From mboxrd@z Thu Jan 1 00:00:00 1970 From: Aleksa Sarai Subject: Re: [PATCH v9 05/10] namei: O_BENEATH-style path resolution flags Date: Tue, 16 Jul 2019 18:03:38 +1000 Message-ID: <20190716080338.al4cnwdfvdbpzh3r@yavin> References: <20190706145737.5299-1-cyphar@cyphar.com> <20190706145737.5299-6-cyphar@cyphar.com> <20190712043341.GI17978@ZenIV.linux.org.uk> <20190712105745.nruaftgeat6irhzr@yavin> <20190712123924.GK17978@ZenIV.linux.org.uk> <20190712125552.GL17978@ZenIV.linux.org.uk> <20190712132553.GN17978@ZenIV.linux.org.uk> <20190712150026.GO17978@ZenIV.linux.org.uk> <20190713024153.GA3817@ZenIV.linux.org.uk> <20190714035826.GQ17978@ZenIV.linux.org.uk> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="lshvdcpckvdb4crm" Return-path: Content-Disposition: inline In-Reply-To: <20190714035826.GQ17978@ZenIV.linux.org.uk> Sender: linux-kernel-owner@vger.kernel.org To: Al Viro Cc: Jeff Layton , "J. Bruce Fields" , Arnd Bergmann , David Howells , Shuah Khan , Shuah Khan , Christian Brauner , David Drysdale , Andy Lutomirski , Linus Torvalds , Eric Biederman , Andrew Morton , Alexei Starovoitov , Kees Cook , Jann Horn , Tycho Andersen , Chanho Min , Oleg Nesterov , Aleksa Sarai , containers@lists.linux-foundation.org, linux-alpha@vger.kernel.org List-Id: linux-api@vger.kernel.org --lshvdcpckvdb4crm Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On 2019-07-14, Al Viro wrote: > On Sat, Jul 13, 2019 at 03:41:53AM +0100, Al Viro wrote: > > On Fri, Jul 12, 2019 at 04:00:26PM +0100, Al Viro wrote: > > > On Fri, Jul 12, 2019 at 02:25:53PM +0100, Al Viro wrote: > > >=20 > > > > if (flags & LOOKUP_BENEATH) { > > > > nd->root =3D nd->path; > > > > if (!(flags & LOOKUP_RCU)) > > > > path_get(&nd->root); > > > > else > > > > nd->root_seq =3D nd->seq; > > >=20 > > > BTW, this assignment is needed for LOOKUP_RCU case. Without it > > > you are pretty much guaranteed that lazy pathwalk will fail, > > > when it comes to complete_walk(). > > >=20 > > > Speaking of which, what would happen if LOOKUP_ROOT/LOOKUP_BENEATH > > > combination would someday get passed? > >=20 > > I don't understand what's going on with ->r_seq in there - your > > call of path_is_under() is after having (re-)sampled rename_lock, > > but if that was the only .. in there, who's going to recheck > > the value? For that matter, what's to guarantee that the thing > > won't get moved just as you are returning from handle_dots()? > >=20 > > IOW, what does LOOKUP_IN_ROOT guarantee for caller (openat2())? >=20 > Sigh... Usual effects of trying to document things: >=20 > 1) LOOKUP_NO_EVAL looks bogus. It had been introduced by commit 57d46577= 16ac > (audit: ignore fcaps on umount) and AFAICS it's crap. It is set in > ksys_umount() and nowhere else. It's ignored by everything except > filename_mountpoint(). The thing is, call graph for filename_mountpoint() > is > filename_mountpoint() > <- user_path_mountpoint_at() > <- ksys_umount() > <- kern_path_mountpoint() > <- autofs_dev_ioctl_ismountpoint() > <- find_autofs_mount() > <- autofs_dev_ioctl_open_mountpoint() > <- autofs_dev_ioctl_requester() > <- autofs_dev_ioctl_ismountpoint() > In other words, that flag is basically "was filename_mountpoint() > been called by umount(2) or has it come from an autofs ioctl?". > And looking at the rationale in that commit, autofs ioctls need > it just as much as umount(2) does. Why is it not set for those > as well? And why is it conditional at all? In addition, LOOKUP_NO_EVAL =3D=3D LOOKUP_OPEN (0x100). Is that meant to be the case? Also I just saw you have a patch in work.namei that fixes this up -- do you want me to rebase on top of that? --=20 Aleksa Sarai Senior Software Engineer (Containers) SUSE Linux GmbH --lshvdcpckvdb4crm Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iHUEABYIAB0WIQSxZm6dtfE8gxLLfYqdlLljIbnQEgUCXS2E1wAKCRCdlLljIbnQ EvUWAP4hDKNKmCaghR/nSF7B9A3mjchQtut9n7vItMKjRPJjLAD9GRABOJCnZ47q TqUSuZfxKfq260PQMTx91hQd/K+//QE= =XoHc -----END PGP SIGNATURE----- --lshvdcpckvdb4crm--