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,
Alexei Starovoitov <ast@kernel.org>,
linux-kernel@vger.kernel.org, David Howells <dhowells@redhat.com>,
linux-kselftest@vger.kernel.org, sparclinux@vger.kernel.org,
Shuah Khan <shuah@kernel.org>,
linux-arch@vger.kernel.org, linux-s390@vger.kernel.org,
Tycho Andersen <tycho@tycho.ws>, Aleksa Sarai <asarai@suse.de>,
linux-arm-kernel@lists.infradead.org, linux-mips@vger.kernel.org,
linux-xtensa@linux-xtensa.org, Kees Cook <keescook@chromium.org>,
Arnd Bergmann <arnd@arndb.de>, Jann Horn <jannh@google.com>,
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, 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>,
linux-alpha@vger.kernel.org, linux-fsdevel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
containers@lists.linux-foundation.org
Subject: Re: [PATCH v9 01/10] namei: obey trailing magic-link DAC permissions
Date: Sun, 14 Jul 2019 17:11:02 +1000 [thread overview]
Message-ID: <20190714071102.gsc3kqpakz7chqt6@yavin> (raw)
In-Reply-To: <20190712131005.GM17978@ZenIV.linux.org.uk>
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On 2019-07-12, Al Viro <viro@zeniv.linux.org.uk> wrote:
> On Fri, Jul 12, 2019 at 10:20:17PM +1000, Aleksa Sarai wrote:
> > On 2019-07-12, Al Viro <viro@zeniv.linux.org.uk> wrote:
> > > On Sun, Jul 07, 2019 at 12:57:28AM +1000, Aleksa Sarai wrote:
> > > > @@ -514,7 +516,14 @@ static void set_nameidata(struct nameidata *p, int dfd, struct filename *name)
> > > > p->stack = p->internal;
> > > > p->dfd = dfd;
> > > > p->name = name;
> > > > - p->total_link_count = old ? old->total_link_count : 0;
> > > > + p->total_link_count = 0;
> > > > + p->acc_mode = 0;
> > > > + p->opath_mask = FMODE_PATH_READ | FMODE_PATH_WRITE;
> > > > + if (old) {
> > > > + p->total_link_count = old->total_link_count;
> > > > + p->acc_mode = old->acc_mode;
> > > > + p->opath_mask = old->opath_mask;
> > > > + }
> > >
> > > Huh? Could somebody explain why traversals of NFS4 referrals should inherit
> > > ->acc_mode and ->opath_mask?
> >
> > I'll be honest -- I don't understand what set_nameidata() did so I just
> > did what I thought would be an obvious change (to just copy the
> > contents). I thought it was related to some aspect of the symlink stack
> > handling.
>
> No. It's handling of (very rare) nested pathwalk. The only case I can think
> of is handling of NFS4 referrals - they are triggered by ->d_automount()
> and include NFS4 mount. Which does internal pathwalk of its own, to get
> to the root of subtree being automounted.
>
> NFS has its own recursion protection on that path (no deeper nesting than
> one level of referral traversals), but there some nesting is inevitable;
> we do get another nameidata instance on stack. And for nd_jump_link() we
> need to keep track of the innermost one.
>
> For symlinks nothing of that sort happens - they are dealt with on the same
> struct nameidata. ->total_link_count copying is there for one reason only -
> we want the total amount of symlinks traversed during the pathwalk (including
> the referral processing, etc.) to count towards MAXSYMLINKS check. It could've
> been moved from nameidata to task_struct, but it's cheaper to handle it that
> way.
>
> Again, nesting is *rare*.
Thanks for the explanation, much appreciated. I will drop the old->...
copying hunk.
> > In that case, should they both be set to 0 on set_nameidata()? This will
> > mean that fd re-opening (or magic-link opening) through a
> > set_nameidata() would always fail.
>
> Huh? set_nameidata() is done for *all* instances - it's pretty much the
> constructor of that object (and restore_nameidata() - a destructor).
> Everything goes through it.
Sorry, I meant to drop the copy-from-old logic -- not set it to zero
explicitly in set_nameidata().
> And again, I'm not sure we want these fields in nameidata - IMO they belong
> in open_flags. Things like e.g. stat() don't need them at all.
Yup, I'll work up a version that does the consolidation you mentioned
in your other mail.
> Incidentally, O_PATH opening of symlinks combined with subsequent procfs
> symlink traversals is worth testing - that's where the things get subtle
> and that's where it's easy to get in trouble on modifications.
I have some self-tests of a symlink-to-a-magic-link in the last patch of
the series. Did you mean something even more chained like a symlink to a
/proc/self/fd/$n of an O_NOFOLLOW|O_PATH of a symlink?
--
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
<https://www.cyphar.com/>
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next prev parent reply other threads:[~2019-07-14 7:11 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 [this message]
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
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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