From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5E493C742A2 for ; Sun, 14 Jul 2019 07:14:05 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id E468120820 for ; Sun, 14 Jul 2019 07:14:04 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E468120820 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=cyphar.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 45mdF70G0NzDqWZ for ; Sun, 14 Jul 2019 17:14:03 +1000 (AEST) Authentication-Results: lists.ozlabs.org; spf=pass (mailfrom) smtp.mailfrom=cyphar.com (client-ip=80.241.60.212; helo=mx1.mailbox.org; envelope-from=cyphar@cyphar.com; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=cyphar.com Received: from mx1.mailbox.org (mx1.mailbox.org [80.241.60.212]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 45mdBW714dzDqRw for ; Sun, 14 Jul 2019 17:11:47 +1000 (AEST) Received: from smtp1.mailbox.org (smtp1.mailbox.org [IPv6:2001:67c:2050:105:465:1:1:0]) (using TLSv1.2 with cipher ECDHE-RSA-CHACHA20-POLY1305 (256/256 bits)) (No client certificate requested) by mx1.mailbox.org (Postfix) with ESMTPS id E49974EC6D; Sun, 14 Jul 2019 09:11:42 +0200 (CEST) X-Virus-Scanned: amavisd-new at heinlein-support.de Received: from smtp1.mailbox.org ([80.241.60.240]) by spamfilter02.heinlein-hosting.de (spamfilter02.heinlein-hosting.de [80.241.56.116]) (amavisd-new, port 10030) with ESMTP id so9n73IONPC7; Sun, 14 Jul 2019 09:11:17 +0200 (CEST) Date: Sun, 14 Jul 2019 17:11:02 +1000 From: Aleksa Sarai To: Al Viro Subject: Re: [PATCH v9 01/10] namei: obey trailing magic-link DAC permissions Message-ID: <20190714071102.gsc3kqpakz7chqt6@yavin> References: <20190706145737.5299-1-cyphar@cyphar.com> <20190706145737.5299-2-cyphar@cyphar.com> <20190712041454.GG17978@ZenIV.linux.org.uk> <20190712122017.xkowq2cjreylpotm@yavin> <20190712131005.GM17978@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="gghwwblfl4frle37" Content-Disposition: inline In-Reply-To: <20190712131005.GM17978@ZenIV.linux.org.uk> X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-ia64@vger.kernel.org, linux-sh@vger.kernel.org, Alexei Starovoitov , linux-kernel@vger.kernel.org, David Howells , linux-kselftest@vger.kernel.org, sparclinux@vger.kernel.org, Shuah Khan , linux-arch@vger.kernel.org, linux-s390@vger.kernel.org, Tycho Andersen , Aleksa Sarai , linux-arm-kernel@lists.infradead.org, linux-mips@vger.kernel.org, linux-xtensa@linux-xtensa.org, Kees Cook , Arnd Bergmann , Jann Horn , linuxppc-dev@lists.ozlabs.org, linux-m68k@lists.linux-m68k.org, Andy Lutomirski , Shuah Khan , David Drysdale , Christian Brauner , "J. Bruce Fields" , linux-parisc@vger.kernel.org, linux-api@vger.kernel.org, Chanho Min , Jeff Layton , Oleg Nesterov , Eric Biederman , linux-alpha@vger.kernel.org, linux-fsdevel@vger.kernel.org, Andrew Morton , Linus Torvalds , containers@lists.linux-foundation.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" --gghwwblfl4frle37 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On 2019-07-12, Al Viro wrote: > On Fri, Jul 12, 2019 at 10:20:17PM +1000, Aleksa Sarai wrote: > > On 2019-07-12, Al Viro wrote: > > > On Sun, Jul 07, 2019 at 12:57:28AM +1000, Aleksa Sarai wrote: > > > > @@ -514,7 +516,14 @@ static void set_nameidata(struct nameidata *p,= int dfd, struct filename *name) > > > > p->stack =3D p->internal; > > > > p->dfd =3D dfd; > > > > p->name =3D name; > > > > - p->total_link_count =3D old ? old->total_link_count : 0; > > > > + p->total_link_count =3D 0; > > > > + p->acc_mode =3D 0; > > > > + p->opath_mask =3D FMODE_PATH_READ | FMODE_PATH_WRITE; > > > > + if (old) { > > > > + p->total_link_count =3D old->total_link_count; > > > > + p->acc_mode =3D old->acc_mode; > > > > + p->opath_mask =3D old->opath_mask; > > > > + } > > >=20 > > > Huh? Could somebody explain why traversals of NFS4 referrals should = inherit > > > ->acc_mode and ->opath_mask? > >=20 > > I'll be honest -- I don't understand what set_nameidata() did so I just > > did what I thought would be an obvious change (to just copy the > > contents). I thought it was related to some aspect of the symlink stack > > handling. >=20 > No. It's handling of (very rare) nested pathwalk. The only case I can t= hink > of is handling of NFS4 referrals - they are triggered by ->d_automount() > and include NFS4 mount. Which does internal pathwalk of its own, to get > to the root of subtree being automounted. >=20 > NFS has its own recursion protection on that path (no deeper nesting than > one level of referral traversals), but there some nesting is inevitable; > we do get another nameidata instance on stack. And for nd_jump_link() we > need to keep track of the innermost one. >=20 > For symlinks nothing of that sort happens - they are dealt with on the sa= me > struct nameidata. ->total_link_count copying is there for one reason onl= y - > we want the total amount of symlinks traversed during the pathwalk (inclu= ding > the referral processing, etc.) to count towards MAXSYMLINKS check. It co= uld've > been moved from nameidata to task_struct, but it's cheaper to handle it t= hat > way. >=20 > Again, nesting is *rare*. Thanks for the explanation, much appreciated. I will drop the old->... copying hunk. > > In that case, should they both be set to 0 on set_nameidata()? This will > > mean that fd re-opening (or magic-link opening) through a > > set_nameidata() would always fail. >=20 > Huh? set_nameidata() is done for *all* instances - it's pretty much the > constructor of that object (and restore_nameidata() - a destructor). > Everything goes through it. Sorry, I meant to drop the copy-from-old logic -- not set it to zero explicitly in set_nameidata(). > And again, I'm not sure we want these fields in nameidata - IMO they belo= ng > in open_flags. Things like e.g. stat() don't need them at all. Yup, I'll work up a version that does the consolidation you mentioned in your other mail. > Incidentally, O_PATH opening of symlinks combined with subsequent procfs > symlink traversals is worth testing - that's where the things get subtle > and that's where it's easy to get in trouble on modifications. I have some self-tests of a symlink-to-a-magic-link in the last patch of the series. Did you mean something even more chained like a symlink to a /proc/self/fd/$n of an O_NOFOLLOW|O_PATH of a symlink? --=20 Aleksa Sarai Senior Software Engineer (Containers) SUSE Linux GmbH --gghwwblfl4frle37 Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iHUEABYIAB0WIQSxZm6dtfE8gxLLfYqdlLljIbnQEgUCXSrVgAAKCRCdlLljIbnQ EupPAQDpi9m99/xBGy4or9AS/LoRkr4tSLDlWlOsdCn0tZ52WAEAqoZwgZWyT46F mjKoRQeNjgtDk5jRNWbrwkJAMPXy2AE= =GnH+ -----END PGP SIGNATURE----- --gghwwblfl4frle37--