TFTP Server

my_busybox=/var/custom/bin/busybox
my_address=192.168.178.1
my_port=69
source_dir=/var/media/ftp
$my_busybox udpsvd -v -c 3 -E $my_address $my_port $my_busybox tftpd -r -l $source_dir

# wget http://yourfritz.de/inject_shellinabox_vr9_nand_sqfs4.tar
# ls -la
drwxr-xr-x    2 root     root          4096 Jan  1 16:08 .
drwxrwxrwx   32 root     root          4096 Jan  1 15:51 ..
-rw-r--r--    1 root     root        539648 Jan  1 15:50 inject_shellinabox_vr9_nand_sqfs4.tar
# tar xvpf inject_shellinabox_vr9_nand_sqfs4.tar
./var/
./var/install
./var/signature
./var/tmp/
./var/tmp/kernel.image
./var/tmp/filesystem.image
# mkdir temp_dir
# mount -t squashfs var/tmp/filesystem.image temp_dir
# find temp_dir
temp_dir
temp_dir/bin
temp_dir[COLOR="#0000FF"]/bin/busybox[/COLOR]
temp_dir/etc
temp_dir/etc/init.d
temp_dir/etc/init.d/rc.custom
temp_dir/lib
temp_dir/lib/libprivatekeypassword.so
temp_dir/usr
temp_dir/usr/bin
temp_dir/usr/bin/privatekeypassword
temp_dir/usr/bin/shellinaboxd

# temp_dir/bin/busybox
BusyBox v1.23.2 (2015-12-15 09:59:22 CET) multi-call binary.
BusyBox is copyrighted by many authors between 1998-2012.
Licensed under GPLv2. See source distribution for detailed
copyright notices.

Usage: busybox [function [arguments]...]
   or: busybox --list
   or: function [arguments]...

        BusyBox is a multi-call binary that combines many common Unix
        utilities into a single executable.  Most people will create a
        link to busybox for each function they wish to use and BusyBox
        will act like whatever it was invoked as.

Currently defined functions:
        [, [[, addgroup, adduser, arp, arping, ash, awk, base64, basename, bash, bbconfig, blkid, blockdev, brctl, bunzip2, bzcat, bzip2, cat, chat, chattr, chgrp, chmod, chown, chpst,
        chroot, cksum, clear, cmp, comm, conspy, cp, cpio, crond, crontab, cryptpw, cttyhack, cut, date, dc, dd, delgroup, deluser, depmod, devmem, df, dhcprelay, diff, dirname, dmesg,
        dnsd, dnsdomainname, dos2unix, dpkg, dpkg-deb, du, dumpleases, echo, egrep, env, envdir, envuidgid, ether-wake, expand, expr, false, fatattr, fdisk, fgconsole, fgrep, find,
        findfs, flash_eraseall, flash_lock, flash_unlock, flashcp, flock, fold, free, fsck, fsync, ftpd, ftpget, ftpput, fuser, getopt, grep, groups, gunzip, gzip, halt, hd, hdparm, head,
        hexdump, hostid, hostname, httpd, id, ifconfig, ifdown, ifenslave, ifup, inetd, init, inotifyd, insmod, install, iostat, ip, ipaddr, ipcalc, ipcs, iplink, iproute, iprule,
        iptunnel, kill, killall, killall5, klogd, last, less, ln, logger, login, logname, logread, losetup, ls, lsattr, lsmod, lsof, lspci, lsusb, lzcat, lzma, makedevs, makemime, md5sum,
        microcom, mkdir, mkfifo, mknod, mkpasswd, mkswap, mktemp, modinfo, modprobe, more, mount, mountpoint, mpstat, mv, nanddump, nandwrite, nbd-client, nc, netstat, nice, nmeter,
        nohup, nslookup, ntpd, od, openvt, passwd, patch, pgrep, pidof, ping, ping6, pipe_progress, pivot_root, pkill, pmap, poweroff, printenv, printf, ps, pscan, pstree, pwd, pwdx,
        rdate, rdev, readlink, realpath, reboot, reformime, renice, reset, rev, rfkill, rm, rmdir, rmmod, route, rpm, rpm2cpio, run-parts, runsv, runsvdir, rx, sed, sendmail, seq,
        setconsole, setlogcons, setserial, setsid, setuidgid, sh, sha1sum, sha256sum, sha3sum, sha512sum, shuf, slattach, sleep, smemcap, softlimit, sort, split, start-stop-daemon, stat,
        strings, stty, stun-ip, sv, svlogd, swapoff, swapon, switch_root, sync, sysctl, syslogd, tac, tail, tar, taskset, tcpsvd, tee, telnet, telnetd, test, tftp, [COLOR="#0000FF"]tftpd[/COLOR], time, timeout,
        top, touch, tr, traceroute, traceroute6, true, tty, tunctl, tune2fs, ubiattach, ubidetach, ubimkvol, ubirmvol, ubirsvol, ubiupdatevol, udhcpc, udhcpc6, udhcpd, udpsvd, umount,
        uname, unexpand, uniq, unix2dos, unlink, unlzma, unxz, unzip, uptime, users, usleep, uudecode, uuencode, vconfig, vi, watch, watchdog, wc, wget, which, who, whois, xargs, xz,
        xzcat, yes, zcat, zcip
#

# temp_dir/bin/busybox tftpd
BusyBox v1.23.2 (2015-12-15 09:59:22 CET) multi-call binary.

Usage: tftpd [-cr] [-u USER] [DIR]

Transfer a file on tftp client's request

tftpd should be used as an inetd service.
tftpd's line for inetd.conf:
        [COLOR="#0000FF"]69 dgram udp nowait root tftpd tftpd -l /files/to/serve[/COLOR]
It also can be ran from udpsvd:
        udpsvd -vE 0.0.0.0 69 tftpd /files/to/serve

        -r      Prohibit upload
        -c      Allow file creation via upload
        -u      Access files as USER
        -l      Log to syslog (inetd mode requires this)
#

# ls -la /etc/inetd.conf
lrwxrwxrwx    1 root     root            21 Dec 10 19:23 /etc/inetd.conf -> ../var/tmp/inetd.conf
# cat /etc/inetd.conf
21 stream tcp6 nowait.30 root /bin/sh sh /bin/inetdftp
139 stream tcp6 nowait root /bin/sh sh /bin/inetdsamba
445 stream tcp6 nowait root /bin/sh sh /bin/inetdsamba
#
# mkdir /var/media/ftp/bin
# cp -p bin/busybox /var/media/ftp/bin/busybox_pp
# mkdir /var/media/ftp/tmp
#
# vi /etc/inetd.conf
21 stream tcp6 nowait.30 root /bin/sh sh /bin/inetdftp
139 stream tcp6 nowait root /bin/sh sh /bin/inetdsamba
445 stream tcp6 nowait root /bin/sh sh /bin/inetdsamba
[COLOR="#0000FF"]69 dgram udp nowait root /var/media/ftp/bin/busybox_pp tftpd -l /var/media/ftp/tmp[/COLOR]

# ps | grep inetd
 [COLOR="#0000FF"]3111[/COLOR] root      1376 S    /usr/sbin/inetd
 6134 root      1372 S    grep inetd
# kill -SIGHUP [COLOR="#0000FF"]3111[/COLOR]
#