From: John Johansen <john.johansen@canonical.com>
To: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
Miklos Szeredi <mszeredi@redhat.com>,
"Eric W . Biederman" <ebiederm@xmission.com>
Cc: linux-fsdevel@vger.kernel.org, linux-unionfs@vger.kernel.org,
linux-security-module@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 00/10] allow unprivileged overlay mounts
Date: Thu, 10 Dec 2020 00:56:32 -0800 [thread overview]
Message-ID: <7a64acab-dd05-765f-df2c-4896eb6a29df@canonical.com> (raw)
In-Reply-To: <1725e01a-4d4d-aecb-bad6-54aa220b4cd2@i-love.sakura.ne.jp>
On 12/8/20 2:27 AM, Tetsuo Handa wrote:
> On 2020/12/08 1:32, Miklos Szeredi wrote:
>> A general observation is that overlayfs does not call security_path_*()
>> hooks on the underlying fs. I don't see this as a problem, because a
>> simple bind mount done inside a private mount namespace also defeats the
>> path based security checks. Maybe I'm missing something here, so I'm
>> interested in comments from AppArmor and Tomoyo developers.
>
> Regarding TOMOYO, I don't want overlayfs to call security_path_*() hooks on the
> underlying fs, but the reason is different. It is not because a simple bind mount
> done inside a private mount namespace defeats the path based security checks.
> TOMOYO does want to check what device/filesystem is mounted on which location. But
> currently TOMOYO is failing to check it due to fsopen()/fsmount()/move_mount() API.
>
Regardless of TOMOYO's approach I would say that overlays should call the
security_path_*() hooks, making it possible for an LSM to do something based off of
them when needed.
The current state of private mounts with regard to path based mediation is broken.
I just haven't had time to try and come up with an acceptable fix for it. overlayfs
is actually broken under apparmor mediation, and accesses to the lower layer end up
getting denied but there is no way to properly allow them. So policy that hits this
needs a flag set that allows for it in a very hacky way (its on the list of things
to fix).
Path based mediation has to carefully control mounts otherwise policy can be
circumvented as Miklos rightly points out. Ideally path based LSM wouldn't allow
you to do the simple bind mount inside a private mount namespace (at least not
unless policy allowed for it). AppArmor does mediate the mount hooks and bind
mounts in a private mount namespace (if they go through the LSM mount hooks) will
be denied. Again the problem is how to allow them, and this is broken.
next prev parent reply other threads:[~2020-12-10 8:57 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-07 16:32 [PATCH v2 00/10] allow unprivileged overlay mounts Miklos Szeredi
2020-12-07 16:32 ` [PATCH v2 01/10] vfs: move cap_convert_nscap() call into vfs_setxattr() Miklos Szeredi
2020-12-09 1:53 ` James Morris
2021-01-01 17:35 ` Eric W. Biederman
2021-01-11 13:49 ` Miklos Szeredi
2021-01-12 0:14 ` Eric W. Biederman
2021-01-12 9:43 ` Miklos Szeredi
2021-01-12 10:04 ` Miklos Szeredi
2021-01-12 18:36 ` Eric W. Biederman
2021-01-12 18:49 ` Eric W. Biederman
2020-12-07 16:32 ` [PATCH v2 02/10] vfs: verify source area in vfs_dedupe_file_range_one() Miklos Szeredi
2020-12-07 16:32 ` [PATCH v2 03/10] ovl: check privs before decoding file handle Miklos Szeredi
2020-12-08 13:49 ` Amir Goldstein
2020-12-09 10:13 ` Miklos Szeredi
2020-12-09 16:20 ` Miklos Szeredi
2020-12-09 18:16 ` Amir Goldstein
2020-12-07 16:32 ` [PATCH v2 04/10] ovl: make ioctl() safe Miklos Szeredi
2020-12-08 11:11 ` Amir Goldstein
2020-12-10 15:18 ` Miklos Szeredi
2020-12-14 5:44 ` Amir Goldstein
2020-12-14 13:23 ` Miklos Szeredi
2020-12-14 14:47 ` Amir Goldstein
2020-12-09 1:57 ` James Morris
2020-12-10 15:19 ` Miklos Szeredi
2020-12-07 16:32 ` [PATCH v2 05/10] ovl: simplify file splice Miklos Szeredi
2020-12-07 16:32 ` [PATCH v2 06/10] ovl: user xattr Miklos Szeredi
2020-12-08 13:10 ` Amir Goldstein
2020-12-11 14:55 ` Miklos Szeredi
2020-12-07 16:32 ` [PATCH v2 07/10] ovl: do not fail when setting origin xattr Miklos Szeredi
2020-12-07 16:32 ` [PATCH v2 08/10] ovl: do not fail because of O_NOATIME Miklos Szeredi
2020-12-08 11:29 ` Amir Goldstein
2020-12-11 14:44 ` Miklos Szeredi
2020-12-14 5:49 ` Amir Goldstein
2020-12-07 16:32 ` [PATCH v2 09/10] ovl: do not get metacopy for userxattr Miklos Szeredi
2020-12-07 16:32 ` [PATCH v2 10/10] ovl: unprivieged mounts Miklos Szeredi
2020-12-08 10:27 ` [PATCH v2 00/10] allow unprivileged overlay mounts Tetsuo Handa
2020-12-10 8:56 ` John Johansen [this message]
2020-12-10 9:39 ` Miklos Szeredi
2020-12-15 11:03 ` John Johansen
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