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Subject: Re: BUG: Mount ignores mount options
From:   Andy Lutomirski <luto@amacapital.net>
In-Reply-To: <87d0uqpba5.fsf@xmission.com>
Date:   Fri, 10 Aug 2018 07:36:17 -0700
Cc:     David Howells <dhowells@redhat.com>, viro@zeniv.linux.org.uk,
        John Johansen <john.johansen@canonical.com>,
        Tejun Heo <tj@kernel.org>, selinux@tycho.nsa.gov,
        Paul Moore <paul@paul-moore.com>,
        Li Zefan <lizefan@huawei.com>, linux-api@vger.kernel.org,
        apparmor@lists.ubuntu.com,
        Casey Schaufler <casey@schaufler-ca.com>, fenghua.yu@intel.com,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Eric Biggers <ebiggers@google.com>,
        linux-security-module@vger.kernel.org,
        Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Stephen Smalley <sds@tycho.nsa.gov>,
        tomoyo-dev-en@lists.sourceforge.jp, cgroups@vger.kernel.org,
        torvalds@linux-foundation.org, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org, "Theodore Y. Ts'o" <tytso@mit.edu>,
        Miklos Szeredi <miklos@szeredi.hu>
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References: <153313703562.13253.5766498657900728120.stgit@warthog.procyon.org.uk> <87d0uqpba5.fsf@xmission.com>
To:     "Eric W. Biederman" <ebiederm@xmission.com>
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> On Aug 10, 2018, at 7:05 AM, Eric W. Biederman <ebiederm@xmission.com> wro=
te:
>=20
>=20
> There is a serious problem with mount options today that fsopen does not
> address.  The problem is that mount options are ignored for block based
> filesystems, and any other type of filesystem that follows the same
> pattern.
>=20

> /dev/loop0 /root/loop0-noacl-noquota-nouser_xattr ext4 rw,relatime,nouser_=
xattr,noacl 0 0
> /dev/loop0 /root/loop0-acl-quota-user_xattr ext4 rw,relatime,nouser_xattr,=
noacl 0 0

To make sure I understand correctly: the problem is that the second mount ig=
nored the options because the device was already mounted, right?

For the new API, I think the only remotely sane approach is to refuse to mou=
nt or init or whatever you call it an already mounted bdev. If user code gen=
uinely needs to bind-mount an existing mount that is known only by its bdev,=
 we can add a specific API just for that.=