Block Syscall

This repository contains code to compile a Linux Kernel Module that will create a device (/dev/block_syscall_dev) with a blocking (forever) operation on open syscall.

The goal of this is to reproduce a bug where the process blocking in the syscall turns zombie after being killed although there is a parent to waitpid on the zombie process.

For that purposes, a userland application is available in that repository. It launches a thread which will open the device blocking.

If an application open the devices directly from the main (sudo cat /dev/syscall_dev for instance), killing the cat process does not turn it into zombie because the process is in D state (uninteruptible sleep).

Usage

x86

make
sudo insmod block_syscall.ko
sudo ./userland

Beware, you will not be able to kill userland (TERM or KILL). The only way out is to poweroff the host, for that reason it is recommended to test is inside a Virtual Machine.

R4IP

First store r4ip buildroot directory path into a variable:

export R4IP_DIR=<path to r4ip-buildroot>

Compile userland application:

CC=${R4IP_DIR}/output/host/bin/powerpc-buildroot-linux-gnu-gcc make userland

Compile Linux Kernel Module:

PATH="${R4IP_DIR}/output/host/bin:${R4IP_DIR}/output/host/sbin:${PATH}" BUILD_KERNEL="ce047afcbfcd6bc92e386cce5beb6e33ac725695" KSRC="${R4IP_DIR}/output/build/linux-ce047afcbfcd6bc92e386cce5beb6e33ac725695" KMOD="${R4IP_DIR}/output/target/lib/modules/ce047afcbfcd6bc92e386cce5beb6e33ac725695" /usr/bin/make -j13 -C $(pwd) HOSTCC="/usr/bin/gcc -O2 -I${R4IP_DIR}/output/host/include -L${R4IP_DIR}/output/host/lib -Wl,-rpath,${R4IP_DIR}/output/host/lib" ARCH=powerpc INSTALL_MOD_PATH=${R4IP_DIR}/output/target CROSS_COMPILE="${R4IP_DIR}/output/host/bin/powerpc-buildroot-linux-gnu-" DEPMOD=${R4IP_DIR}/output/host/sbin/depmod INSTALL_MOD_STRIP=1 module

Make sure that kernel version is up to date.

references:

Processes states