Bug#896908: busybox cpio: fails to extract absolute symlinks

[Tzafrir Cohen <tzafrir@debian.org>]

Package: busybox-static
Version: 1:1.27.2-2
Severity: normal

I tried building debirf on a current Sid system (chroot, rather). The
generated initramfs failed to properly boot. I noticed that the
second-stage rootfs in it, is OK but when extracted misses /sbin/init
and a number of other symlinks from /sbin and thus the system fails to
boot due to a missing init.

cpio on Stretch and on Sid as well as busybox cpio on Stretch
(1:1.22.0-19+b3) extract the absolute symlinks OK, but busybox cpio on
Sid does not extract absolute symlinks.

A test for the problem:

#!/bin/sh
#cpio="cpio"
cpio="/bin/busybox cpio"

mkdir -p test_dir
cd test_dir

rm -rf src_dir
mkdir src_dir
cd src_dir
ln -s /bin/true absolute_link
touch a_file
ln -s a_file relative_link
# Create with the regular cpio:
ls absolute_link a_file relative_link | cpio -H newc -o >../test.cpio
cd ..

rm -rf dst_dir
mkdir dst_dir
cd dst_dir
# Extract with the tested cpio:
$cpio -H newc -i <../test.cpio
count=`ls | wc -l`
if [ "$count" = 2 ]; then
	echo "absolute links were not extracted"
fi



-- System Information:
Debian Release: 9.4
  APT prefers stable-updates
  APT policy: (500, 'stable-updates'), (500, 'stable')
Architecture: amd64 (x86_64)
Foreign Architectures: armhf

Kernel: Linux 4.9.0-6-amd64 (SMP w/4 CPU cores)
Locale: LANG=he_IL.UTF-8, LC_CTYPE=he_IL.UTF-8 (charmap=UTF-8), LANGUAGE=he_IL.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)