diff --git a/enforcement-case-studies.tex b/enforcement-case-studies.tex index e76a55a8cfa7689a78cdbb00939a6cef14dc82be..98dade6e8d4d7e907a6dabf1f28ebf282e92f4bf 100644 --- a/enforcement-case-studies.tex +++ b/enforcement-case-studies.tex @@ -597,59 +597,113 @@ compilation). %same directory at thinkpenguin_librecmc-built-busybox_output.log - you may want %to only use part of the BusyBox output (maybe even just the login) for brevity -%% \section{U-Boot Installation} - -%% The U-Boot installation process is substantially more complicated than the -%% firmware update. The investigator purchased the optional a serial cable -%% along with the TPE-NWIFIROUTER, in order to complete the U-Boot installation -%% per the instructions in'' -boot\verb0_0reflash''. - -%% However, we were -%% only able to read data from the serial port; we were unable to interrupt the -%% boot process or access the U-Boot console to complete the U-Boot re-flash. Here -%% are the steps we tried: - -%% * We found the serial cable included was a USB serial adapter that had a male -%% USB type A connector on one end and 4 female jumper wires at the other end. -%% These female jumper wires were red, black, white, and green. -%% * The instructions did not specify how to connect these wires, but we were able -%% to determine this in part using the "v8.4" image (close to our "v8.2" router) -%% at \url{http://wiki.openwrt.org/toh/tp-link/tl-wr841nd#serial.console} . Aside from -%% power and ground (red and black), we did have to guess which of the wires was -%% RX and TX. By experimentation we found that green was RX and white was TX. -%% When we tried the other way, we received no data to our serial console at boot -%% time. -%% * We did have to use the included jumper pin gender changer with the USB serial -%% adapter, which we put through the holes on the router's mainboard and then -%% connected to the USB serial adapter. The fit was fairly loose so it would be -%% nice if future router versions included a tighter gender changer or (ideally) -%% had the jumper pins soldered onto the board to begin with (so no gender -%% changer would be required). -%% * We used 115200 8N1 as our serial console settings (with no hardware or -%% software flow control). This was tested with both the minicom and screen -%% commands. We found that if we connected all 4 wires on the USB serial adapter -%% that the router would start without additional power and our console would -%% receive the startup messages. We could replicate the same behavior by -%% omitting the power cable from the USB serial adapter (red wire) and connecting -%% the main power adapter to the router instead. -%% * While we did see the U-Boot and kernel boot logs in our serial console, we -%% were unable to interrupt the boot process as u-boot\verb0_0reflash indicated we -%% should. We suspect this is a misconfiguration of our serial console, but it's -%% unclear exactly how it is misconfigured, as we were able to receive data fine -%% (we just couldn't send data to the router). -%% * As a result, we were unable to complete the U-Boot installation test. We did -%% appreciate that installation instructions were included, though these -%% instructions should be updated to include more specifics about connecting the -%% serial cable. Since ThinkPenguin does have the option to ship a serial -%% adapter with the router, it would be helpful if instructions specific to that -%% adapter were included, as the wiring configuration one should use was unclear. -%% * Additionally, instructions for removing the router's case should be included. -%% We found that the two screws that needed removal to open the case were hidden -%% underneath rubber feet on the case. Indicating which feet need removal to -%% unscrew the case would be helpful. The instructions should also note that the -%% case needs to be carefully separated once the screws are removed; it -%% effectively snaps apart, but care must be taken to avoid breaking the plastic -%% fasteners that keep the case together after the screws are removed. +\section{U-Boot Installation} + +The U-Boot installation process is substantially more complicated than the +firmware update. The investigator purchased the optional serial cable +along with the TPE-NWIFIROUTER, in order to complete the U-Boot installation +per the instructions in ``u-boot\verb0_0reflash''. + +However, the investigator was only able to read data from the serial port; the +investigator was unable to send key events via the serial port so the U-Boot +console could not be accessed in that way. The investigator did find another +way of accessing the U-Boot console, though, which was used to complete the +U-Boot installation and verification. The likely issue with the serial port was +initial mis-wiring of the serial connector, causing the receive pin to be +permanently disabled. Here are the steps the investigator tried, including the +alternate method of installation that did not require the serial console: + +\begin{itemize} + +\item The investigator found the serial cable included was a USB serial adapter +that had a male USB type A connector on one end and 4 female jumper wires at the +other end. These female jumper wires were red, black, white, and green. + +\item The instructions did not specify how to connect these wires, but the +investigator was able to determine this in part using the "v8.4" image (close to +the "v8.2" version string the investigator found on the bottom of the router) at +\url{http://wiki.openwrt.org/toh/tp-link/tl-wr841nd#serial.console} . Aside +from power and ground (red and black), the investigator did have to guess which +of the wires was RX and TX. By experimentation the investigator found that +green was RX and white was TX. When the investigator tried the other way, no +data was received to the serial console at boot time. While determining which +wires connected to which pins, the investigator may have connected the power pin +to the RX pin; this could explain why the receive (RX) pin later failed to work. + +\item The investigator did have to use the included jumper pin gender changer +with the USB serial adapter, which the investigator put through the holes on the +router's mainboard and then connected to the USB serial adapter. The fit was +fairly loose so it would be nice if future router versions included a tighter +gender changer or (ideally) had the jumper pins soldered onto the board to begin +with (so no gender changer would be required). Since the serial cable is not +strictly required for U-Boot installation (see below), this may not be issue. + +\item The investigator used 115200 8N1 as the serial console setting (with no +hardware or software flow control). This was tested with both the +\verb0minicom0 and \verb0screen0 commands. The investigator found that if all 4 +wires were connected on the USB serial adapter that the router would start +without additional power and the console would receive the startup messages. +The investigator could replicate the same behavior by omitting the power cable +from the USB serial adapter (red wire) and connecting the main power adapter to +the router instead. + +\item While the investigator did see the U-Boot and kernel boot logs in the +serial console, the investigator was unable to interrupt the boot process as +u-boot\verb0_0reflash indicated one should. This is likely related to the +accidental connection of power to the RX pin mentioned earlier, which may have +disabled the pin, preventing the serial port on the router from receiving the +commands sent to it. + +\item The investigator then contacted one of the libreCMC developers to +determine what the serial console issue might be and whether there was an +alternate way to install U-Boot that did not rely on the serial console working. +The developer agreed the the receive pin had likely been disabled so a different +installation method would be needed. The developer indicated that the console +could be accessed via \verb0netcat0 when the router was booted into a special +mode by holding the reset button on the router for 7 seconds after turning on +the router. + +\item The investigator turned on the router while pressing reset as mentioned +above and then ran \verb0nc -u -p 6666 192.168.1.1 66660 on the desktop that was +connected to the router (after changing its IP address to 192.168.1.2). After +pressing Enter, a \verb0uboot>0 prompt appeared and the investigator was able to +confirm the running version by typing \verb0version0 to which the router +responded with "U-Boot 1.1.4 (Jul 28 2014)". + +\item A TFTP server was then setup according to step 1 of the U-Boot +installation steps in u-boot\verb0_0reflash. These instructions did not +explicitly state that the U-Boot image mentioned in step 4 of the build +instructions should be placed in /srv/tftp, but this was evident based on the +instructions that followed. This should be corrected in a future version of +u-boot\verb0_0reflash but, because it was straight-forward based on the context, +did not amount to a compliance issue. + +\item The u-boot\verb0_0reflash steps were then followed starting at step 4, +using the \verb0netcat0 console rather than the serial console (described in +steps 2 and 3). The U-Boot image was downloaded onto the device and then copied +over top of the old U-Boot image. The router was then restarted with the +\verb0reset0 command. + +\item Since the serial cable was still connected, the investigator noticed at +startup that U-Boot now printed "U-Boot 1.1.4 (Oct 17 2014)" as its version +string. This was also confirmed by using the \verb0netcat0 console and the +\verb0version0 command, as was previously done above. The new version string +showed that the router was now running the version of U-Boot that the +investigator built, rather than the one it was shipped with, thus fulfilling the +GPL's requirements that one must be able to build and install the software and +any modified versions. + +\end{itemize} + +While the u-boot\verb0_0reflash instructions appear to be functional for those +able to use a serial console, we would prefer if these instructions were updated +to use the \verb0netcat0 console instead. This provides a number of advantages, +such as no requirement for additional hardware to install a new version of +U-Boot, and less chance of mis-configuring one's serial connector (which would +reduce the risk of damage to the router). The existing instructions appear to +be compliant without modification; this suggestion would merely make it easier +for users to take advantage of the freedoms provided to them by U-Boot and the +rest of the system. \section{Firmware Comparison}