From: Linus Torvalds <torvalds@linux-foundation.org>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: Aleksa Sarai <cyphar@cyphar.com>,
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: Thu, 9 Jan 2020 16:08:16 -0800 [thread overview]
Message-ID: <CAHk-=wiq11+thoe60qhsSHk_nbRF2TRL1Wnf6eHcYObjhJmsww@mail.gmail.com> (raw)
In-Reply-To: <20200108213444.GF8904@ZenIV.linux.org.uk>
On Wed, Jan 8, 2020 at 1:34 PM Al Viro <viro@zeniv.linux.org.uk> wrote:
>
> The point is, we'd never followed mounts on /proc/self/cwd et.al.
> I hadn't checked 2.0, but 2.1.100 ('97, before any changes from me)
> is that way.
Hmm. If that's the case, maybe they should be marked implicitly as
O_PATH when opened?
> Actually, scratch that - 2.0 behaves the same way
> (mountpoint crossing is done in iget() there; is that Minix influence
> or straight from the Lions' book?)
I don't think I ever had access to Lions' - I've _seen_ a printout of
it later, and obviously maybe others did,
More likely it's from Maurice Bach: the Design of the Unix Operating
System. I'm pretty sure that's where a lot of the FS layer stuff came
from. Certainly the bad old buffer head interfaces, and quite likely
the iget() stuff too.
> 0.10: forward traversal in iget(), back traversal in fs/namei.c:find_entry()
Whee, you _really_ went back in time.
So I did too.
And looking at that code in iget(), I doubt it came from anywhere.
Christ. It's just looping over a fixed-size array, both when finding
the inode, and finding the superblock.
Cute, but unbelievably stupid. It was a more innocent time.
In other words, I think you can chalk it up to just me, because
blaming anybody else for that garbage would be very very unfair indeed
;)
> How would your proposal deal with access("/proc/self/fd/42/foo", MAY_READ)
> vs. faccessat(42, "foo", MAY_READ)?
I think that in a perfect world, the O_PATH'ness of '42' would be the
deciding factor. Wouldn't those be the best and most consistent
semantics?
And then 'cwd'/'root' always have the O_PATH behavior.
> The latter would trigger automount,
> the former would not... Or would you extend that to "traverse mounts
> upon following procfs links, if the file in question had been opened with
> O_PATH"?
Exactly.
But you know what? I do not believe this is all that important, and I
doubt it will matter to anybody.
So what matters most is what makes the most sense to the VFS layer,
and what makes the most sense to _you_.
Because my reaction from this thread is that not only have you thought
about this issue and followed the history a whole lot more than I
would ever have done, it's also that I trust you to DTRT.
I think it would be good to have some self-consistency, but at the
same time clearly we already don't really, and our behavior here has
subtly changed over the years (and not so subtly - if you go back
sufficiently far, /proc behavior wrt file descriptors has had both
"dup()" behavior and "make a new file descriptor with the same inode"
behavior, afaik).
Linus
next prev parent reply other threads:[~2020-01-10 0:08 UTC|newest]
Thread overview: 92+ 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 [this message]
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
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
2020-01-18 12:07 ` [PATCH v3 0/2] openat2: minor uapi cleanups Aleksa Sarai
2020-01-18 12:07 ` [PATCH v3 1/2] open: introduce openat2(2) syscall Aleksa Sarai
2020-01-18 12:08 ` [PATCH v3 2/2] selftests: add openat2(2) selftests Aleksa Sarai
2020-01-18 15:28 ` [PATCH v3 0/2] openat2: minor uapi cleanups Al Viro
2020-01-18 18:09 ` Al Viro
2020-01-18 23:03 ` Aleksa Sarai
2020-01-19 1:12 ` Al Viro
2020-01-15 13:57 ` [PATCH RFC 0/1] mount: universally disallow mounting over symlinks Aleksa Sarai
2020-01-19 3:14 ` [RFC][PATCHSET][CFT] pathwalk cleanups and fixes Al Viro
2020-01-19 3:17 ` [PATCH 01/17] do_add_mount(): lift lock_mount/unlock_mount into callers Al Viro
2020-01-19 3:17 ` [PATCH 02/17] fix automount/automount race properly Al Viro
2020-01-30 14:34 ` Christian Brauner
2020-01-19 3:17 ` [PATCH 03/17] follow_automount(): get rid of dead^Wstillborn code Al Viro
2020-01-30 14:38 ` Christian Brauner
2020-01-19 3:17 ` [PATCH 04/17] follow_automount() doesn't need the entire nameidata Al Viro
2020-01-30 14:45 ` Christian Brauner
2020-01-30 15:38 ` Al Viro
2020-01-30 15:55 ` Al Viro
2020-01-19 3:17 ` [PATCH 05/17] make build_open_flags() treat O_CREAT | O_EXCL as implying O_NOFOLLOW Al Viro
2020-01-19 3:17 ` [PATCH 06/17] handle_mounts(): start building a sane wrapper for follow_managed() Al Viro
2020-01-19 3:17 ` [PATCH 07/17] atomic_open(): saner calling conventions (return dentry on success) Al Viro
2020-01-19 3:17 ` [PATCH 08/17] lookup_open(): " Al Viro
2020-01-19 3:17 ` [PATCH 09/17] do_last(): collapse the call of path_to_nameidata() Al Viro
2020-01-19 3:17 ` [PATCH 10/17] handle_mounts(): pass dentry in, turn path into a pure out argument Al Viro
2020-01-19 3:17 ` [PATCH 11/17] lookup_fast(): consolidate the RCU success case Al Viro
2020-01-19 3:17 ` [PATCH 12/17] teach handle_mounts() to handle RCU mode Al Viro
2020-01-19 3:17 ` [PATCH 13/17] lookup_fast(): take mount traversal into callers Al Viro
2020-01-19 3:17 ` [PATCH 14/17] new step_into() flag: WALK_NOFOLLOW Al Viro
2020-01-19 3:17 ` [PATCH 15/17] fold handle_mounts() into step_into() Al Viro
2020-01-19 3:17 ` [PATCH 16/17] LOOKUP_MOUNTPOINT: fold path_mountpointat() into path_lookupat() Al Viro
2020-01-19 3:17 ` [PATCH 17/17] expand the only remaining call of path_lookup_conditional() Al Viro
2020-01-19 3:17 ` [PATCH 1/9] merging pick_link() with get_link(), part 1 Al Viro
2020-01-19 3:17 ` [PATCH 2/9] merging pick_link() with get_link(), part 2 Al Viro
2020-01-19 3:17 ` [PATCH 3/9] merging pick_link() with get_link(), part 3 Al Viro
2020-01-19 3:17 ` [PATCH 4/9] merging pick_link() with get_link(), part 4 Al Viro
2020-01-19 3:17 ` [PATCH 5/9] merging pick_link() with get_link(), part 5 Al Viro
2020-01-19 3:17 ` [PATCH 6/9] merging pick_link() with get_link(), part 6 Al Viro
2020-01-19 3:17 ` [PATCH 7/9] finally fold get_link() into pick_link() Al Viro
2020-01-19 3:17 ` [PATCH 8/9] massage __follow_mount_rcu() a bit Al Viro
2020-01-19 3:17 ` [PATCH 9/9] new helper: traverse_mounts() Al Viro
2020-01-30 14:13 ` [PATCH 01/17] do_add_mount(): lift lock_mount/unlock_mount into callers Christian Brauner
2020-01-19 14:33 ` [RFC][PATCHSET][CFT] pathwalk cleanups and fixes 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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