linux-kernel - Re: [patch 0/8] unprivileged mount syscall

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Mon, 16 Apr 2007 09:40:35 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	linuxram@...ibm.com, containers@...ts.osdl.org,
	linux-fsdevel@...r.kernel.org, akpm@...ux-foundation.org,
	util-linux-ng@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 0/8] unprivileged mount syscall

Miklos Szeredi <miklos@...redi.hu> writes:

>> Arn't there ways to escape chroot jails? Serge had pointed me to a URL
>> which showed chroots can be escaped. And if that is true than having all
>> user's private mount tree in the same namespace can be a security issue?
>
> No.  In fact chrooting the user into /share/$USER will actually
> _grant_ a privilege to the user, instead of taking it away.  It allows
> the user to modify it's root namespace, which it wouldn't be able to
> in the initial namespace.
>
> So even if the user could escape from the chroot (which I doubt), s/he
> would not be able to do any harm, since unprivileged mounting would be
> restricted to /share.  Also /share/$USER should only have read/search
> permission for $USER or no permissions at all, which would mean, that
> other users' namespaces would be safe from tampering as well.

A couple of points.
- chroot can be escaped, it is just a chdir for the root directory it
  is not a security feature.  The only security is that you have to be root to call chdir.
  A carefully done namespace setup won't have that issue.

- While it may not violate security as far as what a user is allowed to modify it may
  violate security as far as what a user is allowed to see.

There are interesting per login cases as well such as allowing a user to replicate
their mount tree from another machine when they log in.  When /home is on a network
filesystem this can be very practical and can allow propagation of mounts across
machines not just across a single login session.

Eric




-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/