SELinux Archive on
 help / color / Atom feed
From: Casey Schaufler <>
To: Paul Moore <>,,,
Cc:,,,, Stephen Smalley <>
Subject: Re: [RFC PATCH] security,anon_inodes,kvm: enable security support for anon inodes
Date: Thu, 20 Feb 2020 10:11:34 -0800
Message-ID: <> (raw)
In-Reply-To: <>

On 2/17/2020 4:14 PM, Paul Moore wrote:
> On Thu, Feb 13, 2020 at 2:41 PM Stephen Smalley <> wrote:
>> Add support for labeling and controlling access to files attached to anon
>> inodes. Introduce extended interfaces for creating such files to permit
>> passing a related file as an input to decide how to label the anon
>> inode. Define a security hook for initializing the anon inode security
>> attributes. Security attributes are either inherited from a related file
>> or determined based on some combination of the creating task and policy
>> (in the case of SELinux, using type_transition rules).  As an
>> example user of the inheritance support, convert kvm to use the new
>> interface for passing the related file so that the anon inode can inherit
>> the security attributes of /dev/kvm and provide consistent access control
>> for subsequent ioctl operations.  Other users of anon inodes, including
>> userfaultfd, will default to the transition-based mechanism instead.
>> Compared to the series in
>> this approach differs in that it does not require creation of a separate
>> anonymous inode for each file (instead storing the per-instance security
>> information in the file security blob), it applies labeling and control
>> to all users of anonymous inodes rather than requiring opt-in via a new
>> flag, it supports labeling based on a related inode if provided,
>> it relies on type transitions to compute the label of the anon inode
>> when there is no related inode, and it does not require introducing a new
>> security class for each user of anonymous inodes.
>> On the other hand, the approach in this patch does expose the name passed
>> by the creator of the anon inode to the policy (an indirect mapping could
>> be provided within SELinux if these names aren't considered to be stable),
>> requires the definition of type_transition rules to distinguish userfaultfd
>> inodes from proc inodes based on type since they share the same class,
>> doesn't support denying the creation of anonymous inodes (making the hook
>> added by this patch return something other than void is problematic due to
>> it being called after the file is already allocated and error handling in
>> the callers can't presently account for this scenario and end up calling
>> release methods multiple times), and may be more expensive
>> (security_transition_sid overhead on each anon inode allocation).
>> We are primarily posting this RFC patch now so that the two different
>> approaches can be concretely compared.  We anticipate a hybrid of the
>> two approaches being the likely outcome in the end.  In particular
>> if support for allocating a separate inode for each of these files
>> is acceptable, then we would favor storing the security information
>> in the inode security blob and using it instead of the file security
>> blob.
> Bringing this back up in hopes of attracting some attention from the
> fs-devel crowd and Al.  As Stephen already mentioned, from a SELinux
> perspective we would prefer to attach the security blob to the inode
> as opposed to the file struct; does anyone have any objections to
> that?

Sorry for the delay - been sick the past few days.

I agree that the inode is a better place than the file for information
about the inode. This is especially true for Smack, which uses
multiple extended attributes in some cases. I don't believe that any
except the access label will be relevant to anonymous inodes, but
I can imagine security modules with policies that would.

I am always an advocate of full xattr support. It goes a long
way in reducing the number and complexity of special case interfaces. 

  reply index

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-13 19:41 Stephen Smalley
2020-02-13 19:47 ` Stephen Smalley
2020-02-18  0:14 ` Paul Moore
2020-02-20 18:11   ` Casey Schaufler [this message]
2020-02-20 18:50     ` Daniel Colascione
2020-03-10 18:09       ` Daniel Colascione
2020-03-10 18:26         ` Stephen Smalley
2020-03-10 21:50           ` Daniel Colascione
2020-03-11 13:31             ` Stephen Smalley

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \ \ \ \ \ \ \ \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

SELinux Archive on

Archives are clonable:
	git clone --mirror selinux/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 selinux selinux/ \
	public-inbox-index selinux

Example config snippet for mirrors

Newsgroup available over NNTP:

AGPL code for this site: git clone