https://github.com/ajdiaz/bashc

A tool to convert/compile a bash script to a static linked x86 and x86_64 binary.
https://github.com/ajdiaz/bashc

Last synced: 6 days ago
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A tool to convert/compile a bash script to a static linked x86 and x86_64 binary.

• Host: GitHub
• URL: https://github.com/ajdiaz/bashc
• Owner: ajdiaz
• License: gpl-3.0
• Created: 2016-10-18T20:21:01.000Z (about 8 years ago)
• Default Branch: master
• Last Pushed: 2023-03-06T18:30:07.000Z (over 1 year ago)
• Last Synced: 2024-08-02T16:05:44.419Z (3 months ago)
• Language: Shell
• Homepage: https://ajdiaz.me/bashc/
• Size: 46.9 KB
• Stars: 31
• Watchers: 2
• Forks: 5
• Open Issues: 2
• Metadata Files:
  • Readme: README
  • License: LICENSE

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README

        
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BashC is a tool which get your bash script and produces an static linked

binary for Linux x86 and x86_64 machines (also support ARM and many other

OS, but I cannot test them yet) which runs your script.

For example:

  $ cat > myscript.sh << EOF

  #!/bin/bash

  echo "This is a test

  EOF

  $ bashc myscript.sh myscript.bin

  $ file myscript.bin

  bashc: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), statically

  linked, stripped

  $ ./myscript.bin

  This is a test

Nice eh!

---- Installation --------------------------------------------------------

From source code just run:

  make

Easy :)

---- Internals ----------------------------------------------------------

This application is based on previous work from Robert Xu¹, which uses musl

instead of glibc avoiding calls to dlopen(3) to produce a static binary.

I added some patches (in patch/ directory) to convert the bash binary in

a compiler tool. The patch does the following:

1. Read the filesize of itself and jump (lseek) to the last byte of the

   binary.

2. There read -20 chars as decimal number which represents the length of the

   script to be executed

3. Jump again (lseek) to END - length readed in (2)

4. Bash interpret the code in current fd position.

That is how bashc runs a script. To create the binary just concatenate to the

static patched bash, the script to run. Because of ELF header (and in theory

also Match) ensure us that execution will never reads after lenght scecified

in ELF header, then our script still safe after that position. During the

execution the algorithm explained above is running and the script is

interpreted.

¹ https://github.com/robxu9/bash-static

---- Limitations --------------------------------------------------------

* Not tested in any other platform than Linux X86 and X86_64.

* The bash script code is concatenated in plain text, so no security here.

* We cannot use any external dependency for the script unless it was

  previously compiled as builtin.

* If you call bashc from exec syscall, please use the full path to the

  binary (prefixing current working directory if needed) to avoid problems

  during the binary generation. Althoug the generated binary works fine

  in any path (is script is designed for that), the compilation itself does not.