From: Aleksa Sarai <cyphar@cyphar.com>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-ia64@vger.kernel.org, linux-sh@vger.kernel.org,
Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
Alexei Starovoitov <ast@kernel.org>,
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linux-kselftest@vger.kernel.org, sparclinux@vger.kernel.org,
Shuah Khan <shuah@kernel.org>,
raven@themaw.net, linux-arch@vger.kernel.org,
linux-s390@vger.kernel.org, Tycho Andersen <tycho@tycho.ws>,
paul@paul-moore.com, Aleksa Sarai <asarai@suse.de>,
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linux-xtensa@linux-xtensa.org, Kees Cook <keescook@chromium.org>,
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linuxppc-dev@lists.ozlabs.org, linux-m68k@lists.linux-m68k.org,
Andy Lutomirski <luto@kernel.org>,
Shuah Khan <skhan@linuxfoundation.org>,
David Drysdale <drysdale@google.com>,
Christian Brauner <christian@brauner.io>,
"J. Bruce Fields" <bfields@fieldses.org>,
linux-parisc@vger.kernel.org, rgb@redhat.com,
linux-api@vger.kernel.org, Chanho Min <chanho.min@lge.com>,
Jeff Layton <jlayton@kernel.org>, Oleg Nesterov <oleg@redhat.com>,
Eric Biederman <ebiederm@xmission.com>,
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Andrew Morton <akpm@linux-foundation.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
containers@lists.linux-foundation.org
Subject: Re: [PATCH v9 05/10] namei: O_BENEATH-style path resolution flags
Date: Tue, 16 Jul 2019 18:03:38 +1000 [thread overview]
Message-ID: <20190716080338.al4cnwdfvdbpzh3r@yavin> (raw)
In-Reply-To: <20190714035826.GQ17978@ZenIV.linux.org.uk>
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On 2019-07-14, Al Viro <viro@zeniv.linux.org.uk> 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:
> > >
> > > > if (flags & LOOKUP_BENEATH) {
> > > > nd->root = nd->path;
> > > > if (!(flags & LOOKUP_RCU))
> > > > path_get(&nd->root);
> > > > else
> > > > nd->root_seq = nd->seq;
> > >
> > > 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().
> > >
> > > Speaking of which, what would happen if LOOKUP_ROOT/LOOKUP_BENEATH
> > > combination would someday get passed?
> >
> > 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()?
> >
> > IOW, what does LOOKUP_IN_ROOT guarantee for caller (openat2())?
>
> Sigh... Usual effects of trying to document things:
>
> 1) LOOKUP_NO_EVAL looks bogus. It had been introduced by commit 57d4657716ac
> (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 == 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?
--
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
<https://www.cyphar.com/>
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next prev parent reply other threads:[~2019-07-16 8:04 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-06 14:57 [PATCH v9 00/10] namei: openat2(2) path resolution restrictions Aleksa Sarai
2019-07-06 14:57 ` [PATCH v9 01/10] namei: obey trailing magic-link DAC permissions Aleksa Sarai
2019-07-12 4:14 ` Al Viro
2019-07-12 6:36 ` Al Viro
2019-07-12 12:20 ` Aleksa Sarai
2019-07-12 13:10 ` Al Viro
2019-07-14 7:11 ` Aleksa Sarai
2019-07-06 14:57 ` [PATCH v9 02/10] procfs: switch magic-link modes to be more sane Aleksa Sarai
2019-07-06 14:57 ` [PATCH v9 03/10] open: O_EMPTYPATH: procfs-less file descriptor re-opening Aleksa Sarai
2019-07-06 14:57 ` [PATCH v9 04/10] namei: split out nd->dfd handling to dirfd_path_init Aleksa Sarai
2019-07-12 4:20 ` Al Viro
2019-07-12 12:07 ` Aleksa Sarai
2019-07-12 12:12 ` Aleksa Sarai
2019-07-06 14:57 ` [PATCH v9 05/10] namei: O_BENEATH-style path resolution flags Aleksa Sarai
2019-07-12 4:33 ` Al Viro
2019-07-12 10:57 ` Aleksa Sarai
2019-07-12 12:39 ` Al Viro
2019-07-12 12:55 ` Al Viro
2019-07-12 13:25 ` Al Viro
2019-07-12 15:00 ` Al Viro
2019-07-13 2:41 ` Al Viro
2019-07-14 3:58 ` Al Viro
2019-07-16 8:03 ` Aleksa Sarai [this message]
2019-07-14 7:00 ` Aleksa Sarai
2019-07-14 14:36 ` Al Viro
2019-07-18 3:17 ` Aleksa Sarai
2019-07-14 10:31 ` Aleksa Sarai
2019-07-06 14:57 ` [PATCH v9 06/10] namei: LOOKUP_IN_ROOT: chroot-like path resolution Aleksa Sarai
2019-07-06 14:57 ` [PATCH v9 07/10] namei: aggressively check for nd->root escape on ".." resolution Aleksa Sarai
2019-07-06 14:57 ` [PATCH v9 08/10] open: openat2(2) syscall Aleksa Sarai
2019-07-18 14:48 ` Rasmus Villemoes
2019-07-18 15:21 ` Aleksa Sarai
2019-07-18 15:10 ` Arnd Bergmann
2019-07-18 16:12 ` Aleksa Sarai
2019-07-18 21:29 ` Arnd Bergmann
2019-07-19 2:12 ` Dmitry V. Levin
2019-07-19 10:29 ` Christian Brauner
2019-07-19 1:59 ` Dmitry V. Levin
2019-07-19 2:19 ` Aleksa Sarai
2019-07-06 14:57 ` [PATCH v9 09/10] kselftest: save-and-restore errno to allow for %m formatting Aleksa Sarai
2019-07-06 14:57 ` [PATCH v9 10/10] selftests: add openat2(2) selftests Aleksa Sarai
2019-07-08 1:15 ` Michael Ellerman
2019-07-08 5:47 ` Aleksa Sarai
2019-07-12 15:11 ` [PATCH v9 00/10] namei: openat2(2) path resolution restrictions Al Viro
2019-07-12 15:32 ` Aleksa Sarai
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