reset-firmware

#!/bin/sh

# display warn message, wait for user confirmation before continuing
echo -n "erase all settings and remove any installed packages? [N/y] ">&2 && read
[ "${REPLY}" != "y" ] && exit 1

# check firmware mount state to then delete data accordingly
if egrep -qs "^overlayfs:/firmware " /proc/mounts; then
    # inform user about firmware mount state and action taken to reset rootfs_data
    echo "firmware is mounted, only erasing files">&2

    # erase all files (including "dot" and "dot-dot" files)
    rm -rf /firmware/overlay/upper/*
    rm -rf /firmware/overlay/upper/.[^.]*
    rm -rf /firmware/overlay/upper/..?*
else
    # inform user about firmware mount state and action taken to reset rootfs_data
    echo "firmware not mounted, marking it to be erased on next mount">&2

    # find firmware mtd partition
    firmware=$(grep '"firmware"' /proc/mtd | cut -d: -f1)
    firmware_size=$(cat /sys/class/mtd/${firmware}/size)
    firmware_blocksize=$(cat /sys/class/mtd/${firmware}/erasesize)

    # initialize rootfs_data search variables
    rootfsdata_marker="(deadc0de|1985)"
    rootfsdata_offset=0

    # search for rootfs_data inside firmware mtd partition
    while [ ${rootfsdata_offset} -lt ${firmware_size} ]; do
        # dump four bytes at offset (as hexadecimal string) and check if matches the marker pattern
        if hexdump -e '"%x"' -n 4 -s ${rootfsdata_offset} /dev/${firmware} | egrep -qs "^${rootfsdata_marker}"; then
            # marker found, break loop
            break
        fi
        # continue searching, move to the next mtd block
        rootfsdata_offset=$((rootfsdata_offset + firmware_blocksize))
    done

    # write jffs2 marker (0xdeadc0de) to force initialization of rootfs_data on the next mount
    echo -ne "\xde\xad\xc0\xde" | dd of=/dev/mtdblock${firmware:3} bs=${firmware_blocksize} seek=$((rootfsdata_offset / firmware_blocksize)) count=1 conv=sync &>/dev/null
fi