libunionpreload | Download amd64

This lib tries to create the impression of a union filesystem, effectively creating the impression to the payload application that the specified directory are overlayed over /. This works as long as the payload application is a dynamically linked binary. It also intercepts "execve" calls to ensure that the sub processes also believe that the current directory is overlayed.

How it works in praticle:

export CURRENT_DIRECTORY="$(dirname "$(readlink -f "${0}")")"
export UNION_PRELOAD="/example"
export LD_PRELOAD="${CURRENT_DIRECTORY}/libunionpreload.so"

# If The application try access /usr/lib/bar.so, libunionpreload.so will "replace" 
# the / directory with /example, so, application now is looking for  /example/usr/lib/bar.so,
# if the file exists it is will be used even if the original looking file (/usr/lib/bar.so) exist. 
# If /example/usr/lib/bar.so doesn't exists, the /usr/lib/bar.so is used

How to use

Since it works by reading an environment variable and needs to be preloaded, you will need a bash script with the following lines before running your application:

#!/usr/bin/env sh

export CURRENT_DIRECTORY="$(dirname "$(readlink -f "${0}")")"
export UNION_PRELOAD="${CURRENT_DIRECTORY}"
export LD_PRELOAD="${CURRENT_DIRECTORY}/libunionpreload.so"

# call your application here

How to build

1. Clone repository:

git clone https://github.com/project-portable/libunionpreload.git

2. Enter repository

cd libunionpreload

3. Run make

make

See in action

Run test script:

sh ./test-libunionpreload.sh

Credits

• Michael Terry