Bug#969223: Can't rm directory on overlayfs in userns

[Shengjing Zhu <zhsj@debian.org>]

Source: linux
Version: 5.7.10-1
Severity: normal

Hi,

After enabling overlayfs for userns, I find it doesn't work as expected.

$ cat /sys/module/overlay/parameters/permit_mounts_in_userns 
Y

zsj@debian:~/test$ pwd
/home/zsj/test
zsj@debian:~/test$ tree
.
├── lower
│   └── a
│       └── a
├── merged
├── upper
└── work

zsj@debian:~/test$ unshare -m -U -r
root@debian:~/test# mount -t overlay -o rw,lowerdir=/home/zsj/test/lower,upperdir=/home/zsj/test/upper,workdir=/home/zsj/test/work overlay /home/zsj/test/merged
root@debian:~/test# rm -rf merged/a
rm: cannot remove 'merged/a': Input/output error

-- System Information:
Debian Release: bullseye/sid
  APT prefers testing
  APT policy: (500, 'testing')
Architecture: amd64 (x86_64)

Kernel: Linux 5.7.0-2-amd64 (SMP w/4 CPU threads)
Kernel taint flags: TAINT_USER, TAINT_FIRMWARE_WORKAROUND
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), LANGUAGE not set
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)