Andrés J. Díaz

bashc

A tool to convert/compile a bash script to a static linked x86 and x86_64 binary.

Latest stable relases:

Source:releases/bashc-1.0.tar.gz
Signature:releases/bashc-1.0.tar.gz.asc

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Contents:


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 he 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.


CONTRIBUTE

If you find any error in the code or incorrect behaviour, please do not hesitate to report me at ajdiaz+bashc at ajdiaz.me.

The mainstream code is keep under git control, you can clone as usual:

git clone git://git.ajdiaz.me/ajdiaz/bashc.git

Also you can open a issue in github mirror.


Andrés J. Díaz <ajdiaz at ajdiaz.me>.
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