From: Alejandro Colomar <alx@kernel.org>
To: Richard Weinberger <richard@nod.at>
Cc: "Serge E. Hallyn" <serge@hallyn.com>,
christian@brauner.io, ipedrosa@redhat.com, gscrivan@redhat.com,
"Andreas Grünbacher" <andreas.gruenbacher@gmail.com>,
acl-devel@nongnu.org, linux-man@vger.kernel.org,
linux-api@vger.kernel.org,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
ebiederm <ebiederm@xmission.com>
Subject: Re: [PATCH 0/3] Document impact of user namespaces and negative permissions
Date: Wed, 13 Sep 2023 16:35:18 +0200 [thread overview]
Message-ID: <0e7962b0-4d66-4d86-b245-a695dd421d01@kernel.org> (raw)
In-Reply-To: <1972367750.1870193.1693344767957.JavaMail.zimbra@nod.at>
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Hi Richard,
On 2023-08-29 23:32, Richard Weinberger wrote:
> ----- Ursprüngliche Mail -----
>> Von: "Alejandro Colomar" <alx@kernel.org>
>> Can you please provide a small shell session where this is exemplified?
>
> Sure. I sent the following to the shadow maintainers privately on Friday,
> but since the issue is already known for years I don't hesitate to share.
>
> # On a Debian Bookworm
> # So far no entries are installed.
> $ cat /etc/subuid
>
> # useradd automatically does so.
> $ useradd -m rw
> $ cat /etc/subuid
> rw:100000:65536
>
> # Let's create a folder where the group "nogames" has no permissions.
> $ mkdir /games
> $ echo win > /games/game.txt
> $ groupadd nogames
> $ chown -R root:nogames /games
> $ chmod 705 /games
>
> # User "rw" must not play games
> $ usermod -G nogames rw
>
> # Works as expected
> rw@localhost:~$ id
> uid=1000(rw) gid=1000(rw) groups=1000(rw),1001(nogames)
> rw@localhost:~$ cat /games/game.txt
> cat: /games/game.txt: Permission denied
>
> # By using unshare (which utilizes the newuidmap helper) we can get rid of the "nogames" group.
> rw@localhost:~$ unshare -S 0 -G 0 --map-users=100000,0,65536 --map-groups=100000,0,65536 id
> uid=0(root) gid=0(root) groups=0(root)
>
> rw@localhost:~$ unshare -S 0 -G 0 --map-users=100000,0,65536 --map-groups=100000,0,65536 cat /games/game.txt
> win
>
> Thanks,
> //richard
Thanks!
Please include this in the commit message (at least for the Linux man-pages
one).
Cheers,
Alex
--
<http://www.alejandro-colomar.es/>
GPG key fingerprint: A9348594CE31283A826FBDD8D57633D441E25BB5
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prev parent reply other threads:[~2023-09-13 14:35 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-08-29 20:58 [PATCH 0/3] Document impact of user namespaces and negative permissions Richard Weinberger
2023-08-29 20:58 ` [PATCH 1/3] man: Document pitfall with negative permissions and user namespaces Richard Weinberger
2023-08-30 8:19 ` Christian Brauner
2023-08-29 20:58 ` [PATCH 2/3] user_namespaces.7: " Richard Weinberger
2023-08-29 21:32 ` Alejandro Colomar
2023-08-29 21:38 ` Alejandro Colomar
2023-08-29 21:40 ` Richard Weinberger
2023-08-29 21:39 ` Richard Weinberger
2023-08-29 21:40 ` Alejandro Colomar
2023-08-30 9:26 ` Alejandro Colomar
2023-08-30 8:18 ` Christian Brauner
2023-08-29 20:58 ` [PATCH 3/3] man: " Richard Weinberger
2023-08-30 8:19 ` Christian Brauner
2023-08-29 21:26 ` [PATCH 0/3] Document impact of user namespaces and negative permissions Alejandro Colomar
2023-08-29 21:32 ` Richard Weinberger
2023-09-13 14:35 ` Alejandro Colomar [this message]
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