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Can aonone help me to understand this?

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rain-13
Expert Cheater

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Joined: 18 Mar 2009
Posts: 110

Posted: Sat Aug 01, 2015 5:36 am Post subject: Can aonone help me to understand this?

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Hi

I have found pretty interesting thing that I dont understand why it happens. I am trying to hook GetDiskFreeSpaceW with following code.

Code:

BOOL WINAPI DetourGetDiskFreeSpaceW(
_In_ LPCTSTR lpRootPathName,
_Out_ LPDWORD lpSectorsPerCluster,
_Out_ LPDWORD lpBytesPerSector,
_Out_ LPDWORD lpNumberOfFreeClusters,
_Out_ LPDWORD lpTotalNumberOfClusters
){
printf("DetourGetDiskFreeSpaceW\n&lpNumberOfFreeClusters: %llX\n",&lpNumberOfFreeClusters);
//BOOL ret = fpGetDiskFreeSpaceW(lpRootPathName,lpSectorsPerCluster,lpBytesPerSector,lpNumberOfFreeClusters,lpTotalNumberOfClusters);
printf("before cheating %d \n",*lpNumberOfFreeClusters);
(*lpNumberOfFreeClusters) = (DWORD)99999999;
(*lpTotalNumberOfClusters) = (DWORD)999999999;
(*lpBytesPerSector) = (DWORD)65535;
(*lpSectorsPerCluster) = (DWORD)128;
printf("faked space %d \n",lpNumberOfFreeClusters);
return 1;
}

Now, when I try to hook my own program, it works correctly.

But when I hook installer then it crashes.

As it can be seen from screenshots it crashes when printf tries to read the variable.

Code:

printf("before cheating %d \n",*lpNumberOfFreeClusters);

Could anyone help me to understand why this happens and what could fix it?

It looks so strange to me because I dont do anything with variable itself yet. I just try to read it. I dont even try to modify it at first. And even it I do modify it to invalid value, it still shouldn't crash before the caller uses these value, but it crashes when the code execution is still in hook.

I also figured that when I view address that gets printed in CE then with my app it points to address which value contains lpNumberOfFreeClusters's value but with setup if I add this printed address to CE it is 0.

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atom0s
Moderator

Reputation: 205

Joined: 25 Jan 2006
Posts: 8587
Location: 127.0.0.1

Posted: Sat Aug 01, 2015 12:30 pm Post subject:

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You can't write to the following values like you are:

Code:

(*lpNumberOfFreeClusters) = (DWORD)99999999;
(*lpTotalNumberOfClusters) = (DWORD)999999999;
(*lpBytesPerSector) = (DWORD)65535;
(*lpSectorsPerCluster) = (DWORD)128;

I showed you how to use them properly in the other thread.
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rain-13
Expert Cheater

Reputation: 0

Joined: 18 Mar 2009
Posts: 110

Posted: Sat Aug 01, 2015 1:08 pm Post subject:

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Nope, that's the other thing already. In previous thread I played with GetDiskFreeSpaceExW but now I have GetDiskFreeSpaceW.
And in this thread, it crashes already at printf.

Code:

printf("before cheating %d \n",*lpNumberOfFreeClusters);

This line doesnt even get printed anymore (as it can be seen from screenshots). And this line is before code you pointed out.

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