linux-kernel - Re: [PATCH v2 00/10] allow unprivileged overlay mounts

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Message-ID: <1725e01a-4d4d-aecb-bad6-54aa220b4cd2@i-love.sakura.ne.jp>
Date:   Tue, 8 Dec 2020 19:27:13 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Miklos Szeredi <mszeredi@...hat.com>,
        "Eric W . Biederman" <ebiederm@...ssion.com>
Cc:     linux-fsdevel@...r.kernel.org, linux-unionfs@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        John Johansen <john.johansen@...onical.com>
Subject: Re: [PATCH v2 00/10] allow unprivileged overlay mounts

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.