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How to Find Bugs in USB Device Drivers

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How to Find Bugs in USB Device Drivers Don’t trust your USB How to find bugs in USB device drivers OpenSource Security Ralf Spenneberg 2 Motivation • compromise systems via USB • find bugs, fix or exploit them :-) ms_s3c Sergej Schumilo - [email protected] 3 BadUSB (2014) Facedancer (2012) USB Fuzzing for the Masses (2011) ms_s3c Sergej Schumilo - [email protected] 4 Impact • CVE-2013-1285 • CVE-2013-1680 ms_s3c Sergej Schumilo - [email protected] 5 Plug and Root? Darrin Barrall and David Dewey 2005 at Black Hat ms_s3c Sergej Schumilo - [email protected] 6 USB in a nutshell driver initialization driver specific function usb-core-driver specific driver subsystems HID SCSI Enumeration r8192u_usb network Endpoint data transfer udlfb framebuffer ms_s3c Sergej Schumilo - [email protected] 7 Enumeration usb core driver specific device driver Vendor: 0x0bb4 (HTC) ! Product: 0x0a09 (PocketPC Sync) ms_s3c Sergej Schumilo - [email protected] 8 vUSBf Framework • usage of QEMU and KVM for virtualization • usage of USB Redirection interface for USB data injection • send usb traffic through TCP, UDP or Unix sockets • wrap usb data into USB Redirection protocol headers • it supports USB 1.0, 1.1, 2.0, 3.0 ms_s3c Sergej Schumilo - [email protected] 9 USB Redirection redirserver redir specific QEMU USB- emulated VM- libusb usb traffic Device HC Kernel 2. Losungsansatz¨ ! Figure 1. Aufbau usbredirserver • provides remote USB-device Die Anforderungen an das Fuzzing-Framework waren Der USB-Traffic wird dabei logisch zwischen libusb und unteranderem die elengante Losung¨ der langsamen • dempart emuliertenof the SPICE Host-Controller suite (HC) ubertragen¨ (Abb.1). Ausfuhrgeschwindigkeit,¨ die Gegebenheit einer hohen Reell werden die Pakete jedoch in Form von USB- Reproduzierbarkeit und die moglichst¨ luckenlosen¨ Pro- Redirection-Paketen gekapselt. Fur¨ den Verbindungsauf- tokollierung des Impacts verschiedenster USB-Payload. bau und die USB-Redirection-Kommunikation ist in diesem Daruber¨ hinaus sollte das Framework moglichst¨ erweiterbar ms_s3cFall die Software ”usbredirserver” undSergej dieSchumilo QEMU - schumilo@fh-muenster eigene .de sein. Die folgenden Losungsans¨ atze¨ ermoglicht¨ erst die Schnittstelle zustandig.¨ Da das USB-Redirection-Protokoll Implementierung eines USB-Fuzzing-Frameworks, welche relativ einfach ist, lasst¨ sich mit geringe Aufwand diese alle von diesen Anforderungen erfullt.¨ Verbindung auch per Man-In-The-Middle abhoren¨ bzw. gezielt verandern.¨ Dies erlaubt bereits USB-Fuzzing 2.1. Host-Virtualisierung ohne grundlegendes Verstandnis¨ des USB-Protokolls. Al- ternativ lasst¨ sich auch ein USB-Gerat¨ mit Hilfe des USB-Redirection-Protokolls emulieren und somit auch Das Framework setzt fur¨ die Realisierung der gegebenen stateful-USB-fuzzing ermoglichen,¨ ohne dafur¨ jedoch ein Anforderungen auf die im Linux-Kernel integrierte Virtual- physikalisch verfugbares¨ und angeschlossenene USB-Gerat¨ isierungsinfrastruktur KVM, um damit die anzugreifenden vorraus zusetzen. Systeme zu virtualisieren. Da KVM nur den Hypervisior darstellt, wird dieser in Kombination mit QEMU, welches Vorteile in der Verwendung des USB-Redirection- dazu dient weitere benotigte¨ Gerate¨ zu emulieren, zu einer Protokoll sind außerdem die fehlende Limitierung der vollstandigen¨ Virtualisierungslosung.¨ Da diese Virtual- verfugbaren¨ Endpoints, sprich es konnten¨ theoretisch alle isierungslosung,¨ im Gegensatz zu anderen kommerziellen 31 Endpoints verwendet werden. Außerdem unterstutzt¨ das Losungen,¨ unter verschiedenen GPL-Versionen lizensiert USB-Redirection-Protokoll auch das USB 3.0 Protokoll. ist, bietet sie uns damit großtm¨ ogliche¨ Flexibilitat¨ in dieser Verwendung und der Erweiterbarkeit. 2.3. Harddrive-Virtualisierung Die Nutzung von QEMU impliziert fur¨ die virtuellen 2.2. USB-Virtualisierung Maschinen die Verwendung von Image-Dateien oder reellen Partitionen, welche fur¨ die Bereitstellung des Spe- Als USB-Schnittstelle wird das sogenannten USB- icherplatzes der virtuellen Festplatten benotigt¨ werden. Redirecton-Protokoll [5] verwendet, welches zum Zeit- Hierzu verwenden wir Image-Files im QCOW2-Format punkt dieses Papers nur in Kombination mit dem QEMU (QEMU Copy-On-Write). Ein Aufbau fur¨ eine virtuelle eigenen Interface nutzbar ist. Das USB-Redirection- Maschine sieht in der trivialsten Form wie folgt aus: Proktoll ermoglicht¨ die Ubertragung¨ von USB-Traffic in QCOW2-Image Form von TCP, UDP oder Unix-Sockets und dient ur- QEMU load (ca. 2GB) + Snapshot sprunglich¨ der Bereitstellung von entfernten USB-Gerate¨ in virtuellen Umgebungen. Figure 2. Trivialer Aufbau f ¨urQEMU Fur¨ die Bereitstellung eines entfernten USB-Gerates,¨ di- ent die Software ”usbredirserver”, welche Teil der USB- Alternativ lasst¨ sich im QCOW2-Image noch ein Snap- Redirection-Suite ist und es erlaubt ein eingestecktes USB- shot hinterlegen, damit beim Laden der VM der gesicherte Gerat¨ im Netzwerk bereit zustellen. Hierfur¨ wird das Zustand sofort wiederhergestellt wird und man sich zum USB-Gerat¨ per libusb auf dem Host-System an eine eige- Beispiel das Hochfahren des Betriebssystem ersparen nen Treiber-Implementierung gebunden und alle Anfragen kann. Das QCOW2-Image wachst¨ in diesem Fall um ca. des Guest-System werden an die Treiber-Implementierung der Große¨ des Arbeitsspeichers, sowie den Festplatten- durch gereicht. Dadurch entsteht eine logische Verbindung Anderungen.¨ zwischen dem Guest-System und dem USB-Gerat.¨ 2 10 QEMU usbredir- interface VM QEMU monitoring console - monitoring process start - load snapshot - recognition for image corruption QEMU- Contoller ms_s3c Sergej Schumilo - [email protected] 11 QEMU USB-Emulator USB-Traffic usbredir- interface VM traffic fuzzing QEMU monitoring console - monitoring process start descriptor fuzzing Fuzzer-Modul - load snapshot - recognition for image corruption Read or generate Device-Descriptor QEMU- Contoller ms_s3c Sergej Schumilo - [email protected] 12 QEMU USB-Emulator USB-Traffic usbredir- VM monitoring interface per serial port traffic fuzzing Monitoring- QEMU monitoring console Modul - monitoring process start descriptor fuzzing Fuzzer-Modul - load snapshot - recognition for image corruption Read or generate Device-Descriptor QEMU- Contoller write to logfile ms_s3c Sergej Schumilo - [email protected] 13 instance #3 instance #2 instance #1 QEMU USB-Emulator USB-Traffic usbredir- VM monitoring interface per serial port traffic fuzzing Monitoring- QEMU monitoring console Modul - monitoring process start descriptorfuzzing Fuzzer-Modul - load snapshot - recognition for image corruption Read or generate Device-Descriptor read testcase QEMU- Contoller write to logfile testcase- pooltestcase- pooltestcase- pool Testcase-Distributor ms_s3c Sergej Schumilo - [email protected] 14 vUSBf reload mode start QEMU load snapshot send payload write impact to logfile ms_s3c Sergej Schumilo - [email protected] 15 vUSBf Non-reload mode start QEMU load snapshot send payload yes no issue write impact to detected? logfile ms_s3c Sergej Schumilo - [email protected] 16 Reproducibility • test cases are related to unique IDs • file export for a sequence of test cases • offers high reproducibility in combination with snapshots ms_s3c Sergej Schumilo - [email protected] 17 vUSBf Performance reload mode non reload mode 0,5 vUSBf (1 process) 0,5 50 vUSBf Multiprocessing 120 150 vUSBf Clustering 320 0 100 200 300 400 tests per seconds ms_s3c Sergej Schumilo - [email protected] 18 vUSBf Performance runtime for 1 million tests: reload mode non reload mode 23d 4h vUSBf (1 process) 23d 4h 5h 30m vUSBf Multiprocessing 2h 18m 1h 48m vUSBf Clustering 51m 0 1,6547619047619 3,30952380952381 ms_s3c Sergej Schumilo - [email protected] 19 Demo ms_s3c Sergej Schumilo - [email protected] 20 Challenges • Linux monitoring is simple! • other OS? • investigation / fixing of bugs • additional specific USB-emulators ms_s3c Sergej Schumilo - [email protected] BUG: Bad rss-counter state mm:ffff880002a13c00 idx:1 val:2 BUG: Bad rss-counter state mm:ffff8800057e4a80 idx:1 val:2 21 BUG: Bad rss-counter state mm:ffff8800057e5180 idx:1 val:2 BUG: Bad rss-counter state mm:ffff8800057e5880 idx:1 val:2 BUG: Bad rss-counter state mm:ffff880006390e00 idx:1 val:2 BUG: Bad rss-counter state mm:ffff880006391500 idx:1 val:2 BUG: Bad rss-counter state mm:ffff880006391c00 idx:1 val:2 BUG: Bad rss-counter state mm:ffff880007d0c700 idx:1 val:2 BUG: unable to handle kernel NULL pointer dereference at 0000000000000002 Conclusion: BUG: unable to handle kernel NULL pointer dereference at 0000000000000003 BUG: unable to handle kernel NULL pointer dereference at 0000000000000004 BUG: unable to handle kernel NULL pointer dereference at 0000000000000008 BUG: unable to handle kernel NULL pointer dereference at 000000000000000f BUG: unable to handle kernel NULL pointer dereference at 0000000000000042 BUG: unable to handle kernel NULL pointer dereference at 0000000000000043 BUG: unable to handle kernel NULL pointer dereference at 0000000000000044 BUG: unable to handle kernel NULL pointer dereference at 0000000000000046 BUG: unable to handle kernel NULL pointer dereference at 0000000000000048 BUG: unable to handle kernel NULL pointer dereference at 0000000000000058 vast amount of bugs :-)! BUG: unable to handle kernel NULL pointer dereference at 0000000000000068 BUG: unable to handle kernel NULL pointer dereference at 0000000000000070 BUG: unable to handle kernel NULL pointer dereference at 0000000000000098 ! BUG: unable to handle kernel
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