backhand

Library and binaries for the reading, creating, and modification of SquashFS file systems.

• Library — Backhand provides an easy way for programmatic analysis of Squashfs 4.0 images, including the extraction and modification of images.

• Feature Flags — Supported compression and decompression are feature flagged, so your final binary (or unsquashfs) only needs to include code to extract one type of image.

• Unconventional Support — As well as supporting normal linux kernel SquashFS 4.0, we also support the "wonderful world of vendor formats" with a Kind struct. This allows changing the magic bytes, custom compression algorithms, and the Endian-ness of either the Data or Metadata fields.

Library

Compiler support: requires rustc 1.72.1+

Add the following to your Cargo.toml file:

[dependencies]
backhand = "0.19.0"

Target Support

Although additional targets may be supported, only the following have been fully tested or confirmed to build successfully.

Reading/Writing/Modifying Firmware

use std::fs::File;
use std::io::{Cursor, BufReader};
use backhand::{FilesystemReader, FilesystemWriter, NodeHeader};

// read
let file = BufReader::new(File::open("file.squashfs").unwrap());
let read_filesystem = FilesystemReader::from_reader(file).unwrap();

// convert to writer
let mut write_filesystem = FilesystemWriter::from_fs_reader(&read_filesystem).unwrap();

// add file with data from slice
let d = NodeHeader::default();
let bytes = Cursor::new(b"Fear is the mind-killer.");
write_filesystem.push_file(bytes, "a/d/e/new_file", d);

// add file with data from file
let new_file = File::open("dune").unwrap();
write_filesystem.push_file(new_file, "/root/dune", d);

// modify file
let bytes = Cursor::new(b"The sleeper must awaken.\n");
write_filesystem.replace_file("/a/b/c/d/e/first_file", bytes).unwrap();

// write into a new file
let mut output = File::create("modified.squashfs").unwrap();
write_filesystem.write(&mut output).unwrap();

Binaries

Compiler support: requires rustc 1.77+

These are currently under development and are missing features, MR's welcome!

To install, run cargo install backhand-cli --locked, or download from the latest github release.

See --help for more information.

Target Support

Although additional targets may be supported, only the following have been tested and included in our GitHub releases.

unsquashfs-backhand

tool to uncompress, extract and list squashfs filesystems

Usage: unsquashfs-backhand [OPTIONS] [FILESYSTEM]

Arguments:
  [FILESYSTEM]  Squashfs file

Options:
  -o, --offset <BYTES>             Skip BYTES at the start of FILESYSTEM [default: 0]
  -a, --auto-offset                Find first instance of squashfs --kind magic
  -l, --list                       List filesystem, do not write to DEST (ignores --quiet)
  -d, --dest <PATHNAME>            Extract to [PATHNAME] [default: squashfs-root]
  -i, --info                       Print files as they are extracted
      --path-filter <PATH_FILTER>  Limit filesystem extraction [default: /]
  -f, --force                      If file already exists then overwrite
  -s, --stat                       Display filesystem superblock information (ignores --quiet)
  -k, --kind <KIND>                Kind(type of image) to parse [default: le_v4_0] [possible
                                   values: be_v4_0, le_v4_0, avm_be_v4_0]
      --completions <COMPLETIONS>  Emit shell completion scripts [possible values: bash, elvish,
                                   fish, powershell, zsh]
      --quiet                      Silence all progress bar and RUST_LOG output
  -h, --help                       Print help (see more with '--help')
  -V, --version                    Print version

add-backhand

tool to add a file or directory to squashfs filesystems

Usage: add-backhand [OPTIONS] <INPUT_IMAGE> <FILE_PATH_IN_IMAGE> <OUTPUT_IMAGE>

Arguments:
  <INPUT_IMAGE>         Squashfs input image
  <FILE_PATH_IN_IMAGE>  Path of file once inserted into squashfs
  <OUTPUT_IMAGE>        Squashfs output image path

Options:
  -d, --dir                     Create empty directory
  -f, --file <FILE>             Path of file to read, to write into squashfs
      --mode <MODE>             Override mode read from <FILE>
      --uid <UID>               Override uid read from <FILE>
      --gid <GID>               Override gid read from <FILE>
      --mtime <MTIME>           Override mtime read from <FILE>
      --pad-len <PAD_LEN>       Custom KiB padding length
      --no-compression-options  Don't emit compression options
  -h, --help                    Print help
  -V, --version                 Print version

replace-backhand

tool to replace files in squashfs filesystems

Usage: replace-backhand [OPTIONS] <INPUT_IMAGE> <FILE> <FILE_PATH_IN_IMAGE> <OUTPUT_IMAGE>

Arguments:
  <INPUT_IMAGE>         Squashfs input image
  <FILE>                Path of file to read, to write into squashfs
  <FILE_PATH_IN_IMAGE>  Path of file replaced in image
  <OUTPUT_IMAGE>        Squashfs output image

Options:
      --pad-len <PAD_LEN>       Custom KiB padding length
      --no-compression-options  Don't emit compression options
  -h, --help                    Print help
  -V, --version                 Print version

Performance

See BENCHMARK.md.

Testing

See backhand-test.