Jailbreaking my car's navigation system just so I can change the time
A frustrated car owner embarks on an epic reverse engineering quest to jailbreak his Renault's infotainment system, all to accomplish the seemingly simple task of changing the clock after daylight saving time. This captivating tale of vendor lock-in, baffling UX, and clever kernel exploit tactics perfectly illustrates the absurdity of modern embedded systems and the lengths one will go to reclaim control, resonating deeply with HN's love for technical problem-solving against all odds.
The Lowdown
When Daylight Saving Time shifted, the author faced a seemingly trivial problem: updating the clock in his 2014 Renault Latitude. What began as a simple settings adjustment quickly escalated into a deep dive into embedded system reverse engineering, exposing a baffling design choice by TomTom and Renault that rendered basic functions inaccessible without a proprietary SD card.
- The car's head unit, a TomTom Carminat LIVE, required a specific navigation SD card to access the time settings menu, a detail the author initially dismissed.
- This SD card was protected by DRM, validating its unique CID, preventing a simple copy to a blank card or acquisition of a cheap replacement.
- The author attempted to modify the firmware directly and flash it, but signature checks and a lack of access to the
recoverypartition thwarted this approach. - An emulator was built using QEMU to understand the system's behavior, revealing restrictive mount options (
noexec, read-only partitions) and themaster.scriptexecution flow. - Initial attempts to exploit
master.scriptviaSHEXfor arbitrary code execution orLOGfor file writes were blocked bynoexecmounts or limitations on argument passing and data types. - A breakthrough occurred by adapting a Linux kernel exploit technique: overwriting
/proc/sys/kernel/core_patternto point to a custom script on the SD card. - This allowed a small
master.scriptto write|/bin/sh /media/sdcard/payload.shtocore_patternand then trigger a coredump using/bin/dbus-monitor, executing the custom payload. - The
payload.shscript enabled a full eMMC backup, leading to the discovery that time settings were a simple offset in a binary file, which the author successfully changed from 180 to 120 minutes.
Ultimately, the author spent countless hours and utilized advanced hacking techniques to change a single integer value, highlighting the ludicrous over-engineering and deliberate obstacles placed by manufacturers for even the most basic user interactions.
The Gossip
Car Clock Calamities
Many commenters shared their own exasperating experiences with car clocks, particularly surrounding Daylight Saving Time. The consensus was that modern cars, despite advanced technology, often make simple time adjustments overly complicated, sometimes requiring manual intervention or failing to adapt correctly, leading to widespread frustration and sympathy for the author's plight.
Reverse Engineering Reverie
The technical prowess and persistence demonstrated in the article were a major highlight for the HN community. Commenters lauded the author's meticulous reverse engineering, debugging, and clever exploitation, expressing admiration for the detailed write-up and the satisfaction of solving such a convoluted problem.
SD Card Quandaries
Several discussions revolved around the initial decision to decline the navigation SD card and the implications of its DRM. Some wondered why the author didn't simply take the card, even if outdated, while others discussed the broader issue of vendor lock-in and the gray market for CID-burned SD cards, questioning the necessity of such restrictive measures for basic functionality.
Aftermarket Aspirations
A common thread of conversation explored alternative solutions to such car infotainment woes, ranging from replacing the entire head unit with an aftermarket one to the intriguing possibility of running custom firmware or integrating a Raspberry Pi to hijack the display. These discussions pondered the feasibility and benefits of these approaches compared to the arduous hacking process.