Comment 0 for bug 1665921

Step to reproduse:

    - Crete dircetory with other directories and files.
    - Chown some files in this directory, set any non-root permissions.
    - Export nfs share with 'ro' permissions.
    - Mount nfs share.
    - Mount ovrelayfs with nfs as lowerdir
    - Try to read theese non-root files or directories:

Example for overlay mount:

    # ls -l /var/lib/libvirt
    total 16
    drwx--x--x 2 root root 4096 Oct 10 07:33 boot
    drwx--x--x 2 root root 4096 Oct 10 07:33 images
    drwxr-x--- 3 libvirt-qemu kvm 4096 Jan 11 21:49 qemu
    drwx------ 2 root root 4096 Oct 10 07:33 sanlock

    # ls -l /var/lib/libvirt/qemu/
    ls: cannot open directory '/var/lib/libvirt/qemu/': Operation not supported

And for nfs mount:

    # ls -l /rofs/var/lib/libvirt
    total 16
    drwx--x--x 2 root root 4096 Oct 10 07:33 boot
    drwx--x--x 2 root root 4096 Oct 10 07:33 images
    drwxr-x--- 3 libvirt-qemu kvm 4096 Jan 11 21:49 qemu
    drwx------ 2 root root 4096 Oct 10 07:33 sanlock

    # ls -l /rofs/var/lib/libvirt/qemu/
    total 4
    drwxr-xr-x 3 root root 4096 Jan 11 21:49 channel

If I reset permission, it helps:

    # chown libvirt-qemu:kvm /var/lib/libvirt/qemu
    # ls -l /var/lib/libvirt/qemu/
    total 4
    drwxr-xr-x 3 root root 4096 Jan 11 21:49 channel

My mounts (from /proc/mounts)

    192.168.101.61:/data/opt/ltsp/amd64 /rofs nfs ro,relatime,vers=3,rsize=1048576,wsize=1048576,namlen=255,hard,nolock,proto=tcp,port=2049,timeo=7,retrans=10,sec=sys,local_lock=all,addr=192.168.101.61 0 0
    overlay / overlay rw,relatime,lowerdir=/rofs,upperdir=/cow/up,workdir=/cow/work 0 0

I tested it nfs3 and nfs4 mount, with this kenels:

    # uname -a
    Linux controller03 4.4.0-62-generic #83-Ubuntu SMP Wed Jan 18 14:10:15 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux

    # uname -a
    Linux m1c18n1 4.8.0-36-generic #36~16.04.1-Ubuntu SMP Sun Feb 5 09:39:57 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux