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Groups > linux.debian.bugs.dist > #1050689

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

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On Wed, Mar 03, 2021 at 11:30:20AM +0100, Nicolas Schier wrote:
> On Wed 03 Mar 2021 17:33:16 GMT Shengjing Zhu write:
> > 
> > On Wed, Mar 3, 2021 at 3:40 PM Nicolas Schier <nicolas@fjasle.eu> wrote:
> > > > [2]: https://lore.kernel.org/linux-unionfs/CAJfpegsiuf8ib5cvVrr=zHZ+Xu7BMMTT2eYapsEUdmPcRBUiwQ@mail.gmail.com/T/#t
> > >
> > > The overlay fs patchset [2] has been merged and with v5.10.13 (tested
> > > on linux-image-5.10.0-3-arm64) the issue is no more reproducible for
> > > me.  Might you want to re-check on your site?
> > >
> > 
> > If I understand correctly, the upstream patch is merged into the v5.11 tree.
> 
> Sorry.  Yes, you're right.
> 
> > And I still can reproduce the error on the Debian v5.10 kernel.
> 
> That confuses me quite a bit.  I did it once again on an ext4 mount 
> (still the 5.10.0-3-arm64 kernel):
> 
>   nsc@lillesand:/tmp$ cat /sys/module/overlay/parameters/permit_mounts_in_userns 
>   Y
>   nsc@lillesand:/tmp$ mkdir -p test/lower/a test/merged test/upper test/work
>   nsc@lillesand:/tmp$ uname -a | tee test/lower/a/a
>   Linux lillesand 5.10.0-3-arm64 #1 SMP Debian 5.10.13-1 (2021-02-06) aarch64 GNU/Linux
>   nsc@lillesand:/tmp$ unshare -m -U -r
>   root@lillesand:/tmp# mount -t overlay -o rw,lowerdir=/tmp/test/lower,upperdir=/tmp/test/upper,workdir=/tmp/test/work overlay /tmp/test/merged
>   root@lillesand:/tmp# rm -rf test/merged/a
>   root@lillesand:/tmp# find test -ls
>     1597776      4 drwxr-xr-x   6 root     root         4096 mars  3 08:24 test
>     1973978      4 drwxr-xr-x   2 root     root         4096 mars  3 08:27 test/upper
>     2099881      0 c---------   1 root     root       0,   0 mars  3 08:27 test/upper/a
>     1973978      4 drwxr-xr-x   1 root     root         4096 mars  3 08:27 test/merged
>     1714388      4 drwxr-xr-x   3 root     root         4096 mars  3 08:24 test/lower
>     1714389      4 drwxr-xr-x   2 root     root         4096 mars  3 08:27 test/lower/a
>     1714393      4 -rw-r--r--   1 root     root           86 mars  3 10:48 test/lower/a/a
>     1973979      4 drwxr-xr-x   3 root     root         4096 mars  3 10:48 test/work
>     2099880      4 d---------   2 root     root         4096 mars  3 10:48 test/work/work
>   root@lillesand:/tmp# 
> 
zsj@debian:~$ cat /sys/module/overlay/parameters/permit_mounts_in_userns 
Y
zsj@debian:~/t$ mkdir -p test/lower/a test/merged test/upper test/work
zsj@debian:~/t$ uname -a | tee test/lower/a/a
Linux debian 5.10.0-3-amd64 #1 SMP Debian 5.10.13-1 (2021-02-06) x86_64 GNU/Linux
zsj@debian:~/t$ unshare -m -U -r
root@debian:~/t# mount -t overlay -o rw,lowerdir=./test/lower,upperdir=./test/upper,workdir=./test/work overlay ./test/merged/
root@debian:~/t# rm -rf ./test/merged/a
rm: cannot remove './test/merged/a': Input/output error
root@debian:~/t# find test -ls
  7350352      4 drwxr-xr-x   6 root     root         4096 Mar  3 22:44 test
  7351341      4 drwxr-xr-x   3 root     root         4096 Mar  3 22:44 test/lower
  7353492      4 drwxr-xr-x   2 root     root         4096 Mar  3 22:44 test/lower/a
  7356441      4 -rw-r--r--   1 root     root           82 Mar  3 22:44 test/lower/a/a
  7356069      4 drwxr-xr-x   3 root     root         4096 Mar  3 22:45 test/work
  7358324      4 d---------   2 root     root         4096 Mar  3 22:45 test/work/work
  7358564      0 c---------   2 root     root       0,   0 Mar  3 22:45 test/work/work/#4
  7354400      4 drwxr-xr-x   3 root     root         4096 Mar  3 22:44 test/upper
  7358563      4 drwxr-xr-x   2 root     root         4096 Mar  3 22:45 test/upper/a
  7358564      0 c---------   2 root     root       0,   0 Mar  3 22:45 test/upper/a/a
  7354400      4 drwxr-xr-x   1 root     root         4096 Mar  3 22:44 test/merged
  7353492      4 drwxr-xr-x   1 root     root         4096 Mar  3 22:45 test/merged/a

> Do you see any kernel log message from overlay fs?  Might it depend on 
> the underlying filesystem? Can you create a white-out char dev node 
> manually?
> 

[1215353.859717] Setting dangerous option permit_mounts_in_userns - tainting kernel
[1215353.859841] overlayfs: overlayfs: Allowing overlay mounts in user namespaces bears security risks
[1215425.416543] overlayfs: upper fs does not support xattr, falling back to index=off and metacopy=off.

The underlying fs is ext4.

zsj@debian:~/t$ mount|grep nvme
/dev/nvme0n1p2 on / type ext4 (rw,relatime,errors=remount-ro)
/dev/nvme0n1p4 on /home type ext4 (rw,relatime)
/dev/nvme0n1p1 on /boot/efi type vfat (rw,relatime,fmask=0077,dmask=0077,codepage=437,iocharset=ascii,shortname=mixed,utf8,errors=remount-ro)

I don't know how to test "create a white-out char dev node manually".

Thanks

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Thread

Bug#969223: Can't rm directory on overlayfs in userns Nicolas Schier <nicolas@fjasle.eu> - 2021-03-03 08:50 +0100
  Bug#969223: Can't rm directory on overlayfs in userns Shengjing Zhu <zhsj@debian.org> - 2021-03-03 10:40 +0100
    Bug#969223: Can't rm directory on overlayfs in userns Nicolas Schier <nicolas@fjasle.eu> - 2021-03-03 11:40 +0100
      Bug#969223: Can't rm directory on overlayfs in userns Shengjing Zhu <zhsj@debian.org> - 2021-03-03 16:00 +0100
        Bug#969223: Can't rm directory on overlayfs in userns Nicolas Schier <nicolas@fjasle.eu> - 2021-03-11 07:20 +0100

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