Shared Library to intercept nvram get/set/match calls for emulating libnvram.so used by many IoT firmware software. I first wrote this library to intercept nvram calls made by software running on the Netgear Nighthawk R6250 and R6400 routers, for emulating them under QEMU.

Loosely based on Craig Heffner @devttyS0 and Zachary Cutlip @zcutlip's work.

To compile custom_nvram_r6250.so from custom_nvram_r6250.c, we need buildroot.

buildroot/output/host/usr/bin/arm-buildroot-linux-uclibcgnueabi-gcc -shared -fPIC -o custom_nvram_r6250.so custom_nvram_r6250.c

Invocation

PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
     LD_PRELOAD=/tmp/custom_nvram_r6250.so
     /usr/sbin/httpd -S -E /usr/sbin/ca.pem /usr/sbin/httpsd.pem

custom_nvram_r6250.so will look for a hardcoded file /tmp/nvram.ini containing the configuration data.

coming soon

References:

• https://github.com/zcutlip/nvram-faker
• http://tldp.org/HOWTO/Program-Library-HOWTO/shared-libraries.html
• https://stackoverflow.com/questions/9759880/automatically-executed-functions-when-loading-shared-libraries
• https://gcc.gnu.org/onlinedocs/gcc/Return-Address.html