'ls -d /' not mediated with overlayfs and chroot

[Jamie Strandboge]

I'm not sure if this is a limitation of mediation or a bug, but performing an 'ls -d /' is allowed after creating an overlayfs on merged and chrooting to merged.

Reproducer:
$ tar -zxvf ./overlay-with-chroot-ls-root.tar.gz && sudo ./overlay-with-chroot-ls-root/drv
overlay-with-chroot-ls-root/
overlay-with-chroot-ls-root/p.in
overlay-with-chroot-ls-root/overlay.c
overlay-with-chroot-ls-root/drv
overlay-with-chroot-ls-root/tst
Created tmpdir '/tmp/tmp.ilA8cS947i'

Ubuntu 4.4.0-83.106-generic 4.4.70

Disabling kernel rate-limiting
kernel.printk_ratelimit = 0

Loading /tmp/tmp.ilA8cS947i/data/p

chdir(/tmp/tmp.ilA8cS947i/data/mnt)

Creating the overlay directories
- mkdir /tmp/tmp.ilA8cS947i/data/mnt/lower
- mkdir /tmp/tmp.ilA8cS947i/data/mnt/upper
- mkdir /tmp/tmp.ilA8cS947i/data/mnt/work
- mkdir /tmp/tmp.ilA8cS947i/data/mnt/merged

Populating /tmp/tmp.ilA8cS947i/data/mnt/lower
- /tmp/tmp.ilA8cS947i/data/mnt/lower/test-lower

Populating /tmp/tmp.ilA8cS947i/data/mnt/upper
- /tmp/tmp.ilA8cS947i/data/mnt/upper/test-upper

Perform the overlay
lower=/
upper=/tmp/tmp.ilA8cS947i/data/mnt/upper
work=/tmp/tmp.ilA8cS947i/data/mnt/work
where=/tmp/tmp.ilA8cS947i/data/mnt/merged
exe=/tmp/tmp.ilA8cS947i/data/tst
- mount('overlay', '/tmp/tmp.ilA8cS947i/data/mnt/merged', 'overlay', MS_MGC_VAL, lowerdir=/,upperdir=/tmp/tmp.ilA8cS947i/data/mnt/upper,workdir=/tmp/tmp.ilA8cS947i/data/mnt/work
 - success
- chdir('/tmp/tmp.ilA8cS947i/data/mnt/merged')
 - success
- chroot('.')
 - success
starting '/tmp/tmp.ilA8cS947i/data/tst'

ls -ld / (EXFAIL)
- ls -ld /
drwxr-xr-x 1 root root 4096 Jul 12 16:05 /
FAIL: could ls -ld /

- ls / (EXFAIL)
ls: cannot open directory '/': Permission denied

- ls -lR / (EXFAIL)
ls: cannot open directory '/': Permission denied

Cleaning up
- umount /tmp/tmp.ilA8cS947i/data/mnt/merged
- rm -rf /tmp/tmp.ilA8cS947i

Tested on 4.4, 4.10 and 4.11. Not sure if this is a duplicate or related to bug #1703988.