From: "Jürg Billeter" <j@bitron.ch>
To: Aleksa Sarai <cyphar@cyphar.com>,
Al Viro <viro@zeniv.linux.org.uk>,
Jeff Layton <jlayton@kernel.org>,
"J. Bruce Fields" <bfields@fieldses.org>,
Arnd Bergmann <arnd@arndb.de>,
David Howells <dhowells@redhat.com>
Cc: Eric Biederman <ebiederm@xmission.com>,
Christian Brauner <christian@brauner.io>,
linux-api@vger.kernel.org, Andy Lutomirski <luto@kernel.org>,
Jann Horn <jannh@google.com>,
David Drysdale <drysdale@google.com>,
Aleksa Sarai <asarai@suse.de>,
containers@lists.linux-foundation.org,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-arch@vger.kernel.org
Subject: Re: [PATCH v4 2/4] namei: O_BENEATH-style path resolution flags
Date: Fri, 23 Nov 2018 13:10:17 +0100 [thread overview]
Message-ID: <1ce83cdf6e3168350b69f98f08aaa202bbaa682d.camel@bitron.ch> (raw)
In-Reply-To: <20181112142654.341-3-cyphar@cyphar.com>
Hi Aleksa,
On Tue, 2018-11-13 at 01:26 +1100, Aleksa Sarai wrote:
> * O_BENEATH: Disallow "escapes" from the starting point of the
> filesystem tree during resolution (you must stay "beneath" the
> starting point at all times). Currently this is done by disallowing
> ".." and absolute paths (either in the given path or found during
> symlink resolution) entirely, as well as all "magic link" jumping.
With open_tree(2) and OPEN_TREE_CLONE, will O_BENEATH still be
necessary? As I understand it, O_BENEATH could be replaced by a much
simpler flag that only disallows absolute paths (incl. absolute
symlinks). And it would have the benefit that you can actually pass the
tree/directory fd to another process and escaping would not be possible
even if that other process doesn't use O_BENEATH (after calling
mount_setattr(2) to make sure it's locked down).
This approach would also make it easy to restrict writes via a cloned
tree/directory fd by marking it read-only via mount_setattr(2) (and
locking down the read-only flag). This would again be especially useful
when passing tree/directory fds across processes, or for voluntary
self-lockdown within a process for robustness against security bugs.
This wouldn't affect any of the other flags in this patch. And for full
equivalence to O_BENEATH you'd have to use O_NOMAGICLINKS in addition
to O_NOABSOLUTE, or whatever that new flag would be called.
Or is OPEN_TREE_CLONE too expensive for this use case? Or is there
anything else I'm missing?
Jürg
next prev parent reply other threads:[~2018-11-23 23:04 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-12 14:26 [PATCH v4 0/4] namei: O_* flags to restrict path resolution Aleksa Sarai
2018-11-12 14:26 ` [PATCH v4 1/4] namei: split out nd->dfd handling to dirfd_path_init Aleksa Sarai
2018-11-12 14:26 ` [PATCH v4 2/4] namei: O_BENEATH-style path resolution flags Aleksa Sarai
2018-11-23 12:10 ` Jürg Billeter [this message]
2018-11-23 16:07 ` Andy Lutomirski
2018-11-23 16:48 ` Aleksa Sarai
2018-11-23 16:52 ` Aleksa Sarai
2018-11-23 16:58 ` Aleksa Sarai
2018-11-12 14:26 ` [PATCH v4 3/4] namei: O_THISROOT: chroot-like path resolution Aleksa Sarai
2018-11-12 14:26 ` [PATCH v4 4/4] namei: aggressively check for nd->root escape on ".." resolution Aleksa Sarai
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1ce83cdf6e3168350b69f98f08aaa202bbaa682d.camel@bitron.ch \
--to=j@bitron.ch \
--cc=arnd@arndb.de \
--cc=asarai@suse.de \
--cc=bfields@fieldses.org \
--cc=christian@brauner.io \
--cc=containers@lists.linux-foundation.org \
--cc=cyphar@cyphar.com \
--cc=dhowells@redhat.com \
--cc=drysdale@google.com \
--cc=ebiederm@xmission.com \
--cc=jannh@google.com \
--cc=jlayton@kernel.org \
--cc=linux-api@vger.kernel.org \
--cc=linux-arch@vger.kernel.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=luto@kernel.org \
--cc=viro@zeniv.linux.org.uk \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).