linux-kernel - Re: overlayfs: caller_credentials option bypass creator

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, 18 Jun 2018 14:59:50 -0700
From:   Mark Salyzyn <salyzyn@...roid.com>
To:     Vivek Goyal <vgoyal@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Miklos Szeredi <miklos@...redi.hu>,
        Jonathan Corbet <corbet@....net>,
        linux-unionfs@...r.kernel.org, linux-doc@...r.kernel.org,
        Daniel Walsh <dwalsh@...hat.com>,
        Stephen Smalley <sds@...ho.nsa.gov>
Subject: Re: overlayfs: caller_credentials option bypass creator_cred

On 06/18/2018 12:43 PM, Vivek Goyal wrote:
> Will it be acceptable to write security policies in such a way so that
> mounter has access as well.
Unfortunately No. Policy of minimizing attack surface for a contained 
root service (init in this case). Just because it can mount, does not 
mean it can modify critical content; an attacker could use this to open 
a hole.

> Current model does assume that mounter has privileges on underlying files.

Only ones it appears to need is the workdir AFAIK, had to add ability to 
create in the <wordir> xattr in order to enable r/w mounts later. 
Although not all corners were tested, I did not see any copy_up issues 
b/c the caller had the privs in the Android security model when mounted 
with this new flag.

-- Mark