:41:06 +0200 (CEST) Date: Wed, 08 Oct 2014 13:41:00 -0000 From: Corinna Vinschen To: cygwin@cygwin.com Subject: Re: Cannot exec() program outside of /bin if PATH is unset Message-ID: <20141008134106.GF29235@calimero.vinschen.de> Reply-To: cygwin@cygwin.com Mail-Followup-To: cygwin@cygwin.com References: <5413271B.1010109@t-online.de> <54134A83.80107@redhat.com> <54135451.3060902@t-online.de> <601154762.20140913012935@yandex.ru> <541378C4.6030705@t-online.de> <54137BDE.6040907@redhat.com> <54137C7F.1040507@redhat.com> <541415B1.8090500@t-online.de> <541698CC.7090802@lysator.liu.se> <5416F946.7010905@t-online.de> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="NGIwU0kFl1Z1A3An" Content-Disposition: inline In-Reply-To: <5416F946.7010905@t-online.de> User-Agent: Mutt/1.5.23 (2014-03-12) X-SW-Source: 2014-10/txt/msg00080.txt.bz2 --NGIwU0kFl1Z1A3An Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Content-length: 3363 On Sep 15 16:35, Christian Franke wrote: > Peter Rosin wrote: > >On 2014-09-13 12:00, Christian Franke wrote: > >>Note that setting PATH=3D/bin on Cygwin does not fix the security probl= em in the DLL search order. Even with "SafeDllSearchMode" enabled, the curr= ent directory is always checked before PATH. Running some Cygwin program fr= om /usr/sbin, /usr/local/bin, /usr/libexec, ... would load a possible malic= ious cyg*.dll from current directory regardless of PATH setting. Only progr= ams in /bin are safe. > >> > >>Using SetDllDirectory("c:\\cygwin\\bin") somewhere in cygwin1.dll would= fix this also. > >How could a call inside a DLL fix the library search order used > >to find that same DLL? Yes, it is possible (or likely) that > >SetDllDirectory fixes the immediate problem for processes that > >are started *by* cygwin1.dll, but it is not effective for Cygwin > >processes that are started by some direct use of the Win32 API. >=20 > Of course, and the same is true for any non-Cygwin program. The security = fix > is effective only for any CreateProcess()/LoadLibrary() call within the > process which called SetDllDirectory(DIR_OF_SUBSYSTEM_DLLs). >=20 >=20 > >Also, SetDllDirectory will kill all attempts to run 32-bit > >Cygwin programs from 64-bit Cygwin (and vice versa). >=20 > For programs in /bin directory, there is no problem because the EXE's > directory is always searched first for required DLLs. SetDllDirectory() t= hen > has no effect for cyg*.dll search order. >=20 > For other programs it also works because Windows (at least 7) apparently > skips 32-bit DLLs when searching for 64-bit ones (and vice versa). It is > then required that PATH contains the other Cygwin's /bin directory. >=20 > Testcase for calling 64-bit from 32-bit: >=20 > exe in /bin: >=20 > SetDllDirectory("c:\\cygwin\\bin"); > unsetenv("PATH"); > execl("/cygdrive/c/cygwin64/bin/uname", "uname", "-a", (const char*)0); >=20 > exe not in /bin: >=20 > SetDllDirectory("c:\\cygwin\\bin"); > setenv("PATH", "/cygdrive/c/cygwin64/bin", 1); > execl("/cygdrive/c/cygwin64/usr/sbin/alternatives", "alternatives", (co= nst > char*)0); >=20 > In both cases, the SetDllDirectory() call does not break anything. I'm somewhat reluctant to add a call to SetDllDirectory to the Cygwin DLL for two reasons. - Calling SetDllDirectory with an explicit dir doesn't just add this dir to the search path, it also removes the CWD from the search path. While I agree that this is a good thing from a security POV, can we be sure that this behaviour isn't needed somewhere, by somebody? - The fact that SetDllDirectory affects searching linked DLLs in calls to CreateProcess is undocumented. Per the original MSDN pages, SetDllDirectory affects calls to LoadLibrary and LoadLibraryEx, but not linked DLLs when starting a child process. The latter is only mentioned in a Community Addition: http://msdn.microsoft.com/en-us/library/windows/desktop/ms686203%28v=3Dvs= .85%29.aspx Having said that, we can certainly test this, but I'm wondering if an upstream Cygwin patch might be ok. Something similar has been applied to the portable OpenSSH repository years ago, so there's precedent. Corinna --=20 Corinna Vinschen Please, send mails regarding Cygwin to Cygwin Maintainer cygwin AT cygwin DOT com Red Hat --NGIwU0kFl1Z1A3An Content-Type: application/pgp-signature Content-length: 819 -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iQIcBAEBAgAGBQJUNT7yAAoJEPU2Bp2uRE+gzDkP/iOGNWZvsInG1AZOv7iKHk1V 7bnVpmuBNEChIWOv7m+fkvP3YM+o+6HiHiS0rBZXc8AuxF65/BVwTTTKVp47azYe c3rP1mwdYkv+hW/RaEdOrOPxJxpwIfasGyzx457Z5oToOR2gZNcuuRnXaTYoDvDt KONldjTpbMqfEyE5vlBKSiHbRN0ysRKADi6rETgkhd0DtjCXjKnV40RoPmY3ZrmH 1FmUujoPlBFo2ocnEGRGLkmWRWEWjmxOjBSJ3+CRwGlPS4iTSNBkp/d9OR1rYndf pby7XcBq0UsuQ0sfDQwOJze9Mw66K63fs9f3uTlGov+fObuTY6XxlhY/pNCyVe3I yQUuLsHyTZsNcfo0pw6x57aVvJXP3YOBSXcJtc/OjXVPUVpgvulhlVTE/KbLTA8S mc8uKa8xGxV/l5dFARltzmRsjD8MOKkKMOkbpBnOJeQBPyG6/eAJ7aFXVUD2LbZL MzoUy6jF59u1B7L0s0F8qe/ZtdiEMevYOvK/g4eR66FCbJ9XHOf6gLIpi2Qn7V8a 8Lc8fCokhxYSK2hArDGY6K3cdkaWmehp9sfVKERdBzecKhdGuqi7DwUbs9uPKOSS lHBnLvFR2hKoaKLjOQyhkUjkysUi4O4pCLKjHJLHdeXormMD7gPPKlw6EE2FQnfK Zhz4c8ttQo20gu7iCgxo =AQhM -----END PGP SIGNATURE----- --NGIwU0kFl1Z1A3An--