feat: enable CONFIG_SQUASHFS=m for kernel-6.12 and kernel-6.18

[ginglis13]

Issue number:

Closes bottlerocket-os/bottlerocket#4845

Description of changes:

Enable the squashfs kernel module so that userspace applications
can mount squashfs filesystems. This restores the squashfs support
that was present in kernel-6.1 but dropped in newer kernels.

Configs are copied as the kernel-6.1 configs for squashfs:

bottlerocket-kernel-kit/packages/kernel-6.1/config-bottlerocket

Lines 14 to 29 in e9e21d2

	# Support for squashfs used to provide kernel headers with zstd compression
	CONFIG_SQUASHFS=m
	CONFIG_SQUASHFS_FILE_CACHE=y
	# CONFIG_SQUASHFS_FILE_DIRECT is not set
	CONFIG_SQUASHFS_DECOMP_SINGLE=y
	# CONFIG_SQUASHFS_DECOMP_MULTI is not set
	# CONFIG_SQUASHFS_DECOMP_MULTI_PERCPU is not set
	CONFIG_SQUASHFS_XATTR=y
	CONFIG_SQUASHFS_ZLIB=y
	CONFIG_SQUASHFS_LZ4=y
	CONFIG_SQUASHFS_LZO=y
	CONFIG_SQUASHFS_XZ=y
	CONFIG_SQUASHFS_ZSTD=y
	# CONFIG_SQUASHFS_4K_DEVBLK_SIZE is not set
	# CONFIG_SQUASHFS_EMBEDDED is not set
	CONFIG_SQUASHFS_FRAGMENT_CACHE_SIZE=3

All configs added with a value of y are boolean, hence why they are not m.

Only config-bottlerocket files generated by hand. All other configs generated with make full-config ran on both x86 and aarch64 hosts.

Testing done:

Pod for testing:

Details

apiVersion: v1
kind: Pod
metadata:
  name: test-squashfs
  namespace: default
spec:
  containers:
  - name: test
    image: public.ecr.aws/amazonlinux/amazonlinux:2023
    command:
    - /bin/bash
    - -c
    - |
      set -x

      echo "=== Installing tools ==="
      yum install -y util-linux kmod squashfs-tools procps-ng > /dev/null 2>&1

      echo ""
      echo "=== Kernel version ==="
      uname -r

      echo ""
      echo "=== Check if squashfs module is available ==="
      modprobe squashfs && echo "modprobe squashfs: OK" || echo "modprobe squashfs: FAILED"

      echo ""
      echo "=== Verify module is loaded ==="
      lsmod | grep squashfs

      echo ""
      echo "=== Check /proc/filesystems for squashfs ==="
      cat /proc/filesystems | grep squashfs

      echo ""
      echo "=== Test from issue #4845: mount a dummy squashfs file ==="
      echo "Expected: 'wrong fs type, bad option, bad superblock' (means kernel recognizes squashfs)"
      echo "Failure:  'unknown filesystem type squashfs' (means module not available)"
      for i in 0 1 2 3 4 5 6 7; do mknod -m 660 /dev/loop$i b 7 $i 2>/dev/null || true; done
      truncate -s 4K /tmp/f.sqfs && mkdir -p /tmp/m
      mount -t squashfs -o loop /tmp/f.sqfs /tmp/m 2>&1; echo "exit code: $?"

      echo ""
      echo "=== Test with a real squashfs image ==="
      mkdir -p /tmp/squashfs-root
      echo "hello from squashfs" > /tmp/squashfs-root/hello.txt
      mksquashfs /tmp/squashfs-root /tmp/real.sqfs -noappend -quiet
      mkdir -p /tmp/mnt
      mount -t squashfs -o loop /tmp/real.sqfs /tmp/mnt
      echo "Mount exit code: $?"
      echo "Contents:"
      cat /tmp/mnt/hello.txt
      umount /tmp/mnt

      echo ""
      echo "=== Test compression algorithms ==="
      for algo in gzip lz4 lzo xz zstd; do
        mksquashfs /tmp/squashfs-root /tmp/test-${algo}.sqfs -noappend -quiet -comp ${algo} 2>/dev/null
        if mount -t squashfs -o loop /tmp/test-${algo}.sqfs /tmp/mnt 2>/dev/null; then
          echo "${algo}: OK ($(cat /tmp/mnt/hello.txt))"
          umount /tmp/mnt
        else
          echo "${algo}: FAILED"
        fi
      done

      echo ""
      echo "=== dmesg squashfs entries ==="
      dmesg | grep -i squashfs | tail -10

      echo ""
      echo "=== DONE ==="
      sleep infinity
    securityContext:
      privileged: true
    volumeMounts:
    - name: modules
      mountPath: /lib/modules
      readOnly: true
  volumes:
  - name: modules
    hostPath:
      path: /lib/modules
  restartPolicy: Never
  nodeSelector:
    kubernetes.io/arch: amd64

aws-k8s-1.36-x86_64 (kernel-6.18) and aws-k8s-1.35-x86_64 (kernel-6.12) used for test with the following results:

	Kernel 6.12 (k8s-1.35)	Kernel 6.18 (k8s-1.36)
modprobe squashfs	OK	OK
Issue #4845 test	correct "bad superblock"	correct "bad superblock"
Real mount	OK	OK
gzip	OK	OK
lz4	OK	OK
lzo	OK	OK
xz	OK	OK
zstd	OK	OK

Terms of contribution:

By submitting this pull request, I agree that this contribution is dual-licensed under the terms of both the Apache License, version 2.0, and the MIT license.

[ginglis13]

^ force push moves the module to be in alphabetical order and brings the squashfs config to the top of config-bottlerocket