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

[Paul Moore]

On Wed, Jul 13, 2016 at 10:44 AM, Vivek Goyal <vgoyal@xxxxxxxxxx> 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.

Miklos, this patchset depends on patches in your overlayfs-next
branch, I assume you're pushing that branch during the upcoming merge
window?

James, assuming the overlayfs-next branch is pulled during the merge
window, can you rebase your linux-security#next branch to v4.8-rc1
once Linus tags it?

-- 
paul moore
www.paul-moore.com