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SubjectRe: [PATCH] cgroups: devices: add Documentation/ file
Quoting Randy Dunlap (randy.dunlap@oracle.com):
> On Thu, 27 Mar 2008 10:12:27 -0500 Serge E. Hallyn wrote:
>
> > Fill a Documentation/controllers/devices.txt file with a
> > modified text from the patch description.
> >
> > Signed-off-by: Serge E. Hallyn <serue@us.ibm.com>
> > ---
> > Documentation/controllers/devices.txt | 48 +++++++++++++++++++++++++++++++++
> > 1 files changed, 48 insertions(+), 0 deletions(-)
> > create mode 100644 Documentation/controllers/devices.txt
> >
> > diff --git a/Documentation/controllers/devices.txt b/Documentation/controllers/devices.txt
> > new file mode 100644
> > index 0000000..a157f53
> > --- /dev/null
> > +++ b/Documentation/controllers/devices.txt
> > @@ -0,0 +1,48 @@
> > +Device Whitelist Controller
> > +
> > +1. Description:
> > +
>
> ...
>
> > +The root device cgroup starts with rwm to 'all'. A child devices
>
> device's

That's actually not right, but 'child device cgroup' does sound better.

>
> > +cgroup gets a copy of the parent. Administrators can then remove
> > +devices from the whitelist or add new entries. A child cgroup can
> > +never receive a device access which is denied its parent. However
> > +when a device access is removed from a parent it will not also be
> > +removed from the child(ren).
> > +
> > +2. User Interface
> > +
> ...
> > +
> > +3. Security
> > +
> > +Any task can move itself between cgroups. This of clearly won't
>
> s/of//

Yup, oops.

New patch attached. Thanks, Randy.

-serge

> > +suffice, but we can decide the best way to adequately restrict
> > +movement as people get some experience with this. We may just want
> > +to require CAP_SYS_ADMIN, which at least is a separate bit from
> > +CAP_MKNOD. We may want to just refuse moving to a cgroup which
> > +isn't a descendent of the current one. Or we may want to use
> > +CAP_MAC_ADMIN, since we really are trying to lock down root.
> > +
> > +CAP_SYS_ADMIN is needed to modify the whitelist or move another
> > +task to a new cgroup. (Again we'll probably want to change that).
> > +
> > +A cgroup may not be granted more permissions than the cgroup's
> > +parent has.
> > --
>
> ---
> ~Randy


From c5a7bd6599ebe47b8711ba66b1c41a81935a12af Mon Sep 17 00:00:00 2001
From: Serge E. Hallyn <serue@us.ibm.com>
Date: Thu, 27 Mar 2008 08:11:10 -0700
Subject: [PATCH 1/1] cgroups: devices: add Documentation/ file

Fill a Documentation/controllers/devices.txt file with a
modified text from the patch description.

Signed-off-by: Serge E. Hallyn <serue@us.ibm.com>
---
Documentation/controllers/devices.txt | 48 +++++++++++++++++++++++++++++++++
1 files changed, 48 insertions(+), 0 deletions(-)
create mode 100644 Documentation/controllers/devices.txt
diff --git a/Documentation/controllers/devices.txt b/Documentation/controllers/devices.txt
new file mode 100644
index 0000000..a157f53
--- /dev/null
+++ b/Documentation/controllers/devices.txt
@@ -0,0 +1,48 @@
+Device Whitelist Controller
+
+1. Description:
+
+Implement a cgroup to track and enforce open and mknod restrictions
+on device files. A device cgroup associates a device access
+whitelist with each cgroup. A whitelist entry has 4 fields.
+'type' is a (all), c (char), or b (block). 'all' means it applies
+to all types and all major and minor numbers. Major and minor are
+either an integer or * for all. Access is a composition of r
+(read), w (write), and m (mknod).
+
+The root device cgroup starts with rwm to 'all'. A child device
+cgroup gets a copy of the parent. Administrators can then remove
+devices from the whitelist or add new entries. A child cgroup can
+never receive a device access which is denied its parent. However
+when a device access is removed from a parent it will not also be
+removed from the child(ren).
+
+2. User Interface
+
+An entry is added using devices.allow, and removed using
+devices.deny. For instance
+
+ echo 'c 1:3 mr' > /cgroups/1/devices.allow
+
+allows cgroup 1 to read and mknod the device usually known as
+/dev/null. Doing
+
+ echo a > /cgroups/1/devices.deny
+
+will remove the default 'a *:* mrw' entry.
+
+3. Security
+
+Any task can move itself between cgroups. This clearly won't
+suffice, but we can decide the best way to adequately restrict
+movement as people get some experience with this. We may just want
+to require CAP_SYS_ADMIN, which at least is a separate bit from
+CAP_MKNOD. We may want to just refuse moving to a cgroup which
+isn't a descendent of the current one. Or we may want to use
+CAP_MAC_ADMIN, since we really are trying to lock down root.
+
+CAP_SYS_ADMIN is needed to modify the whitelist or move another
+task to a new cgroup. (Again we'll probably want to change that).
+
+A cgroup may not be granted more permissions than the cgroup's
+parent has.
--
1.5.1


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