I'm trying to use EasyHook to create connection logger.
I'm declaring connect delegate this way (took from pinvoke.net):
private delegate int ConnectDelegate(IntPtr s, ref sockaddr_in addr, int addrsize);
[DllImport("Ws2_32.dll", SetLastError = true)]
private static extern int connect(IntPtr s, ref sockaddr_in addr, int addrsize);
public struct sockaddr_in
public ushort sin_family;
public ushort sin_port;
public in_addr sin_addr;
[MarshalAs(UnmanagedType.ByValArray, SizeConst = 8)]
public byte sin_zero;
and finally in_addr:
[StructLayout(LayoutKind.Explicit, Size = 4)]
public struct in_addr
[FieldOffset(0)] public byte s_b1;
[FieldOffset(1)] public byte s_b2;
[FieldOffset(2)] public byte s_b3;
[FieldOffset(3)] public byte s_b4;
[FieldOffset(0)] public ushort s_w1;
[FieldOffset(2)] public ushort s_w2;
[FieldOffset(0)] public uint s_addr;
All hooking stuff is just same as in FileMon example. Hooked function looks like this:
private int Connect_Hooked(IntPtr s, ref sockaddr_in addr, int addrsize)
var connectResult = connect(s, ref addr, addrsize);
You may notice this code is not doing anything. So this should work almost same as without any hooks.
But this is not woking :)
variable connectResult here will be -1 (SOCKET_ERROR). Google says i should check GetLastError and WSAGetLastError. I tried both but they give me 0.
I guess there is a problem mapping sockaddr_in struct, but i don't know how to debug it...
Please, tell me what am i doing wrong :)
Thanks in advance.
Jan 11, 2015 at 8:37 PM
Edited Jan 13, 2015 at 12:42 AM
So, i did some research, and it seems like EasyHook is overriding LastError
, so program code always has GetLastError = 0.
Here, i tried to intercept Firefox connections, but it didn't work, so i attached ollydbg to find out whats going on there:
Address Hex dump Command Comments
0F7D11E2 |. 51 PUSH ECX ; /Arg3
0F7D11E3 |. 52 PUSH EDX ; |Arg2
0F7D11E4 |. 56 PUSH ESI ; |Arg1
0F7D11E5 |. FF15 7C738F0F CALL DWORD PTR DS:[<&WSOCK32.#4>] ; \WS2_32.connect <-- here Firefox trying to connect
0F7D11EB |. 894424 0C MOV DWORD PTR SS:[ESP+0C],EAX
0F7D11EF |. 83F8 FF CMP EAX,-1
0F7D11F2 |.- 0F85 82000000 JNE 0F7D127A
0F7D11F8 |. FF15 A8738F0F CALL DWORD PTR DS:[<&WSOCK32.#111>] ; [WS2_32.WSAGetLastError <-- here its looking for error code
Internally, winsock connect function is using SetLastError to set it to WSAEWOULDBLOCK (10035), because the socket was marked as non-blocking. If i dont inject my library with hook, firefox is getting correct error code after calling connect. If i inject my
library, then firefox is always getting 0 from WSAGetLastError (which is just a wrapper for GetLastError).
I rewrote delegate and dllimport declaration, thought it would help, but it didn't...
Here how i have it now:
[UnmanagedFunctionPointer(CallingConvention.StdCall, SetLastError = true)]
private delegate int ConnectDelegate(IntPtr s, IntPtr addr, int addrsize);
[DllImport("Ws2_32.dll", SetLastError = true, CallingConvention = CallingConvention.StdCall)]
private static extern int connect(IntPtr s, IntPtr addr, int addrsize);
private int Connect_Hooked(IntPtr s, IntPtr sockAddrPtr, int addrsize)
return connect(s, sockAddrPtr, addrsize);
Is this behaviour normal for EasyHook?