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=-15.0 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=ham 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 AF103C433DF for ; Wed, 12 Aug 2020 01:43:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7C1832054F for ; Wed, 12 Aug 2020 01:43:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726515AbgHLBno (ORCPT ); Tue, 11 Aug 2020 21:43:44 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41836 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726173AbgHLBno (ORCPT ); Tue, 11 Aug 2020 21:43:44 -0400 Received: from mout-p-101.mailbox.org (mout-p-101.mailbox.org [IPv6:2001:67c:2050::465:101]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 04E1EC06174A; Tue, 11 Aug 2020 18:43:44 -0700 (PDT) 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 mout-p-101.mailbox.org (Postfix) with ESMTPS id 4BRCCc5sllzKmjr; Wed, 12 Aug 2020 03:43:40 +0200 (CEST) X-Virus-Scanned: amavisd-new at heinlein-support.de Received: from smtp1.mailbox.org ([80.241.60.240]) by spamfilter06.heinlein-hosting.de (spamfilter06.heinlein-hosting.de [80.241.56.125]) (amavisd-new, port 10030) with ESMTP id MgTaKt_bYsTh; Wed, 12 Aug 2020 03:43:36 +0200 (CEST) Date: Wed, 12 Aug 2020 11:43:24 +1000 From: Aleksa Sarai To: Ross Zwisler Cc: Alexander Viro , linux-kernel@vger.kernel.org, Mattias Nissler , Andrew Morton , Benjamin Gordon , David Howells , Dmitry Torokhov , Jesse Barnes , linux-fsdevel@vger.kernel.org, Matthew Wilcox , Micah Morton , Raul Rangel , Ross Zwisler Subject: Re: [PATCH v7] Add a "nosymfollow" mount option. Message-ID: <20200812014324.rtvlhvopifgkw4mi@yavin.dot.cyphar.com> References: <20200811222803.3224434-1-zwisler@google.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="cin4lu5msomn5ja6" Content-Disposition: inline In-Reply-To: <20200811222803.3224434-1-zwisler@google.com> X-MBO-SPAM-Probability: X-Rspamd-Score: -10.21 / 15.00 / 15.00 X-Rspamd-Queue-Id: 30C491816 X-Rspamd-UID: 9b5518 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --cin4lu5msomn5ja6 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On 2020-08-11, Ross Zwisler wrote: > From: Mattias Nissler >=20 > For mounts that have the new "nosymfollow" option, don't follow symlinks > when resolving paths. The new option is similar in spirit to the > existing "nodev", "noexec", and "nosuid" options, as well as to the > LOOKUP_NO_SYMLINKS resolve flag in the openat2(2) syscall. Various BSD > variants have been supporting the "nosymfollow" mount option for a long > time with equivalent implementations. >=20 > Note that symlinks may still be created on file systems mounted with > the "nosymfollow" option present. readlink() remains functional, so > user space code that is aware of symlinks can still choose to follow > them explicitly. >=20 > Setting the "nosymfollow" mount option helps prevent privileged > writers from modifying files unintentionally in case there is an > unexpected link along the accessed path. The "nosymfollow" option is > thus useful as a defensive measure for systems that need to deal with > untrusted file systems in privileged contexts. >=20 > More information on the history and motivation for this patch can be > found here: >=20 > https://sites.google.com/a/chromium.org/dev/chromium-os/chromiumos-design= -docs/hardening-against-malicious-stateful-data#TOC-Restricting-symlink-tra= versal Looks good. Did you plan to add an in-tree test for this (you could shove it in tools/testing/selftests/mount)? Reviewed-by: Aleksa Sarai > Signed-off-by: Mattias Nissler > Signed-off-by: Ross Zwisler > --- > Changes since v6 [1]: > * Rebased onto v5.8. > * Another round of testing including readlink(1), readlink(2), > realpath(1), realpath(3), statfs(2) and mount(2) to make sure > everything still works. >=20 > After this lands I will upstream changes to util-linux[2] and man-pages > [3]. >=20 > [1]: https://lkml.org/lkml/2020/3/4/770 > [2]: https://github.com/rzwisler/util-linux/commit/7f8771acd85edb70d97921= c026c55e1e724d4e15 > [3]: https://github.com/rzwisler/man-pages/commit/b8fe8079f64b5068940c014= 4586e580399a71668 > --- > fs/namei.c | 3 ++- > fs/namespace.c | 2 ++ > fs/proc_namespace.c | 1 + > fs/statfs.c | 2 ++ > include/linux/mount.h | 3 ++- > include/linux/statfs.h | 1 + > include/uapi/linux/mount.h | 1 + > 7 files changed, 11 insertions(+), 2 deletions(-) >=20 > diff --git a/fs/namei.c b/fs/namei.c > index 72d4219c93acb..ed68478fb1fb6 100644 > --- a/fs/namei.c > +++ b/fs/namei.c > @@ -1626,7 +1626,8 @@ static const char *pick_link(struct nameidata *nd, = struct path *link, > return ERR_PTR(error); > } > =20 > - if (unlikely(nd->flags & LOOKUP_NO_SYMLINKS)) > + if (unlikely(nd->flags & LOOKUP_NO_SYMLINKS) || > + unlikely(nd->path.mnt->mnt_flags & MNT_NOSYMFOLLOW)) > return ERR_PTR(-ELOOP); > =20 > if (!(nd->flags & LOOKUP_RCU)) { > diff --git a/fs/namespace.c b/fs/namespace.c > index 4a0f600a33285..1cbbf5a9b954f 100644 > --- a/fs/namespace.c > +++ b/fs/namespace.c > @@ -3167,6 +3167,8 @@ long do_mount(const char *dev_name, const char __us= er *dir_name, > mnt_flags &=3D ~(MNT_RELATIME | MNT_NOATIME); > if (flags & MS_RDONLY) > mnt_flags |=3D MNT_READONLY; > + if (flags & MS_NOSYMFOLLOW) > + mnt_flags |=3D MNT_NOSYMFOLLOW; > =20 > /* The default atime for remount is preservation */ > if ((flags & MS_REMOUNT) && > diff --git a/fs/proc_namespace.c b/fs/proc_namespace.c > index 3059a9394c2d6..e59d4bb3a89e4 100644 > --- a/fs/proc_namespace.c > +++ b/fs/proc_namespace.c > @@ -70,6 +70,7 @@ static void show_mnt_opts(struct seq_file *m, struct vf= smount *mnt) > { MNT_NOATIME, ",noatime" }, > { MNT_NODIRATIME, ",nodiratime" }, > { MNT_RELATIME, ",relatime" }, > + { MNT_NOSYMFOLLOW, ",nosymfollow" }, > { 0, NULL } > }; > const struct proc_fs_opts *fs_infop; > diff --git a/fs/statfs.c b/fs/statfs.c > index 2616424012ea7..59f33752c1311 100644 > --- a/fs/statfs.c > +++ b/fs/statfs.c > @@ -29,6 +29,8 @@ static int flags_by_mnt(int mnt_flags) > flags |=3D ST_NODIRATIME; > if (mnt_flags & MNT_RELATIME) > flags |=3D ST_RELATIME; > + if (mnt_flags & MNT_NOSYMFOLLOW) > + flags |=3D ST_NOSYMFOLLOW; > return flags; > } > =20 > diff --git a/include/linux/mount.h b/include/linux/mount.h > index de657bd211fa6..aaf343b38671c 100644 > --- a/include/linux/mount.h > +++ b/include/linux/mount.h > @@ -30,6 +30,7 @@ struct fs_context; > #define MNT_NODIRATIME 0x10 > #define MNT_RELATIME 0x20 > #define MNT_READONLY 0x40 /* does the user want this to be r/o? */ > +#define MNT_NOSYMFOLLOW 0x80 > =20 > #define MNT_SHRINKABLE 0x100 > #define MNT_WRITE_HOLD 0x200 > @@ -46,7 +47,7 @@ struct fs_context; > #define MNT_SHARED_MASK (MNT_UNBINDABLE) > #define MNT_USER_SETTABLE_MASK (MNT_NOSUID | MNT_NODEV | MNT_NOEXEC \ > | MNT_NOATIME | MNT_NODIRATIME | MNT_RELATIME \ > - | MNT_READONLY) > + | MNT_READONLY | MNT_NOSYMFOLLOW) > #define MNT_ATIME_MASK (MNT_NOATIME | MNT_NODIRATIME | MNT_RELATIME ) > =20 > #define MNT_INTERNAL_FLAGS (MNT_SHARED | MNT_WRITE_HOLD | MNT_INTERNAL |= \ > diff --git a/include/linux/statfs.h b/include/linux/statfs.h > index 9bc69edb8f188..fac4356ea1bfc 100644 > --- a/include/linux/statfs.h > +++ b/include/linux/statfs.h > @@ -40,6 +40,7 @@ struct kstatfs { > #define ST_NOATIME 0x0400 /* do not update access times */ > #define ST_NODIRATIME 0x0800 /* do not update directory access times */ > #define ST_RELATIME 0x1000 /* update atime relative to mtime/ctime */ > +#define ST_NOSYMFOLLOW 0x2000 /* do not follow symlinks */ > =20 > struct dentry; > extern int vfs_get_fsid(struct dentry *dentry, __kernel_fsid_t *fsid); > diff --git a/include/uapi/linux/mount.h b/include/uapi/linux/mount.h > index 96a0240f23fed..dd8306ea336c1 100644 > --- a/include/uapi/linux/mount.h > +++ b/include/uapi/linux/mount.h > @@ -16,6 +16,7 @@ > #define MS_REMOUNT 32 /* Alter flags of a mounted FS */ > #define MS_MANDLOCK 64 /* Allow mandatory locks on an FS */ > #define MS_DIRSYNC 128 /* Directory modifications are synchronous */ > +#define MS_NOSYMFOLLOW 256 /* Do not follow symlinks */ > #define MS_NOATIME 1024 /* Do not update access times. */ > #define MS_NODIRATIME 2048 /* Do not update directory access times */ > #define MS_BIND 4096 > --=20 > 2.28.0.236.gb10cc79966-goog >=20 --=20 Aleksa Sarai Senior Software Engineer (Containers) SUSE Linux GmbH --cin4lu5msomn5ja6 Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iHUEABYIAB0WIQSxZm6dtfE8gxLLfYqdlLljIbnQEgUCXzNJLQAKCRCdlLljIbnQ EsDjAQDDwisyM9fOuV+Ed0MJ00dzw040RQ7+LVK/5aoQkBbRmQEAr67/mlNPDrRB npO+QCicLL7SvDb22zFE3wueer23Hwk= =Fd7y -----END PGP SIGNATURE----- --cin4lu5msomn5ja6--