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=-0.7 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 9D24FCA9EBC for ; Thu, 24 Oct 2019 07:15:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7C76921A4A for ; Thu, 24 Oct 2019 07:15:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2437946AbfJXHPi (ORCPT ); Thu, 24 Oct 2019 03:15:38 -0400 Received: from mout-p-102.mailbox.org ([80.241.56.152]:11570 "EHLO mout-p-102.mailbox.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2437940AbfJXHPh (ORCPT ); Thu, 24 Oct 2019 03:15:37 -0400 Received: from smtp2.mailbox.org (smtp2.mailbox.org [IPv6:2001:67c:2050:105:465:1:2:0]) (using TLSv1.2 with cipher ECDHE-RSA-CHACHA20-POLY1305 (256/256 bits)) (No client certificate requested) by mout-p-102.mailbox.org (Postfix) with ESMTPS id 46zJFS55d2zKmhs; Thu, 24 Oct 2019 09:06:36 +0200 (CEST) X-Virus-Scanned: amavisd-new at heinlein-support.de Received: from smtp2.mailbox.org ([80.241.60.241]) by gerste.heinlein-support.de (gerste.heinlein-support.de [91.198.250.173]) (amavisd-new, port 10030) with ESMTP id DAIjq9oYK49d; Thu, 24 Oct 2019 09:06:30 +0200 (CEST) Date: Thu, 24 Oct 2019 18:06:04 +1100 From: Aleksa Sarai To: Linus Torvalds Cc: Al Viro , Jeff Layton , "J. Bruce Fields" , Arnd Bergmann , David Howells , Shuah Khan , Shuah Khan , Ingo Molnar , Peter Zijlstra , Eric Biederman , Andy Lutomirski , Andrew Morton , Alexei Starovoitov , Kees Cook , Jann Horn , Tycho Andersen , David Drysdale , Chanho Min , Oleg Nesterov , Rasmus Villemoes , Alexander Shishkin , Jiri Olsa , Namhyung Kim , Christian Brauner , Aleksa Sarai , Linux Containers , alpha , Linux API , GNU C Library , linux-arch , Linux ARM , linux-fsdevel , linux-ia64@vger.kernel.org, Linux Kernel Mailing List , "open list:KERNEL SELFTEST FRAMEWORK" , linux-m68k , linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390 , Linux-sh list , linux-xtensa@linux-xtensa.org, sparclinux@vger.kernel.org Subject: Re: [PATCH v14 2/6] namei: LOOKUP_IN_ROOT: chroot-like path resolution Message-ID: <20191024070604.howuh6x6qrzd5jsm@yavin.dot.cyphar.com> References: <20191010054140.8483-1-cyphar@cyphar.com> <20191010054140.8483-3-cyphar@cyphar.com> <20191012040815.gnc43cfmo5mnv67u@yavin.dot.cyphar.com> <20191012041541.milbmfbjpj5bcl5a@yavin.dot.cyphar.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="i56sxfhksaspu3tw" Content-Disposition: inline In-Reply-To: <20191012041541.milbmfbjpj5bcl5a@yavin.dot.cyphar.com> Sender: linux-parisc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-parisc@vger.kernel.org --i56sxfhksaspu3tw Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On 2019-10-12, Aleksa Sarai wrote: > On 2019-10-12, Aleksa Sarai wrote: > > On 2019-10-10, Linus Torvalds wrote: > > > On Wed, Oct 9, 2019 at 10:42 PM Aleksa Sarai wrot= e: > > > > > > > > --- a/fs/namei.c > > > > +++ b/fs/namei.c > > > > @@ -2277,6 +2277,11 @@ static const char *path_init(struct nameidat= a *nd, unsigned flags) > > > > > > > > nd->m_seq =3D read_seqbegin(&mount_lock); > > > > > > > > + /* LOOKUP_IN_ROOT treats absolute paths as being relative-t= o-dirfd. */ > > > > + if (flags & LOOKUP_IN_ROOT) > > > > + while (*s =3D=3D '/') > > > > + s++; > > > > + > > > > /* Figure out the starting path and root (if needed). */ > > > > if (*s =3D=3D '/') { > > > > error =3D nd_jump_root(nd); > > >=20 > > > Hmm. Wouldn't this make more sense all inside the if (*s =3D- '/') te= st? > > > That way if would be where we check for "should we start at the root", > > > which seems to make more sense conceptually. > >=20 > > I don't really agree (though I do think that both options are pretty > > ugly). Doing it before the block makes it clear that absolute paths are > > just treated relative-to-dirfd -- doing it inside the block makes it > > look more like "/" is a special-case for nd_jump_root(). And while that >=20 > Sorry, I meant "special-case for LOOKUP_IN_ROOT". >=20 > > is somewhat true, this is just a side-effect of making the code more > > clean -- my earlier versions reworked the dirfd handling to always grab > > nd->root first if LOOKUP_IS_SCOPED. I switched to this method based on > > Al's review. > >=20 > > In fairness, I do agree that the lonely while loop looks ugly. >=20 > And with the old way I did it (where we grabbed nd->root first) the > semantics were slightly more clear -- stripping leading "/"s doesn't > really look as "clearly obvious" as grabbing nd->root beforehand and > treating "/"s normally. But the code was also needlessly more complex. >=20 > > > That test for '/' currently has a "} else if (..)", but that's > > > pointless since it ends with a "return" anyway. So the "else" logic is > > > just noise. > >=20 > > This depends on the fact that LOOKUP_BENEATH always triggers -EXDEV for > > nd_jump_root() -- if we ever add another "scoped lookup" flag then the > > logic will have to be further reworked. > >=20 > > (It should be noted that the new version doesn't always end with a > > "return", but you could change it to act that way given the above > > assumption.) > >=20 > > > And if you get rid of the unnecessary else, moving the LOOKUP_IN_ROOT > > > inside the if-statement works fine. > > >=20 > > > So this could be something like > > >=20 > > > --- a/fs/namei.c > > > +++ b/fs/namei.c > > > @@ -2194,11 +2196,19 @@ static const char *path_init(struct > > > nameidata *nd, unsigned flags) > > >=20 > > > nd->m_seq =3D read_seqbegin(&mount_lock); > > > if (*s =3D=3D '/') { > > > - set_root(nd); > > > - if (likely(!nd_jump_root(nd))) > > > - return s; > > > - return ERR_PTR(-ECHILD); > > > - } else if (nd->dfd =3D=3D AT_FDCWD) { > > > + /* LOOKUP_IN_ROOT treats absolute paths as being > > > relative-to-dirfd. */ > > > + if (!(flags & LOOKUP_IN_ROOT)) { > > > + set_root(nd); > > > + if (likely(!nd_jump_root(nd))) > > > + return s; > > > + return ERR_PTR(-ECHILD); > > > + } > > > + > > > + /* Skip initial '/' for LOOKUP_IN_ROOT */ > > > + do { s++; } while (*s =3D=3D '/'); > > > + } > > > + > > > + if (nd->dfd =3D=3D AT_FDCWD) { > > > if (flags & LOOKUP_RCU) { > > > struct fs_struct *fs =3D current->fs; > > > unsigned seq; > > >=20 > > > instead. The patch ends up slightly bigger (due to the re-indentation) > > > but now it handles all the "start at root" in the same place. Doesn't > > > that make sense? > >=20 > > It is correct (though I'd need to clean it up a bit to handle > > nd_jump_root() correctly), and if you really would like me to change it > > I will -- but I just don't agree that it's cleaner. Linus, did you still want me to make your proposed change? --=20 Aleksa Sarai Senior Software Engineer (Containers) SUSE Linux GmbH --i56sxfhksaspu3tw Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iHUEABYIAB0WIQSxZm6dtfE8gxLLfYqdlLljIbnQEgUCXbFNWQAKCRCdlLljIbnQ Ert5AP0aC5CrGCVvHOpelKBjUDOS5duq76VaVyiiUWcy3eeeFwD/aQEQPqkGREqr 5Lo0df+nvE9H+89b7vJGbcaEZNxkTQc= =rtfF -----END PGP SIGNATURE----- --i56sxfhksaspu3tw--