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[Launchpad Bug Tracker <1555997@xxxxxxxxxxxxxxxxxx>]

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I'm investigating some failures in autopkgtest's testsuite, and stumbled
over something really weird: In an ephemeral container it is apparently
not possible any more to chmod files that started out being root owned
and got chowned later:

$ sudo lxc-start-ephemeral -o adt-wily
(log in as ubuntu/ubuntu)
ubuntu@adt-wily-hvzj1eoa:~$ echo hello | sudo tee /tmp/testfile
[sudo] password for ubuntu:
hello
ubuntu@adt-wily-hvzj1eoa:~$ sudo chown ubuntu:ubuntu /tmp/testfile
ubuntu@adt-wily-hvzj1eoa:~$ chmod +x /tmp/testfile
chmod: changing permissions of ‘/tmp/testfile’: Operation not permitted

However, if the file was *not* previously chowned, it works as expected:

ubuntu@adt-wily-hvzj1eoa:~$ echo hello > /tmp/testfile2
ubuntu@adt-wily-hvzj1eoa:~$ chmod +x /tmp/testfile2
ubuntu@adt-wily-hvzj1eoa:~$ chmod -x /tmp/testfile2

(no errors and testfile2 becomes executable)

There is no visible permission difference in the files at all, other
than being group-writable (but changing the group w bit in either
direction does not change the error at all):

-rw-r--r-- 1 ubuntu ubuntu 6 Mar 11 10:26 /tmp/testfile
-rw-rw-r-- 1 ubuntu ubuntu 6 Mar 11 10:26 /tmp/testfile2

ubuntu@adt-wily-hvzj1eoa:~$ stat /tmp/testfile*
  File: ‘/tmp/testfile’
  Size: 6         	Blocks: 8          IO Block: 4096   regular file
Device: 15h/21d	Inode: 28          Links: 1
Access: (0644/-rw-r--r--)  Uid: ( 1000/  ubuntu)   Gid: ( 1000/  ubuntu)
Access: 2016-03-11 10:26:19.574364117 +0100
Modify: 2016-03-11 10:26:19.574364117 +0100
Change: 2016-03-11 10:26:21.930343210 +0100
 Birth: -
  File: ‘/tmp/testfile2’
  Size: 6         	Blocks: 8          IO Block: 4096   regular file
Device: 15h/21d	Inode: 29          Links: 1
Access: (0664/-rw-rw-r--)  Uid: ( 1000/  ubuntu)   Gid: ( 1000/  ubuntu)
Access: 2016-03-11 10:26:58.730145919 +0100
Modify: 2016-03-11 10:26:58.730145919 +0100
Change: 2016-03-11 10:27:44.530203985 +0100
 Birth: -

There are also no ACLs involved (I checked with getfacl).

This does not happen with a normal lxc-start, so this might very well be
a bug in Linux' overlayfs. However, it also does not happen with the
more modern "sudo lxc-copy -n adt-wily --ephemeral --foreground" -- bug
perhaps this isn't using overlayfs?

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: lxc 2.0.0~rc9-0ubuntu1
ProcVersionSignature: Ubuntu 4.4.0-11.26-generic 4.4.4
Uname: Linux 4.4.0-11-generic x86_64
ApportVersion: 2.20-0ubuntu3
Architecture: amd64
CurrentDesktop: i3
Date: Fri Mar 11 10:21:20 2016
EcryptfsInUse: Yes
PackageArchitecture: all
SourcePackage: lxc
UpgradeStatus: No upgrade log present (probably fresh install)
defaults.conf:
 lxc.network.type = veth
 lxc.network.link = lxcbr0
 lxc.network.flags = up
 lxc.network.hwaddr = 00:16:3e:xx:xx:xx
dnsmasq.conf:
 enable-tftp
 tftp-root=/tmp/tftp
 dhcp-boot=pxelinux.0
lxc.conf: lxc.lxcpath = /srv/lxc

** Affects: linux (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: amd64 apport-bug xenial
-- 
overlay fs regression: chmod fails with "Operation not permitted" on chowned files
https://bugs.launchpad.net/bugs/1555997
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