From: Al Viro <viro@zeniv.linux.org.uk>
To: Aleksa Sarai <cyphar@cyphar.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
David Howells <dhowells@redhat.com>,
Eric Biederman <ebiederm@xmission.com>,
stable <stable@vger.kernel.org>,
Christian Brauner <christian.brauner@ubuntu.com>,
Serge Hallyn <serge@hallyn.com>,
dev@opencontainers.org,
Linux Containers <containers@lists.linux-foundation.org>,
Linux API <linux-api@vger.kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Ian Kent <raven@themaw.net>
Subject: Re: [PATCH RFC 0/1] mount: universally disallow mounting over symlinks
Date: Tue, 14 Jan 2020 04:57:33 +0000 [thread overview]
Message-ID: <20200114045733.GW8904@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20200110210719.ktg3l2kwjrdutlh6@yavin>
On Sat, Jan 11, 2020 at 08:07:19AM +1100, Aleksa Sarai wrote:
> If I'm understanding this proposal correctly, this would be a problem
> for the libpathrs use-case -- if this is done then there's no way to
> avoid a TOCTOU with someone mounting and the userspace program checking
> whether something is a mountpoint (unless you have Linux >5.6 and
> RESOLVE_NO_XDEV). Today, you can (in theory) do it with MNT_EXPIRE:
>
> 1. Open the candidate directory.
> 2. umount2(MNT_EXPIRE) the fd.
> * -EINVAL means it wasn't a mountpoint when we got the fd, and the
> fd is a stable handle to the underlying directory.
> * -EAGAIN or -EBUSY means that it was a mountpoint or became a
> mountpoint after the fd was opened (we don't care about that, but
> fail-safe is better here).
> 3. Use the fd from (1) for all operations.
... except that foo/../bar *WILL* cross into the covering mount, on any
kernel that supports ...at(2) at all, so I would be very cautious about
any kind "hardening" claims in that case.
I'm not sure about Linus' proposal - it looks rather convoluted and we
get a hard to describe twist of semantics in an area (procfs symlinks
vs. mount traversal) on top of everything else in there...
Anyway, a couple of questions:
1) do you see any problems on your testcases with the current #fixes?
That's commit 7a955b7363b8 as branch tip.
2) do you have any updates you would like to fold into stuff in
#work.openat2? Right now I have a local variant of #work.namei (with
fairly cosmetical change compared to vfs.git one) that merges clean
with #work.openat2; I would like to do any updates/fold-ins/etc.
of #work.openat2 *before* doing a merge and continuing to work on
top of the merge results...
next prev parent reply other threads:[~2020-01-14 4:57 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-30 5:20 [PATCH RFC 0/1] mount: universally disallow mounting over symlinks Aleksa Sarai
2019-12-30 5:20 ` [PATCH RFC 1/1] " Aleksa Sarai
2019-12-30 7:34 ` Linus Torvalds
2019-12-30 8:28 ` Aleksa Sarai
2020-01-08 4:39 ` Andy Lutomirski
2019-12-30 5:44 ` [PATCH RFC 0/1] " Al Viro
2019-12-30 5:49 ` Aleksa Sarai
2019-12-30 7:29 ` Aleksa Sarai
2019-12-30 7:53 ` Linus Torvalds
2019-12-30 8:32 ` Aleksa Sarai
2020-01-02 8:58 ` David Laight
2020-01-02 9:09 ` Aleksa Sarai
2020-01-01 0:43 ` Al Viro
2020-01-01 0:54 ` Al Viro
2020-01-01 3:08 ` Al Viro
2020-01-01 14:44 ` Aleksa Sarai
2020-01-01 23:40 ` Al Viro
2020-01-02 3:59 ` Aleksa Sarai
2020-01-03 1:49 ` Al Viro
2020-01-04 4:46 ` Ian Kent
2020-01-08 3:13 ` Al Viro
2020-01-08 3:54 ` Linus Torvalds
2020-01-08 21:34 ` Al Viro
2020-01-10 0:08 ` Linus Torvalds
2020-01-10 4:15 ` Al Viro
2020-01-10 5:03 ` Linus Torvalds
2020-01-10 6:20 ` Ian Kent
2020-01-12 21:33 ` Al Viro
2020-01-13 2:59 ` Ian Kent
2020-01-14 0:25 ` Ian Kent
2020-01-14 4:39 ` Al Viro
2020-01-14 5:01 ` Ian Kent
2020-01-14 5:59 ` Ian Kent
2020-01-10 21:07 ` Aleksa Sarai
2020-01-14 4:57 ` Al Viro [this message]
2020-01-14 5:12 ` Al Viro
2020-01-14 20:01 ` Aleksa Sarai
2020-01-15 14:25 ` Al Viro
2020-01-15 14:29 ` Aleksa Sarai
2020-01-15 14:34 ` Aleksa Sarai
2020-01-15 14:48 ` Al Viro
2020-01-15 13:57 ` Aleksa Sarai
2020-01-19 3:14 ` [RFC][PATCHSET][CFT] pathwalk cleanups and fixes Al Viro
2020-01-19 14:33 ` Ian Kent
2020-01-10 23:19 ` [PATCH RFC 0/1] mount: universally disallow mounting over symlinks Al Viro
2020-01-13 1:48 ` Ian Kent
2020-01-13 3:54 ` Al Viro
2020-01-13 6:00 ` Ian Kent
2020-01-13 6:03 ` Ian Kent
2020-01-13 13:30 ` Al Viro
2020-01-14 7:25 ` Ian Kent
2020-01-14 12:17 ` Ian Kent
2020-01-04 5:52 ` Andy Lutomirski
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