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=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 83FD3CA9EC7 for ; Wed, 30 Oct 2019 23:17:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 551832087E for ; Wed, 30 Oct 2019 23:17:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727617AbfJ3XRr (ORCPT ); Wed, 30 Oct 2019 19:17:47 -0400 Received: from mout-p-201.mailbox.org ([80.241.56.171]:59910 "EHLO mout-p-201.mailbox.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726677AbfJ3XRq (ORCPT ); Wed, 30 Oct 2019 19:17:46 -0400 Received: from smtp2.mailbox.org (smtp2.mailbox.org [80.241.60.241]) (using TLSv1.2 with cipher ECDHE-RSA-CHACHA20-POLY1305 (256/256 bits)) (No client certificate requested) by mout-p-201.mailbox.org (Postfix) with ESMTPS id 473PWC4klPzQk03; Thu, 31 Oct 2019 00:17:43 +0100 (CET) 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 U5HMwcD1nAfE; Thu, 31 Oct 2019 00:17:39 +0100 (CET) Date: Thu, 31 Oct 2019 10:17:31 +1100 From: Aleksa Sarai To: Omar Sandoval Cc: linux-fsdevel@vger.kernel.org, linux-btrfs@vger.kernel.org, Dave Chinner , Jann Horn , linux-api@vger.kernel.org, kernel-team@fb.com Subject: Re: [RFC PATCH v2 1/5] fs: add O_ENCODED open flag Message-ID: <20191030231731.n35rl3d6gss5ura6@yavin.dot.cyphar.com> References: <20191019045057.2fcrzuwc27eg5naf@yavin.dot.cyphar.com> <20191030225540.GG326591@vader> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="jizyjt34uq6bhptu" Content-Disposition: inline In-Reply-To: <20191030225540.GG326591@vader> Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org --jizyjt34uq6bhptu Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On 2019-10-30, Omar Sandoval wrote: > On Sat, Oct 19, 2019 at 03:50:57PM +1100, Aleksa Sarai wrote: > > On 2019-10-15, Omar Sandoval wrote: > > > From: Omar Sandoval > > >=20 > > > The upcoming RWF_ENCODED operation introduces some security concerns: > > >=20 > > > 1. Compressed writes will pass arbitrary data to decompression > > > algorithms in the kernel. > > > 2. Compressed reads can leak truncated/hole punched data. > > >=20 > > > Therefore, we need to require privilege for RWF_ENCODED. It's not > > > possible to do the permissions checks at the time of the read or write > > > because, e.g., io_uring submits IO from a worker thread. So, add an o= pen > > > flag which requires CAP_SYS_ADMIN. It can also be set and cleared with > > > fcntl(). The flag is not cleared in any way on fork or exec; it should > > > probably be used with O_CLOEXEC in most cases. > > >=20 > > > Note that the usual issue that unknown open flags are ignored doesn't > > > really matter for O_ENCODED; if the kernel doesn't support O_ENCODED, > > > then it doesn't support RWF_ENCODED, either. > > >=20 > > > Signed-off-by: Omar Sandoval > > > --- > > > fs/fcntl.c | 10 ++++++++-- > > > fs/namei.c | 4 ++++ > > > include/linux/fcntl.h | 2 +- > > > include/uapi/asm-generic/fcntl.h | 4 ++++ > > > 4 files changed, 17 insertions(+), 3 deletions(-) > > >=20 > > > diff --git a/fs/fcntl.c b/fs/fcntl.c > > > index 3d40771e8e7c..45ebc6df078e 100644 > > > --- a/fs/fcntl.c > > > +++ b/fs/fcntl.c > > > @@ -30,7 +30,8 @@ > > > #include > > > #include > > > =20 > > > -#define SETFL_MASK (O_APPEND | O_NONBLOCK | O_NDELAY | O_DIRECT | O_= NOATIME) > > > +#define SETFL_MASK (O_APPEND | O_NONBLOCK | O_NDELAY | O_DIRECT | O_= NOATIME | \ > > > + O_ENCODED) > > > =20 > > > static int setfl(int fd, struct file * filp, unsigned long arg) > > > { > > > @@ -49,6 +50,11 @@ static int setfl(int fd, struct file * filp, unsig= ned long arg) > > > if (!inode_owner_or_capable(inode)) > > > return -EPERM; > > > =20 > > > + /* O_ENCODED can only be set by superuser */ > > > + if ((arg & O_ENCODED) && !(filp->f_flags & O_ENCODED) && > > > + !capable(CAP_SYS_ADMIN)) > > > + return -EPERM; > >=20 > > I have a feeling the error should probably be an EACCES and not EPERM. >=20 > Shrug, I wanted to make this consistent with O_NOATIME, which uses > EPERM. EACCES seems more appropriate for lacking permissions for a > particular path rather than for an operation, but the lines are blurry. Fair enough, though I would also argue that O_NOATIME should've also been EACCES (and there are plenty of examples throughout the kernel where EPERM was used where EACCES makes more sense). ;) > > > + > > > /* required for strict SunOS emulation */ > > > if (O_NONBLOCK !=3D O_NDELAY) > > > if (arg & O_NDELAY) > > > @@ -1031,7 +1037,7 @@ static int __init fcntl_init(void) > > > * Exceptions: O_NONBLOCK is a two bit define on parisc; O_NDELAY > > > * is defined as O_NONBLOCK on some platforms and not on others. > > > */ > > > - BUILD_BUG_ON(21 - 1 /* for O_RDONLY being 0 */ !=3D > > > + BUILD_BUG_ON(22 - 1 /* for O_RDONLY being 0 */ !=3D > > > HWEIGHT32( > > > (VALID_OPEN_FLAGS & ~(O_NONBLOCK | O_NDELAY)) | > > > __FMODE_EXEC | __FMODE_NONOTIFY)); > > > diff --git a/fs/namei.c b/fs/namei.c > > > index 671c3c1a3425..ae86b125888a 100644 > > > --- a/fs/namei.c > > > +++ b/fs/namei.c > > > @@ -2978,6 +2978,10 @@ static int may_open(const struct path *path, i= nt acc_mode, int flag) > > > if (flag & O_NOATIME && !inode_owner_or_capable(inode)) > > > return -EPERM; > > > =20 > > > + /* O_ENCODED can only be set by superuser */ > > > + if ((flag & O_ENCODED) && !capable(CAP_SYS_ADMIN)) > > > + return -EPERM; > >=20 > > I would suggest that this check be put into build_open_flags() rather > > than putting it this late in open(). Also, same nit about the error > > return as above. >=20 > This is where we check permissions for O_NOATIME, shouldn't we keep all > of those permission checks in the same place? build_open_flags() only > checks for flag validity. Right, but O_NOATIME can't be checked earlier -- you need to have resolved the inode in order to do the permission check. O_ENCODED only depends on the capability set, and IMHO checking it earlier seems cleaner to me. > > > + > > > return 0; > > > } > > > =20 > > > diff --git a/include/linux/fcntl.h b/include/linux/fcntl.h > > > index d019df946cb2..5fac02479639 100644 > > > --- a/include/linux/fcntl.h > > > +++ b/include/linux/fcntl.h > > > @@ -9,7 +9,7 @@ > > > (O_RDONLY | O_WRONLY | O_RDWR | O_CREAT | O_EXCL | O_NOCTTY | O_TRU= NC | \ > > > O_APPEND | O_NDELAY | O_NONBLOCK | O_NDELAY | __O_SYNC | O_DSYNC |= \ > > > FASYNC | O_DIRECT | O_LARGEFILE | O_DIRECTORY | O_NOFOLLOW | \ > > > - O_NOATIME | O_CLOEXEC | O_PATH | __O_TMPFILE) > > > + O_NOATIME | O_CLOEXEC | O_PATH | __O_TMPFILE | O_ENCODED) > > > =20 > > > #ifndef force_o_largefile > > > #define force_o_largefile() (!IS_ENABLED(CONFIG_ARCH_32BIT_OFF_T)) > > > diff --git a/include/uapi/asm-generic/fcntl.h b/include/uapi/asm-gene= ric/fcntl.h > > > index 9dc0bf0c5a6e..8c5cbd5942e3 100644 > > > --- a/include/uapi/asm-generic/fcntl.h > > > +++ b/include/uapi/asm-generic/fcntl.h > > > @@ -97,6 +97,10 @@ > > > #define O_NDELAY O_NONBLOCK > > > #endif > > > =20 > > > +#ifndef O_ENCODED > > > +#define O_ENCODED 040000000 > > > +#endif > >=20 > > You should also define this for all of the architectures which don't use > > the generic O_* flag values. On alpha, O_PATH is equal to the value you > > picked (just be careful on sparc -- 0x4000000 is the next free bit, but > > it's used by FMODE_NONOTIFY.) >=20 > Good catch, I'll fix that. Thanks! Oh, and please add a one-line comment in the sparc header to ensure nobody accidentally breaks open() on sparc in the future. --=20 Aleksa Sarai Senior Software Engineer (Containers) SUSE Linux GmbH --jizyjt34uq6bhptu Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iHUEABYIAB0WIQSxZm6dtfE8gxLLfYqdlLljIbnQEgUCXboaBwAKCRCdlLljIbnQ EvunAQDhTSB4TCQGN6okxxByez30rziSUb/RTyBpIZ9R/yCe5wD/VT/sRb4CLnmt /WSJeuvkF/qTBffr2BFE4fv7KTTizgc= =YDj3 -----END PGP SIGNATURE----- --jizyjt34uq6bhptu--