linux-kernel - Re: [RFC PATCH 0/9][V3] Overlayfs SELinux Support

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Date:	Wed, 10 Aug 2016 11:11:12 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	Paul Moore <paul@...l-moore.com>
Cc:	Vivek Goyal <vgoyal@...hat.com>,
	Stephen Smalley <sds@...ho.nsa.gov>,
	Dan Walsh <dwalsh@...hat.com>, Paul Moore <pmoore@...hat.com>,
	James Morris <jmorris@...ei.org>,
	Casey Schaufler <casey@...aufler-ca.com>,
	linux-kernel@...r.kernel.org,
	"linux-unionfs@...r.kernel.org" <linux-unionfs@...r.kernel.org>,
	LSM <linux-security-module@...r.kernel.org>,
	David Howells <dhowells@...hat.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org
Subject: Re: [RFC PATCH 0/9][V3] Overlayfs SELinux Support

On Tue, Aug 9, 2016 at 3:19 AM, Paul Moore <paul@...l-moore.com> wrote:
> On Thu, Jul 21, 2016 at 5:16 PM, Paul Moore <paul@...l-moore.com> wrote:
>> On Wed, Jul 13, 2016 at 10:44 AM, Vivek Goyal <vgoyal@...hat.com> wrote:
>>> Hi All,
>>>
>>> Please find attached the V3 of patches. Changes since V2 are as follows.
>>>
>>> - Fixed the build issue with CONFIG_SECURITY=n.
>>>
>>> - Dan Walsh was writing more tests for selinux-testsuite and noted couple
>>>   of issues. I have fixed those issues and added two more patches in series.
>>>
>>>   1. We are resetting MAY_WRITE check for lower inode assuming file will
>>>      be coiped up. But this is not true for special_file() as these files
>>>      are not copied up. So checks should not be reset in case of special
>>>      file.
>>>
>>>   2. We are resetting MAY_WRITE check for lower inode assuming file will
>>>      be copied up. But this also should mean that mounter has permission
>>>      to MAY_READ lower file for copy up to succeed. So add MAY_READ
>>>      check while resetting MAY_WRITE.
>>>
>>> Original description of patches follows.
>>>
>>> Following are RFC patches to support SELinux with overlayfs. I started
>>> with David Howells's latest posting on this topic and started modifying
>>> patches. These patches apply on top of overlayfs-next branch of miklos
>>> vfs git tree.
>>>
>>> git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs.git overlayfs-next
>>>
>>> These patches can be pulled from my branch too.
>>>
>>> https://github.com/rhvgoyal/linux/commits/overlayfs-selinux-mounter-next
>>>
>>> Thanks to Dan Walsh, Stephen Smalley and Miklos Szeredi for numerous
>>> conversation and ideas in helping figuring out what one reasonable
>>> implementation might look like.
>>>
>>> Dan Walsh has been writing tests for selinux overlayfs in selinux-testsuite.
>>> These patches pass those tests now
>>>
>>> https://github.com/rhatdan/selinux-testsuite/commits/master
>>>
>>> Posting these patches for review and comments.
>>>
>>> These patches introduce 3 new security hooks.
>>>
>>> - security_inode_copy_up(), is called when a file is copied up. This hook
>>>   prepares a new set of cred which is used for copy up operation. And
>>>   new set of creds are prepared so that ->create_sid can be set appropriately
>>>   and newly created file is labeled properly.
>>>
>>>   When a file is copied up, label of lower file is retained except for the
>>>   case of context= mount where new file gets the label from context= option.
>>>
>>> - security_inode_copy_up_xattr(), is called when xattrs of a file are
>>>   being copied up. Before this we already called security_inode_copy_up()
>>>   and created new file and copied up data. That means file already got
>>>   labeled properly and there is no need to take SELINUX xattr of lower
>>>   file and overwrite the upper file xattr. So this hook is used to avoid
>>>   copying up of SELINUX xattr.
>>>
>>> - dentry_create_files_as(), is called when a new file is about to be created.
>>>   This hook determines what the label of the file should be if task had
>>>   created that file in upper/ and sets create_sid accordingly in the passed
>>>   in creds.
>>>
>>>   Normal transition rules don't work for the case of context mounts as
>>>   underlying file system is not aware of context option which only overlay
>>>   layer is aware of. For non-context mounts, creation can happen in work/
>>>   dir first and then file might be renamed into upper/, and it might get
>>>   label based on work/ dir. So this hooks helps avoiding all these issues.
>>>
>>>   When a new file is created in upper/, it gets its label based on transition
>>>   rules. For the case of context mount, it gets the label from context=
>>>   option.
>>>
>>> Any feedback is welcome.
>>
>> Hi Vivek,
>>
>> These patches look fine to me, thanks for all your hard work and to
>> everyone who helped review and provide feedback.  I have tagged these
>> patches for merging into the SELinux next branch after this merge
>> window.
>
> Okay, I just merged these patches into selinux#next.  With the
> exception of some changes to restore the mode argument to
> ovl_create_or_link() and to fix some whitespace damage the patches
> were merged cleanly.

Don't need to add the back the mode argument, just use stat->mode.

Thanks,
Miklos