Re: [PATCH v19 0/4] overlayfs override_creds=off & nested get xattr fix

From: Paul Moore <paul@paul-moore.com>
To: Vivek Goyal <vgoyal@redhat.com>
Cc: Amir Goldstein <amir73il@gmail.com>,
	David Anderson <dvander@google.com>,
	Mark Salyzyn <salyzyn@android.com>,
	Miklos Szeredi <miklos@szeredi.hu>,
	Jonathan Corbet <corbet@lwn.net>,
	"Eric W . Biederman" <ebiederm@xmission.com>,
	Randy Dunlap <rdunlap@infradead.org>,
	Stephen Smalley <sds@tycho.nsa.gov>,
	John Stultz <john.stultz@linaro.org>,
	linux-doc@vger.kernel.org,
	linux-kernel <linux-kernel@vger.kernel.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	overlayfs <linux-unionfs@vger.kernel.org>,
	LSM List <linux-security-module@vger.kernel.org>,
	kernel-team <kernel-team@android.com>,
	selinux@vger.kernel.org, paulmoore@microsoft.com,
	Luca.Boccassi@microsoft.com
Subject: Re: [PATCH v19 0/4] overlayfs override_creds=off & nested get xattr fix
Date: Fri, 3 Dec 2021 11:04:23 -0500	[thread overview]
Message-ID: <CAHC9VhQ8NJdCKE7x5qzWoSDZvboyyy+fmOkA-cTN0XrvfYepeA@mail.gmail.com> (raw)
In-Reply-To: <Yao51m9EXszPsxNN@redhat.com>

On Fri, Dec 3, 2021 at 10:38 AM Vivek Goyal <vgoyal@redhat.com> wrote:
> On Wed, Nov 17, 2021 at 09:36:42AM +0200, Amir Goldstein wrote:
> > On Wed, Nov 17, 2021 at 3:58 AM David Anderson <dvander@google.com> wrote:
> > >
> > > Mark Salyzyn (3):
> > >   Add flags option to get xattr method paired to __vfs_getxattr
> > >   overlayfs: handle XATTR_NOSECURITY flag for get xattr method
> > >   overlayfs: override_creds=off option bypass creator_cred
> > >
> > > Mark Salyzyn + John Stultz (1):
> > >   overlayfs: inode_owner_or_capable called during execv
> > >
> > > The first three patches address fundamental security issues that should
> > > be solved regardless of the override_creds=off feature.
> > >
> > > The fourth adds the feature depends on these other fixes.
> > >
> > > By default, all access to the upper, lower and work directories is the
> > > recorded mounter's MAC and DAC credentials.  The incoming accesses are
> > > checked against the caller's credentials.
> > >
> > > If the principles of least privilege are applied for sepolicy, the
> > > mounter's credentials might not overlap the credentials of the caller's
> > > when accessing the overlayfs filesystem.  For example, a file that a
> > > lower DAC privileged caller can execute, is MAC denied to the
> > > generally higher DAC privileged mounter, to prevent an attack vector.
> > >
> > > We add the option to turn off override_creds in the mount options; all
> > > subsequent operations after mount on the filesystem will be only the
> > > caller's credentials.  The module boolean parameter and mount option
> > > override_creds is also added as a presence check for this "feature",
> > > existence of /sys/module/overlay/parameters/overlay_creds
>
> BTW, where is patch 1 of the series. I can't seem to find it.

Lore to the rescue ...

https://lore.kernel.org/selinux/20211117015806.2192263-2-dvander@google.com/

-- 
paul moore
www.paul-moore.com