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OpenWRT and Perl


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Wherein I install OpenWRT on to an inexpensive TP-Link pocket router, install perl and attempt to smoke CPAN.

I also introduce OpenWRT in possibly too much detail, and dont really explain what smoking CPAN is.

Published in: Technology
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OpenWRT and Perl

  1. 1. OpenWRT and Perl (Because, why not smoke CPAN on your home’s router?) Dean Hamstead
  2. 2. This ‘LCARS’ like slide theme was just a choice on Google docs. It’s not a statement on Star Trek vs Star Wars. If pressed, my thoughts on Star Trek vs Star Wars are as follows... Dislcaimer
  3. 3. An introduction to OpenWRT Installing Perl Smoking CPAN You all go home and brick your routers Overview
  4. 4. Linux distro Aimed at IP routers and Access Points Originated from Linksys’s infamous WRT54G Started 2004 Kernel is kept parallel to mainline Lot’s goes upstream, wifi related especially, but no sense in mainlining code for quirks in just one modem model Release names are alcoholic beverages OpenWRT in a nutshell
  5. 5. Userland is ash, uClibc and BusyBox with lots of Lua scripts opkg package suite Unified Config. Interface (UCI) Configures everything in one place - /etc/config Use vim, and/or CLI and GUI tools Easy to backup/migrate all your config! OpenWRT in a nutshell (cont.)
  6. 6. Similar Projects/Products DD-WRT Some devices require a license Tomato Firmware Based on HyperWRT LibreCMC OpenWRT minus binary blobs
  7. 7. Quick Start Buy a compatible router Find & download the correct image file Then install it...
  8. 8. Flash the firmware via “upgrade”
  9. 9. Log in for the first time The router/AP hands out IP’s via DHCP by default Watch out for that! Telnet (yes, telnet) to to log in as root Set root’s password with ‘passwd’ and telnet will be automatically and forever disabled Log back in as root via ssh
  10. 10. Now you can do stuff! See also That’s it!
  11. 11. Ok, let’s dive in deeper...
  12. 12. SoC - System on a Chip. The CPU + whatever is on the same die PCB - Printed Circuit Board TTL - Transistor-Transistor Logic. Serial done differently is all you need to know Pin Headers (header) - Pins you can attach too on the PCB. Sometimes you have to solder them on. JTAG - Colloquialism for the TTL headers on the modems PCB Important Terms
  13. 13. From: Router Structure 101
  14. 14. Like Router, but without the Switch bit Access Point Structure 101
  15. 15. From: Router Structure 202
  16. 16. On embedded devices a “bootloader” initializes the hardware then loads the kernel. Bootloader->Kernel Contrast to the PC with BIOS->Grub->Kernel Das U-Boot (GPL) is the most common IMO It has lots of nice features, especially for recovery Vendors tend to mess with the bootloader Arbitrary kernel size limits Magic values need to be present in the kernel Require some exotic firmware format Don’t support ELF See also The Bootloader
  17. 17. Most modems and routers are the MIPS architecture, as opposed to x86 or AMD64 “Microprocessor without Interlocked Pipeline Stages” Good performance/cost/power ratios RISC, simple instructions, frequently studied in Universities (I had to write a mips VM) Manufacturers make various changes for whatever reason, which results in lots of “sub” architectures OpenWRT also supports ARM, PowerPC and x86’s See Let’s learn about Architectures
  18. 18. Let’s learn about flash Routers have flash rather than HDD, which serves the same purpose When flash directly attached to the SoC, OpenWRT calls it “raw flash” When there is a chip between the SoC and the flash (like an SSD or USB), OpenWRT calls this a “Flash Translation Layer” Older routers usually have NOR flash Newer routers have NAND flash NAND can tolerate errors, though Linux still can’t Linux and hence OpenWRT, utilize raw flash via the “Memory Technology Device” layer and a special purpose FS More flash is always good, you can install more stuff! You will likely want to use one of OpenWRT two main flash formats, SquashFS or JFFS2 See also See also
  19. 19. SquashFS is a read-only LZMA compressed file system. In this image type, OpenWRT stores the system in SquashFS partition, then uses a JFFS2 partition to overlay changes JFFS2 is r/w and also LZMA compressed, but SquashFS is 20-30% smaller. Includes wear leveling and Journalling. This OpenWRT image type just has one partition SquashFS vs JFFS2
  20. 20. +less space +failsafe recovery - read only - uses more space over time SquashFS JFFS2 +r/w, journaling and wear leveling +compression saves space - … but actual space usage difficult to estimate before writing files - no failsafe recovery
  21. 21. SquashFS is a good choice for beginners as you can “factory reset”. So let’s just plan to download a SquashFS image once you’ve picked out a router as your first victim. Which we will do now... So… SquashFS or JFFS2?
  22. 22. Firstly: Throw away all your preconceptions about “good” and “bad” router brands. They are all just a SoC + RAM + Flash on a PCB mounted inside a plastic case. Who cares how woeful the vendor firmware is, it won’t be on there for long! Don’t spend extra $ on the same SoC Picking a Router / AP device
  23. 23. A compatible Router or AP Linksys WRT54G is too old now. Avoid it. Netgear & TP-Link are readily available in Australia. Check compatibility BEFORE you buy! There’s no consistency with compatibility at all. Even between model revisions! Netgear WNR3500Lv1 is a good choice. Alas you’ll need to order online or via eBay.
  24. 24. If listed as supported on OpenWRT wiki, it’s supported If listed as absolutely no chance (i.e. due to SoC or low flash), it’s not supported Anything in between it may be supported via nightlies Search their forums, their change log and commit history Don’t be offput by nightlies Check BEFORE you buy A compatible Router or AP (cont.)
  25. 25. OpenWRT ships nightly builds and “stable” releases Nightlies will support the latest and greatest Major stable releases seem to be roughly annual, with minor updates in between Stable release version numbers are the year and month of issue. (An additional third number indicates a service or interim release from that branch) LUCI web interface isn’t included in nightlies (not a huge loss) I’ve had as much success with nightly builds as with stable, so no need to be sheepish Naturally, YMMV Nightlies, what?
  26. 26. Netgear WNR3500L v1 Ubiquiti UniFi AP’s TP-Link TL-WR703N, TL-WDR3500/3600 See also: Suggested Devices
  27. 27. Yes, OpenWRT runs on Raspberry Pi! A, B, B+, B2 all supported WiFi + 2nd NIC via USB (Miserable performance IMO) See also What about Raspberry Pi?
  28. 28. Older modems might not be able to sustain ‘modern’ (NBN, Cable, FTTN) speeds LAN to WAN, irrespective of the port connection speed The original Linksys WRT54G could only manage 30mbps LAN2WAN I also recommend making any serious use of the built in switch, they usually suck. Note!
  29. 29. 99.9% OpenWRT has no ADSL support Traverse Technologies has a Geode (x86!) based dual ADSL modem with fully FOSS ADSL. A little pricy but only just outside impulse buy IMO. ADSL?
  30. 30. Netgear released a GPL driver in their code drop for their VEVG2500 device. It uses the Lantiq VR9 SoC and was only released in France? Good news! the TP-W8970 & TP-W8980 use the same SoC Supports both VDSL and ADSL2+ ! ADSL? (cont.)
  31. 31. You’re mostly out of luck, cable modems tend to run eCos and have fun getting source Get a cable modem with bridge mode, connect to it an IP router with OpenWRT Optus (and Telstra?) currently only ship NATing modems, so you’ll have to head to eBay. Far be it for me to EVER recommend Cisco Products. But for Optus I do recommend the Cisco DPQ3212 if you can find it. It’s DOCSIS 3.0 for 100mbps+. Cable? (DOCSIS)
  32. 32. Buy a set of Torx Screwdrivers from Jaycar or online Alas you can’t really just buy 1 You’ll need these to open up your modem when... Torx Screwdrivers
  33. 33. inevitable brick your modem. Not a big deal Modems usually have a 3.3v TTL console header inside Purchase a USB Serial to TTL off of eBay for a few dollars Buy the cheapest you can find Linux supports w/ in kernel driver, Windows not so much I recommend moulded with floating pin sockets as pictured Also available are pure PCB, or actual RS232 to TTL converters USB Serial to TTL
  34. 34. More on installation...
  35. 35. Use web interface for “upgrade”
  36. 36. The Ubiquiti UniFi AP’s can be upgraded via scp+ssh, as can many other devices Some devices require a special intermediate image which is either signed or somehow breaks out of vendor lock in Refer to the OpenWRT Wiki page for your modem! … or via CLI
  37. 37. Other modems you will need to attach your TTL cable and get into the bootloader Yet other modems will allow you to hold the reset button and put them into a “brain load” mode From either of the above, you can then feed in an OpenWRT image via tftp. Good times. ...or via serial and/or tftp
  38. 38. Bricking isn’t a big deal (I 99% promise) If you brick your router due to config, with SquashFS you can just “factory reset” back to vanilla OpenWRT Reminder: back up /etc/config If you brick during upgrade: “Failsafe” reload is a common function of U-Boot devices. Hold down reset, power on, then tftp upload firmware Otherwise you will need to use your TTL cable... Rescuing your bricked router
  39. 39. Sometimes needed to load Often needed to de-brick Carelessness can release the magic black smoke inside the chips. No magic = no modem. be careful Unlike in movies, the colors of the TTL wires are basically random If you have 4 wires, attach to USB and use a volt-meter to determine which one is +5V Mark it clearly Plugging it to your device will almost certainly release the genie. So don’t plug it to your device. Connecting your TTL Cable
  40. 40. If you’re lucky the pins are labeled or documented on online (i.e. OpenWRT wiki) Some online reference may tell you the BAUD rate. Set that in your terminal software. Else start with 19200 or 38400 I like cu and gtkterm. minicom not so much. putty has great serial support too Turn on your modem, and try the different wires on each pin until you get something meaningful on your screen Mark that pin as “out” on the pcb and “rx” on the wire Repeat for “in” / “tx” - mash keys and look for screen changes The remaining wire & pin is ground. Mark that too I suggest you take a photo for good measure ----> Optionally, make it a permanent fixture by drilling a small hole in the case and feeding the cable through, then tying a small knot in the cable on the inside to secure it. Maybe use a glue gun too Connecting your TTL Cable (cont.)
  41. 41. Doing stuff via TTL When you boot the device, you will see it POST and boot. If it’s bricked you will see some of that For Atheros, BIOS is usually ‘Das U-Boot’ You can set an IP (or DHCP) then pull a tftp file to boot. Something like: setenv ipaddr setenv serverip setenv bootargs 'board=WNDR3700' tftpboot 80800000 openwrt-fixed.out bootm
  42. 42. Now What? On to Perl
  43. 43. Micro Perl Smoker, B.O.M. TP-Link TL-WR703N (not the 702!!) A USB thumb drive A Linux machine Too much spare time
  44. 44. Just get it from eBay Generally it will come from Asia with a transformer unsuited to our Australian wall sockets… but it’s just micro-USB (like on most Android phones) Acquire TL703N
  45. 45. Get the “Chaos Calmer” stable release from: er/15.05/ar71xx/generic/ You’ll want the 703n...factory.bin file Revisions prior to 1.7, just use the GUI to flash 1.7 is a pain Flash TL703N
  46. 46. Copy and paste non-english menus to Google translate. Or guess from the URL. Flash TL703N (cont.)
  47. 47. For version 1.7, follow the steps on Basically, you will split the openwrt image into two pieces using ‘dd’. Set up a tftp server. Then exploit a bug in the web interface to download and overwrite the vendor firmware… using curl. It’s actually not too bad! Flash TL703N (cont.)
  48. 48. Plug your Linux PC via Ethernet to the TL703N Get an IP via DHCP Telnet to Use ‘passwd’ to set a password (telnet is now disabled and ssh enabled) Logout, then ssh root@ Optionally, configure WiFi as a client See also Follow first install steps
  49. 49. Insert drive to your linux PC fdisk /dev/sdX set to type 83 mkfs.ext4 /dev/sdX1 remove thumbdrive Format your thumb drive
  50. 50. The TL703N doesn’t have enough space, so we pack a custom image without PPP and plus usb+ext4 Pack not compile - OpenWRT provides nice tools for this purpose Image Generate (was Image Builder) Learn more Pack a custom OpenWRT image
  51. 51. cd ~; mkdir openwrt; cd openwrt wget ImageBuilder-15.05-ar71xx-generic.Linux-x86_64.tar.bz2 tar -xvjf OpenWrt-ImageBuilder-15.05-ar71xx-generic.Linux-x86_64.tar.bz2 make image PROFILE=TLWR703 PACKAGES="blkid block-mount kmod-fs-ext4 kmod-usb2 kmod- usb-uhci kmod-usb-ohci kmod-usb-storage -ppp -kmod-ppp -ppp-mod-pppoe -kmod-pppoe - kmod-pppox" cd bin/71xx scp *sysupgrade.bin root@ ssh root@ cd /tmp sysupgrade *bin … thats it! Packing Steps
  52. 52. There still isn’t enough space. So we set the root to the external drive (ExtRoot). First plug in the USB drive, then: ssh root@ mount /dev/sda1 /mnt ; tar -C /overlay -cvf - . | tar -C /mnt -xf - ; umount /mnt echo -e "config 'global'ntoption anon_swap '0'ntoption anon_mount '1'ntoption auto_swap '1'ntoption auto_mount '1'ntoption delay_root '5'ntoption check_fs '0'nnconfig 'mount'ntoption target '/'ntoption enabled '1'ntoption device '/dev/sda1'n" > /etc/config/fstab # read more at reboot # if something seems fishy, it’s safe to start up the TL703N without the usb, and it will fallback to the onboard flash Make system ExtRoot
  53. 53. root@MiniOpenWrt:~# df -h Filesystem Size Used Available Use% Mounted on rootfs 3.6G 7.7M 3.4G 0% / /dev/root 2.3M 2.3M 0 100% /rom tmpfs 14.0M 68.0K 14.0M 0% /tmp /dev/sda1 3.6G 7.7M 3.4G 0% /overlay overlayfs:/overlay 3.6G 7.7M 3.4G 0% / tmpfs 512.0K 0 512.0K 0% /dev /dev/mtdblock3 640.0K 244.0K 396.0K 38% /mnt/mtdblock3 Hooray we have more space!
  54. 54. Trivia: OpenWRT breaks core perl up into very small pieces… infact, ridiculously so. However, this means you can be very frugal with the tiny space you have available.
  55. 55. # Note the double >> echo -e "src/gz chaos_calmer_base z chaos_calmer_packages rc/gz chaos_calmer_routing c/gz chaos_calmer_management n" >> /etc/opkg.conf opkg update opkg install perl perlbase-cpan perlbase-unicore perlbase-dynaloader perlbase-term perlbase-perlio perlbase-if perlbase-universal perlbase-getopt # optionally... opkg install screen wget # things are looking good! Install a Perl
  56. 56. perl -MCPAN -e shell > install CPAN::Reporter ##### OH GNOES KILLED!!!!! ##### dmesg | tail -5 # [160707.320000] Out of memory: Kill process 3501 (perl) score 529 or sacrifice child # [160707.330000] Killed process 3501 (perl) total-vm:19836kB, anon-rss:15568kB, file-rss:80kB Not surprising really... > egrep 'Swap|^Mem' /proc/meminfo MemTotal: 28740 kB MemFree: 13472 kB MemAvailable: 15580 kB SwapCached: 0 kB SwapTotal: 0 kB SwapFree: 0 kB Install a CPAN Smoker...
  57. 57. # its like windows all over again dd if=/dev/zero of=/swapfile bs=1M count=1024 # because hax00rs chmod 600 /swapfile mkswap /swapfile # that url again echo -e “nconfig ‘swap’noption device ‘/swapfile’n” swapon /swapfile # win! - note: swap on a USB thumb drive will thrash it > grep Swap /proc/meminfo SwapCached: 0 kB SwapTotal: 524284 kB SwapFree: 524284 kB Quick, add a swap file
  58. 58. perl -MCPAN -e shell > install CPAN::Reporter # wait a long long time ##### OH GNOES KILLED!!!!! ##### dmesg | tail -5 # [160707.320000] Out of memory: Kill process 3501 (perl) score 529 or sacrifice child # [160707.330000] Killed process 3501 (perl) total-vm:19836kB, anon-rss:15568kB, file-rss:80kB And now the dramatic, unexpected twist! Try CPAN again
  59. 59. I haven’t solved why OOM keeps killing it! I suspect: /tmp (tmpfs) is chewing up “RAM” Whilst perl is also chewing up “RAM” I will need a bigger USB stick or several USB sticks on a USB hub to experiment further.
  60. 60. Questions?
  61. 61. http://www.linux- Watt-Server Others? Useful links