How to programatically read native DLL imports in C#?
- by Eric
The large hunk of C# code below is intended to print the imports of a native DLL. I copied it from from this link and modified it very slightly, just to use LoadLibraryEx as Mike Woodring does here.
I find that when I call the Foo.Test method with the original example's target, MSCOREE.DLL, it prints all the imports fine. But when I use other dlls like GDI32.DLL or WSOCK32.DLL the imports do not get printed. What's missing from this code that would let it print all the imports as, for example, DUMPBIN.EXE does?
(Is there a hint I'm not grokking in the original comment that says, "using mscoree.dll as an example as it doesnt export any thing"?)
Here's the extract that just shows how it's being invoked:
public static void Test()
{
// WORKS:
var path = @"c:\windows\system32\mscoree.dll";
// NO ERRORS, BUT NO IMPORTS PRINTED EITHER:
//var path = @"c:\windows\system32\gdi32.dll";
//var path = @"c:\windows\system32\wsock32.dll";
var hLib = LoadLibraryEx(path, 0,
DONT_RESOLVE_DLL_REFERENCES | LOAD_IGNORE_CODE_AUTHZ_LEVEL);
TestImports(hLib, true);
}
And here is the whole code example:
namespace PETest2
{
[StructLayout(LayoutKind.Explicit)]
public unsafe struct IMAGE_IMPORT_BY_NAME
{
[FieldOffset(0)]
public ushort Hint;
[FieldOffset(2)]
public fixed char Name[1];
}
[StructLayout(LayoutKind.Explicit)]
public struct IMAGE_IMPORT_DESCRIPTOR
{
#region union
/// <summary>
/// CSharp doesnt really support unions, but they can be emulated by a field offset 0
/// </summary>
[FieldOffset(0)]
public uint Characteristics; // 0 for terminating null import descriptor
[FieldOffset(0)]
public uint OriginalFirstThunk; // RVA to original unbound IAT (PIMAGE_THUNK_DATA)
#endregion
[FieldOffset(4)]
public uint TimeDateStamp;
[FieldOffset(8)]
public uint ForwarderChain;
[FieldOffset(12)]
public uint Name;
[FieldOffset(16)]
public uint FirstThunk;
}
[StructLayout(LayoutKind.Explicit)]
public struct THUNK_DATA
{
[FieldOffset(0)]
public uint ForwarderString; // PBYTE
[FieldOffset(4)]
public uint Function; // PDWORD
[FieldOffset(8)]
public uint Ordinal;
[FieldOffset(12)]
public uint AddressOfData; // PIMAGE_IMPORT_BY_NAME
}
public unsafe class Interop
{
#region Public Constants
public static readonly ushort IMAGE_DIRECTORY_ENTRY_IMPORT = 1;
#endregion
#region Private Constants
#region CallingConvention CALLING_CONVENTION
/// <summary>
/// Specifies the calling convention.
/// </summary>
/// <remarks>
/// Specifies <see cref="CallingConvention.Winapi" /> for Windows to
/// indicate that the default should be used.
/// </remarks>
private const CallingConvention CALLING_CONVENTION = CallingConvention.Winapi;
#endregion CallingConvention CALLING_CONVENTION
#region IMPORT DLL FUNCTIONS
private const string KERNEL_DLL = "kernel32";
private const string DBGHELP_DLL = "Dbghelp";
#endregion
#endregion Private Constants
[DllImport(KERNEL_DLL, CallingConvention = CALLING_CONVENTION, EntryPoint = "GetModuleHandleA"), SuppressUnmanagedCodeSecurity]
public static extern void* GetModuleHandleA(/*IN*/ char* lpModuleName);
[DllImport(KERNEL_DLL, CallingConvention = CALLING_CONVENTION, EntryPoint = "GetModuleHandleW"), SuppressUnmanagedCodeSecurity]
public static extern void* GetModuleHandleW(/*IN*/ char* lpModuleName);
[DllImport(KERNEL_DLL, CallingConvention = CALLING_CONVENTION, EntryPoint = "IsBadReadPtr"), SuppressUnmanagedCodeSecurity]
public static extern bool IsBadReadPtr(void* lpBase, uint ucb);
[DllImport(DBGHELP_DLL, CallingConvention = CALLING_CONVENTION, EntryPoint = "ImageDirectoryEntryToData"), SuppressUnmanagedCodeSecurity]
public static extern void* ImageDirectoryEntryToData(void* Base, bool MappedAsImage, ushort DirectoryEntry, out uint Size);
}
static class Foo
{
// From winbase.h in the Win32 platform SDK.
//
const uint DONT_RESOLVE_DLL_REFERENCES = 0x00000001;
const uint LOAD_IGNORE_CODE_AUTHZ_LEVEL = 0x00000010;
[DllImport("kernel32.dll"), SuppressUnmanagedCodeSecurity]
static extern uint LoadLibraryEx(string fileName, uint notUsedMustBeZero, uint flags);
public static void Test()
{
//var path = @"c:\windows\system32\mscoree.dll";
//var path = @"c:\windows\system32\gdi32.dll";
var path = @"c:\windows\system32\wsock32.dll";
var hLib = LoadLibraryEx(path, 0,
DONT_RESOLVE_DLL_REFERENCES | LOAD_IGNORE_CODE_AUTHZ_LEVEL);
TestImports(hLib, true);
}
// using mscoree.dll as an example as it doesnt export any thing
// so nothing shows up if you use your own module.
// and the only none delayload in mscoree.dll is the Kernel32.dll
private static void TestImports( uint hLib, bool mappedAsImage )
{
unsafe
{
//fixed (char* pszModule = "mscoree.dll")
{
//void* hMod = Interop.GetModuleHandleW(pszModule);
void* hMod = (void*)hLib;
uint size = 0;
uint BaseAddress = (uint)hMod;
if (hMod != null)
{
Console.WriteLine("Got handle");
IMAGE_IMPORT_DESCRIPTOR* pIID = (IMAGE_IMPORT_DESCRIPTOR*)Interop.ImageDirectoryEntryToData((void*)hMod, mappedAsImage, Interop.IMAGE_DIRECTORY_ENTRY_IMPORT, out size);
if (pIID != null)
{
Console.WriteLine("Got Image Import Descriptor");
while (!Interop.IsBadReadPtr((void*)pIID->OriginalFirstThunk, (uint)size))
{
try
{
char* szName = (char*)(BaseAddress + pIID->Name);
string name = Marshal.PtrToStringAnsi((IntPtr)szName);
Console.WriteLine("pIID->Name = {0} BaseAddress - {1}", name, (uint)BaseAddress);
THUNK_DATA* pThunkOrg = (THUNK_DATA*)(BaseAddress + pIID->OriginalFirstThunk);
while (!Interop.IsBadReadPtr((void*)pThunkOrg->AddressOfData, 4U))
{
char* szImportName;
uint Ord;
if ((pThunkOrg->Ordinal & 0x80000000) > 0)
{
Ord = pThunkOrg->Ordinal & 0xffff;
Console.WriteLine("imports ({0}).Ordinal{1} - Address: {2}", name, Ord, pThunkOrg->Function);
}
else
{
IMAGE_IMPORT_BY_NAME* pIBN = (IMAGE_IMPORT_BY_NAME*)(BaseAddress + pThunkOrg->AddressOfData);
if (!Interop.IsBadReadPtr((void*)pIBN, (uint)sizeof(IMAGE_IMPORT_BY_NAME)))
{
Ord = pIBN->Hint;
szImportName = (char*)pIBN->Name;
string sImportName = Marshal.PtrToStringAnsi((IntPtr)szImportName); // yes i know i am a lazy ass
Console.WriteLine("imports ({0}).{1}@{2} - Address: {3}", name, sImportName, Ord, pThunkOrg->Function);
}
else
{
Console.WriteLine("Bad ReadPtr Detected or EOF on Imports");
break;
}
}
pThunkOrg++;
}
}
catch (AccessViolationException e)
{
Console.WriteLine("An Access violation occured\n" +
"this seems to suggest the end of the imports section\n");
Console.WriteLine(e);
}
pIID++;
}
}
}
}
}
Console.WriteLine("Press Any Key To Continue......");
Console.ReadKey();
}
}
