Bug#869771: grub-pc-bin: can not load 4.9.30-2+deb9u2 kernel on a compressed squashfs

[Juha Erkkilä]

Package: grub-pc-bin
Version: 2.02~beta3-5
Severity: normal

Dear Maintainer,

grub can not load the latest linux-image on Debian Stretch, that is currently
package name linux-image-4.9.0-3-amd64, version 4.9.30-2+deb9u2, when this
image is inside a compressed squashfs-image.  The problem was already present with
the previous linux-image, which can be found here:

  http://snapshot.debian.org/archive/debian/20170609T034604Z/pool/main/l/linux/linux-image-4.9.0-3-amd64_4.9.30-1_amd64.deb

To reproduce, create a squashfs-image with only the vmlinuz-image inside it:

  sudo apt-get install squashfs-tools
  mkdir -p squashfs_testdir
  cp -p /boot/vmlinuz-4.9.0-3-amd64 squashfs_testdir/
  rm -f squashfs_testimage.img
  mksquashfs squashfs_testdir squashfs_testimage.img

Then copy this test-image to some place where it can be easily accessed by
grub, in my case it is in "(lvm/puavo-images)/squashfs_testimage.img".
Boot grub and trigger the command prompt mode with "c", then type:

  grub> loopback loop (lvm/puavo-images)/squashfs_testimage.img
  grub> crc (loop)/vmlinuz-4.9.0-3-amd64
  error: unsupported gzip format
  grub> linux (loop)/vmlinuz-4.9.0-3-amd64
  error: unsupported gzip format

If the image is compressed with algorithm other than "gzip",
the error message might contain "incorrect compressed chunk".

This problem occurs because the "vmlinuz-4.9.0-3-amd64" file ends up
into squashfs-image with zero-sized blocks, which the current grub
implementation does not know how to handle when the image is compressed.
Apparently this is an optimization with sparse files.

This problem has been fixed in the grub-version that is in currently
in testing, version 2.02-2.  I believe the relevant commit is this:
https://git.launchpad.net/grub/commit/?id=951306c5094d2bfb46d5baedfde84a2015c4a3fa

However, because this issue occurs with the latest default kernel in
Stretch, I feel the issue is serious enough to warrant a bug report.

Juha

-- System Information:
Debian Release: 9.1
  APT prefers stable
  APT policy: (990, 'stable'), (500, 'oldstable-updates'), (500, 'oldoldstable-updates'), (500, 'oldoldstable'), (500, 'oldstable'), (30, 'xenial-updates'), (30, 'xenial-security'), (30, 'xenial'), (1, 'experimental')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 4.9.0-2-amd64 (SMP w/4 CPU cores)
Locale: LANG=fi_FI.UTF-8, LC_CTYPE=fi_FI.UTF-8 (charmap=UTF-8), LANGUAGE=fi (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages grub-pc-bin depends on:
ii  grub-common         2.02~beta3-5
ii  libc6               2.24-11+deb9u1
ii  libdevmapper1.02.1  2:1.02.137-2

grub-pc-bin recommends no packages.

Versions of packages grub-pc-bin suggests:
ii  desktop-base  9.0.2

-- no debconf information