See https://github.com/eunomia-bpf/bpf-developer-tutorial/tree/main/src/27-replace for the full source code.

Compile:

make

Usage:

sudo ./replace --filename /path/to/file --input foo --replace bar

This program will replace all text in the file that matches 'input' with 'replace' text. There are many use cases for this, such as:

Hiding the kernel module 'joydev' to avoid detection by tools like 'lsmod':

./replace -f /proc/modules -i 'joydev' -r 'cryptd'

Spoofing the MAC address of the 'eth0' interface:

./replace -f /sys/class/net/eth0/address -i '00:15:5d:01:ca:05' -r '00:00:00:00:00:00'

Malware performing anti-sandbox checks may look for MAC addresses as an indication of whether it is running in a virtual machine or sandbox, rather than on a "real" machine.

Note: The lengths of 'input' and 'replace' must be the same to avoid introducing NULL characters in the middle of the text block. To input a newline character at a bash prompt, use $'\n', for example --replace $'text\n'.

• https://github.com/pathtofile/bad-bpf.