From: Christian Brauner <brauner@kernel.org>
To: Andy Lutomirski <luto@amacapital.net>
Cc: "Aleksa Sarai" <cyphar@cyphar.com>,
"Stas Sergeev" <stsp2@yandex.ru>,
"Serge E. Hallyn" <serge@hallyn.com>,
linux-kernel@vger.kernel.org,
"Stefan Metzmacher" <metze@samba.org>,
"Eric Biederman" <ebiederm@xmission.com>,
"Alexander Viro" <viro@zeniv.linux.org.uk>,
"Andy Lutomirski" <luto@kernel.org>, "Jan Kara" <jack@suse.cz>,
"Jeff Layton" <jlayton@kernel.org>,
"Chuck Lever" <chuck.lever@oracle.com>,
"Alexander Aring" <alex.aring@gmail.com>,
"David Laight" <David.Laight@aculab.com>,
linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org,
"Paolo Bonzini" <pbonzini@redhat.com>,
"Christian Göttsche" <cgzones@googlemail.com>
Subject: Re: [PATCH v5 0/3] implement OA2_CRED_INHERIT flag for openat2()
Date: Wed, 8 May 2024 09:32:10 +0200 [thread overview]
Message-ID: <20240508-flugverbindung-sonnig-dcfa4971152e@brauner> (raw)
In-Reply-To: <CALCETrWuVQ-ggnak40AX16PUnM43zhogceFN-3c_YAKZGvs5Og@mail.gmail.com>
On Tue, May 07, 2024 at 01:38:42PM -0700, Andy Lutomirski wrote:
> On Tue, May 7, 2024 at 12:42 AM Christian Brauner <brauner@kernel.org> wrote:
> >
> > > With my kernel hat on, maybe I agree. But with my *user* hat on, I
> > > think I pretty strongly disagree. Look, idmapis lousy for
> > > unprivileged use:
> > >
> > > $ install -m 0700 -d test_directory
> > > $ echo 'hi there' >test_directory/file
> > > $ podman run -it --rm
> > > --mount=type=bind,src=test_directory,dst=/tmp,idmap [debian-slim]
> >
> > $ podman run -it --rm --mount=type=bind,src=test_directory,dst=/tmp,idmap [debian-slim]
> >
> > as an unprivileged user doesn't use idmapped mounts at all. So I'm not
> > sure what this is showing. I suppose you're talking about idmaps in
> > general.
>
> Meh, fair enough. But I don't think this would have worked any better
> with privilege.
>
> Can idmaps be programmed by an otherwise unprivileged owner of a
> userns and a mountns inside?
Yes, but only for userns mountable filesystems that support idmapped
mounts. IOW, you need privilege over the superblock and the idmapping
you're trying to use.
>
> > Many idmappings to one is in principle possible and I've noted that idea
> > down as a possible extension at
> > https://github.com/uapi-group/kernel-features quite a while (2 years?) ago.
> >
> > > I haven't looked at the idmap implementation nearly enough to have any
> > > opinion as to whether squashing UID is practical or whether there's
> >
> > It's doable. The interesting bit to me was that if we want to allow
> > writes we'd need a way to determine what the uid/gid would be to write
> > down. Imho, that's not super difficult to solve though. The most obvious
> > one is that userspace can just determine it when creating the idmapped
> > mount.
>
> Seems reasonable to me. If this is set up by someone unprivileged, it
> would need to be that uid/gid.
next prev parent reply other threads:[~2024-05-08 7:32 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-26 13:33 [PATCH v5 0/3] implement OA2_CRED_INHERIT flag for openat2() Stas Sergeev
2024-04-26 13:33 ` [PATCH v5 1/3] fs: reorganize path_openat() Stas Sergeev
2024-04-26 13:33 ` [PATCH v5 2/3] open: add O_CRED_ALLOW flag Stas Sergeev
2024-04-27 2:12 ` kernel test robot
2024-04-26 13:33 ` [PATCH v5 3/3] openat2: add OA2_CRED_INHERIT flag Stas Sergeev
2024-04-28 16:41 ` [PATCH v5 0/3] implement OA2_CRED_INHERIT flag for openat2() Andy Lutomirski
2024-04-28 17:39 ` stsp
2024-04-28 19:15 ` stsp
2024-04-28 20:19 ` Andy Lutomirski
2024-04-28 21:14 ` stsp
2024-04-28 21:30 ` Andy Lutomirski
2024-04-28 22:12 ` stsp
2024-04-29 1:12 ` stsp
2024-04-29 9:12 ` Christian Brauner
2024-05-06 7:13 ` Aleksa Sarai
2024-05-06 17:29 ` Andy Lutomirski
2024-05-06 17:34 ` Andy Lutomirski
2024-05-06 19:34 ` David Laight
2024-05-06 21:53 ` Andy Lutomirski
2024-05-07 7:42 ` Christian Brauner
2024-05-07 20:38 ` Andy Lutomirski
2024-05-08 7:32 ` Christian Brauner [this message]
2024-05-08 17:30 ` Andy Lutomirski
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