[Bug 1753572] [NEW] cpio in Busybox 1.27 ingnores "unsafe links"

[Bryan Seitz]

Public bug reported:

Description:    Ubuntu Bionic Beaver (development branch)
Release:        18.04

busybox:
  Installed: 1:1.27.2-2ubuntu3
  Candidate: 1:1.27.2-2ubuntu3

3) Expected my CPIO archive to be fully extracted with proper symlinks
Command: unxz < /rootfs.cxz | cpio -i

4) 'Unsafe' symlinks were ignored such as:

sbin/init -> /lib/systemd/systemd

With the broken 1.27 sbin/init does not get created at all and my debirf
initrd fails to load/boot properly.

1.22 from Xenial works.
GNU Cpio also works.

It looks like 1.28 adds an env var to override this behavior:

libarchive: do not extract unsafe symlinks unless
$EXTRACT_UNSAFE_SYMLINKS=1

** Affects: busybox (Ubuntu)
     Importance: Undecided
         Status: Confirmed


** Tags: busybox cpio

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https://bugs.launchpad.net/bugs/1753572

Title:
  cpio in Busybox 1.27 ingnores "unsafe links"

Status in busybox package in Ubuntu:
  Confirmed

Bug description:
  Description:    Ubuntu Bionic Beaver (development branch)
  Release:        18.04

  busybox:
    Installed: 1:1.27.2-2ubuntu3
    Candidate: 1:1.27.2-2ubuntu3

  3) Expected my CPIO archive to be fully extracted with proper symlinks
  Command: unxz < /rootfs.cxz | cpio -i

  4) 'Unsafe' symlinks were ignored such as:

  sbin/init -> /lib/systemd/systemd

  With the broken 1.27 sbin/init does not get created at all and my
  debirf initrd fails to load/boot properly.

  1.22 from Xenial works.
  GNU Cpio also works.

  It looks like 1.28 adds an env var to override this behavior:

  libarchive: do not extract unsafe symlinks unless
  $EXTRACT_UNSAFE_SYMLINKS=1

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