> This also means that a kuid outside of the range 100000-165535
> is literally meaningless with respect to that mount - the kernel
> has no way to map it to an id valid in the filesystem.
> That is the real reason for the patch.
That is a compelling point. mounts inside a user-namespace are only
well-defined if every file's uid lies within the user-namespace.
I wish I had realised that prior to filing the bug report, and am
now happy to close it as not-a-bug (-: Thank you for your
highly informative replies.
** Changed in: linux (Ubuntu)
Status: Triaged => Invalid
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https://bugs.launchpad.net/bugs/1617388
Title:
When using overlayfs with kernel 4.4, some files cannot be deleted.
Status in linux package in Ubuntu:
Invalid
Bug description:
#!/bin/bash
# ---------------------------------------------------------------------
# This script exhibits a bug in overlayfs in kernel 4.4.
# The bug is not present in kernel 4.2.
# The bug can be reproduced in an x86_64 virtual-machine;
# 32-bit has not been tested.
#
# With kernel 4.2, the script output ends with:
# "script completed without encountering a kernel bug"
#
# With kernel 4.4, the script output ends with:
# "rm: cannot remove ‘mnt_ovl/sub/sub.txt’:
# Value too large for defined data type"
#
# The script depends upon lxc-usernsexec (part of the lxc1 package) to
# create a user-namespace.
#
# The script should be run as a normal user (not root), in a directory where
# the user has write-permission:
# ./script
# --------------------------------------------------------------------
cleanup()
{
[[ -d "$storedir" ]] || exit 1
cd "$storedir" || exit 1
[[ -d "$tmpdir" ]] || exit 1
lxc-usernsexec -m b:0:1000:1 -m b:100000:100000:1 -- rm -rf "$tmpdir"
}
trap cleanup EXIT
set -e
storedir="$(pwd)"
# create tmpdir
tmpdir="$(mktemp -d --tmpdir=.)"
cd "$tmpdir"
# create lowerdir for overlay
mkdir -p lower/sub
touch lower/lower.txt lower/sub/sub.txt
cd ..
chmod -R a+rwX "$tmpdir"
# run a script in a user namepace
lxc-usernsexec -m b:0:100000:65534 -- bash << EOF
set -e
cd "$tmpdir"
# create tmpfs
mkdir mnt_tmpfs
mount -t tmpfs tmpfs mnt_tmpfs
# create upperdir and workdir for overlay
mkdir mnt_tmpfs/{upper,work}
# mount overlay
mkdir mnt_ovl
mount -t overlay \
-o lowerdir=lower,upperdir=mnt_tmpfs/upper,workdir=mnt_tmpfs/work \
overlay mnt_ovl
echo 'overlay directory listing'
ls -RF mnt_ovl
echo ''
set -x
rm mnt_ovl/lower.txt # always succeeds
rm mnt_ovl/sub/sub.txt # fails with kernel 4.4+
set +x
echo 'script completed without encountering a kernel bug'
EOF
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