GetProcessImageFileNameA "Access violation writing location" runtime error - c

Question

I'm using the EnumProcesses function to get all process IDs on the system. Then I iterate over each process ID and pass it to OpenProcess to get a process handle, which I then pass to GetProcessImageFileNameA to get the process name.
Here's a code snippet:
#include <stdio.h>
#include <tchar.h>
#include <Windows.h>
#include <Psapi.h>
DWORD GetProcessName(DWORD processID, TCHAR lpFileName, DWORD nSize)
{
HANDLE hProcess;
DWORD pLength;
// Get process handle
hProcess = OpenProcess(
PROCESS_VM_READ | PROCESS_QUERY_INFORMATION,
FALSE,
processID
);
if ( !hProcess )
return NULL;
// Write process name to buffer
if ( pLength = GetProcessImageFileNameA(hProcess, lpFileName, nSize) )
{
CloseHandle(hProcess);
return pLength;
}
CloseHandle(hProcess);
}
int main(void)
{
DWORD processIDs[PROC_ID_SIZE], cbNeeded, cProcess;
unsigned int i;
// Get process IDs
if ( !EnumProcesses(processIDs, sizeof(processIDs), &cbNeeded) )
return 1;
// Get process ID count
cProcess = cbNeeded / sizeof(DWORD);
printf("Number of Processes: %u | Size of Process Array: %d\n", cProcess, (int)sizeof(processIDs));
// Get the process name of each process
for (i = 0; i < cProcess; i++)
{
if ( processIDs[i] != 0 )
{
// The access violation is happening here
TCHAR processName[MAX_PATH];
GetProcessName(processIDs[i], processName, sizeof(processName));
printf("Process name: %s\n", (char*)processName);
}
}
return 0;
}
It compiles fine, but I get this runtime error:
Exception thrown at 0x00007FF985433338 (KernelBase.dll) in QuickSave.exe: 0xC0000005: Access violation writing location 0x000000000000F8D0.
I have a suspicion it's because I'm declaring processName from outside of the function's scope. When I create another function and declare processName within that function's scope, it works. I'm not entirely sure why.
DWORD PrintProcessName(DWORD processID)
{
HANDLE hProcess;
TCHAR processName[MAX_PATH];
DWORD pLength;
// Get process handle
hProcess = OpenProcess(
PROCESS_VM_READ | PROCESS_QUERY_INFORMATION,
FALSE,
processID
);
if (!hProcess)
return NULL;
// Write process name to buffer and print it
if ( pLength = GetProcessImageFileNameA(hProcess, processName, sizeof(processName)) )
{
printf("Process name: %s\n", (char*)processName);
return pLength;
}
CloseHandle(hProcess);
}
I'm still learning C so I'm probably making a newbie mistake, but hopefully someone can help me make sense of what's going on here.

Answer 1

I have fixed your code. The main errors was bad declaration of GetProcessName, wrong size passed for processName size, incorrect printf format specification, function doesn't always return a value, missing error checks.
#include <stdio.h>
#include <tchar.h>
#include <Windows.h>
#include <Psapi.h>
#define PROC_ID_SIZE 1000
DWORD GetProcessName(DWORD processID, TCHAR *lpFileName, DWORD nSize)
{
HANDLE hProcess;
DWORD pLength;
// Get process handle
hProcess = OpenProcess(
PROCESS_QUERY_LIMITED_INFORMATION,
FALSE,
processID
);
if (!hProcess)
return 0;
// Write process name to buffer
pLength = GetProcessImageFileNameW(hProcess, lpFileName, nSize);
CloseHandle(hProcess);
return pLength;
}
int main(void)
{
DWORD processIDs[PROC_ID_SIZE], cbNeeded, cProcess;
unsigned int i;
// Get process IDs
if (!EnumProcesses(processIDs, sizeof(processIDs), &cbNeeded))
return 1;
// Get process ID count
cProcess = cbNeeded / sizeof(DWORD);
printf("Number of Processes: %u | Size of Process Array: %d\n", cProcess, (int)sizeof(processIDs));
// Get the process name of each process
for (i = 0; i < cProcess; i++)
{
if (processIDs[i] != 0)
{
// The access violation is happening here
TCHAR processName[MAX_PATH];
if (GetProcessName(processIDs[i], processName, sizeof(processName)/sizeof(processName[0])))
printf("Process name: %ls\n", processName);
}
}
return 0;
}