From: Al Viro <viro@zeniv.linux.org.uk>
To: Aleksa Sarai <cyphar@cyphar.com>
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: Fri, 12 Jul 2019 05:14:54 +0100 [thread overview]
Message-ID: <20190712041454.GG17978@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20190706145737.5299-2-cyphar@cyphar.com>
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?
> static __always_inline
> -const char *get_link(struct nameidata *nd)
> +const char *get_link(struct nameidata *nd, bool trailing)
> {
> struct saved *last = nd->stack + nd->depth - 1;
> struct dentry *dentry = last->link.dentry;
> @@ -1081,6 +1134,44 @@ const char *get_link(struct nameidata *nd)
> } else {
> res = get(dentry, inode, &last->done);
> }
> + /* If we just jumped it was because of a magic-link. */
> + if (unlikely(nd->flags & LOOKUP_JUMPED)) {
That's not quite guaranteed (it is possible to bind a symlink on top
of a regular file, and you will get LOOKUP_JUMPED on the entry into
trailing_symlink() when looking the result up). Moreover, why bother
with LOOKUP_JUMPED here? See that
nd->last_type = LAST_BIND;
several lines prior? That's precisely to be able to recognize those
suckers.
And _that_ would've avoided another piece of ugliness - your LOOKUP_JUMPED
kludge forces you to handle that cra^Wsclero^Wvaluable security hardening
in get_link(), instead of trailing_symlink() where you apparently want
it to be. Simply because nd_jump_root() done later in get_link() will set
LOOKUP_JUMPED for absolute symlinks, confusing your test.
Moreover, I'm not sure that trailing_symlink() is the right place for
that either - I would be rather tempted to fold do_o_path() into
path_openat(), inline path_lookupat() there (as in
s = path_init(nd, flags);
while (!(error = link_path_walk(s, nd))
&& ((error = lookup_last(nd)) > 0)) {
s = trailing_symlink(nd);
}
if (!error)
error = complete_walk(nd);
if (!error && nd->flags & LOOKUP_DIRECTORY)
if (!d_can_lookup(nd->path.dentry))
error = -ENOTDIR;
if (!error) {
audit_inode(nd->name, nd->path.dentry, 0);
error = vfs_open(&nd->path, file);
}
terminate_walk(nd);
- we don't need LOOKUP_DOWN there) and then we only care about the
two callers of trailing_symlink() that are in path_openat(). Which
is where you have your ->acc_mode and ->opath_mask without the need
to dump them into nameidata. Or to bring that mess into the
things like stat(2) et.al. - it simply doesn't belong there.
In any case, this "bool trailing" is completely wrong; whether that
check belongs in trailing_symlink() or (some of) its callers, putting
it into get_link() is a mistake, forced by kludgy check for procfs-style
symlinks.
next prev parent reply other threads:[~2019-07-12 4:17 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 [this message]
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
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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