Re: [PATCH] btrfs: Make btrfs handle security mount options internally to avoid losing security label.

[Eryu Guan <guaneryu@gmail.com>]

On Mon, Oct 06, 2014 at 09:29:25AM -0400, Josef Bacik wrote:
> On 09/23/2014 01:40 AM, Qu Wenruo wrote:
> >[BUG]
> >Originally when mount btrfs with "-o subvol=" mount option, btrfs will
> >lose all security lable.
> >And if the btrfs fs is mounted somewhere else, due to the lost of
> >security lable, SELinux will refuse to mount since the same super block
> >is being mounted using different security lable.
> >
> >[REPRODUCER]
> >With SELinux enabled:
> >  #mkfs -t btrfs /dev/sda5
> >  #mount -o context=system_u:object_r:nfs_t:s0 /dev/sda5 /mnt/btrfs
> >  #btrfs subvolume create /mnt/btrfs/subvol
> >  #mount -o subvol=subvol,context=system_u:object_r:nfs_t:s0 /dev/sda5
> >   /mnt/test
> >
> >kernel message:
> >SELinux: mount invalid.  Same superblock, different security settings
> >for (dev sda5, type btrfs)
> >
> >[REASON]
> >This happens because btrfs will call vfs_kern_mount() and then
> >mount_subtree() to handle subvolume name lookup.
> >First mount will cut off all the security lables and when it comes to
> >the second vfs_kern_mount(), it has no security label now.
> >
> >[FIX]
> >This patch will makes btrfs behavior much more like nfs,
> >which has the type flag FS_BINARY_MOUNTDATA,
> >making btrfs handles the security label internally.
> >So security label will be set in the real mount time and won't lose
> >label when use with "subvol=" mount option.
> >
> 
> Please make this an xfstest, I'm going to change how subvols are mounted in
> a bit and I'd like to make sure I don't break anything.  Thanks,

Hi Qu, I'll submit one xfstest, just want to make sure you don't do
duplicated work here.

Thanks,
Eryu