I'm trying to pass a handle from process1 to process2 using the DuplicateHandle function. I obtain the handle using the CreateFile function:
HANDLE COMportHandle;
COMportHandle = CreateFile(TEXT("COM5"),
GENERIC_ALL | PROCESS_DUP_HANDLE,
0,
0,
OPEN_EXISTING,FILE_ATTRIBUTE_NORMAL,
0);
In the second process, I first obtain the process ID from process1 through shared memory, and then try to duplicate the handle:
HANDLE pr1handle, CPH, COMportHandle;
pr1handle = OpenProcess(PROCESS_DUP_HANDLE,FALSE,process_id);
if(!DuplicateHandle(pr1handle,COMportHandle,GetCurrentProcess(),&CPH,PROCESS_DUP_HANDLE,FALSE,0))
printf("Error: %d\n",GetLastError());
Then I get the ERROR_INVALID_HANDLE.
The processes are not related, I run the first to open the COM port, and then want to be able to read from it with the second process.
Can somebody tell me where the catch is?
In this code here:
HANDLE pr1handle, CPH, COMportHandle;
pr1handle = OpenProcess(PROCESS_DUP_HANDLE,FALSE,process_id);
if(!DuplicateHandle(pr1handle,COMportHandle,GetCurrentProcess(),&CPH,PROCESS_DUP_HANDLE,FALSE,0))
printf("Error: %d\n",GetLastError());
you introduce a new, uninitialized COMportHandle. So, assuming this is the actual code, I'm not at all surprised COMportHandle is invalid". You will somehow need to get the actual value of COMportHandle from your first process.
Related
I'm using CreateFileA and the first time I call it, it works as expected. But when i call it the second time, it returns handle INVALID_HANDLE_VALUE. What could be the problem? Just for information, I'm calling it every time I need to check if my USB device is connected..
int port = 500;
char port_name [MAX_CAR] = {0};
sprintf_s (port_name, MAX_CAR, "\\\\.\\COM%d", port);
com->id = CreateFileA (port_name,
GENERIC_READ | GENERIC_WRITE,
0,
NULL,
OPEN_EXISTING,
FILE_FLAG_OVERLAPPED,
NULL);
EDIT: I did try to use CloseHandle like CloseHandle(com->id); but it doesn't help.
From the documentation:
When an application is finished using the object handle returned by
CreateFile, use the CloseHandle function to close the handle. This not
only frees up system resources, but can have wider influence on things
like sharing the file or device and committing data to disk. Specifics
are noted within this topic as appropriate.
Use GetLastError to get the error code, and use the FormatMessage to get a human readable error description, or just simply Google the error code.
There are many reasons can cause the same error (CreateFile returns INVALID_HANDLE_VALUE), without the GetLastError, you will very hard to find out what is the real reason.
I am trying to open process duplicate handles and query information from thread handles using GetThreadContext but i get error ERROR_INVALID_HANDLE or ERROR_GEN_FAILURE. Information about this seems very limited....
processHandle = OpenProcess(PROCESS_DUP_HANDLE, FALSE, pid)
DuplicateHandle(processHandle,handle.Handle,GetCurrentProcess(),&dupHandle,0,FALSE,DUPLICATE_SAME_ACCESS);
memset(&ctx,0x00,sizeof(ctx));
GetThreadContext(dupHandle,&ctx);
printf("Error:%x", GetLastError());
Anyone ?
First of all, as suggested above you should be passing thread handle as the argument, and not process handle.
Then, what part of CONTEXT structure you request to be filled by GetThreadContext API? You leave zero there and there should be 1+ flags to indicate data of interest:
CONTEXT ThreadContext = { CONTEXT_CONTROL };
if(GetThreadContext(ThreadHandle, &ThreadContext)) {
// ...
See also code snippet at https://stackoverflow.com/a/199809/868014
GetThreadContext takes a thread handle not a process handle.
Service:
Creates std out,err,in named pipes. Attaches them to a process that it creates.
HANDLE hStdOut = CreateNamedPipe(szStdOutPipeName,
PIPE_ACCESS_DUPLEX,
PIPE_TYPE_BYTE,
1,
100,
100,
15000,
pSa);
yStartupInfo.hStdOutput = hStdOut;
CreateProcessAsUserW( ..., yStartupInfo, ... );
This part works. The created process's output is being redirected into the pipes.
Client:
Connection to named pipe, Successful. Check if there are bytes to read with a peek (at this point bytes are pushed into the pipe!). Then read the bytes from the pipe.
hStdOutPide = CreateFileW(szPipeNameStdOut,
GENERIC_READ|GENERIC_WRITE,
FILE_SHARE_READ|FILE_SHARE_WRITE,
NULL,
OPEN_EXISTING,
0,
NULL );
PeekNamedPipe(hStdOutPide,
szBuffer,
kunBufferSize,
&ulBytesRead,
&ulBytesAvailable,
&ulRemainingBytes);
if( ulBytesAvailable > 0)
ReadFile(hStdOutPide, szBuffer, 1000, &ulBytesRead, NULL)
I have removed the surrounding code that makes sure the handles are valid and the process is running and so on.
The Peek reveals that ulRemainingBytes is ALWAYS 0. Does anyone see where my error could be? I have been trying to get this to work for some time and don't know what the proper flags for anything is anymore. Please ask if you need more information!
Security Attributes in the CreateNamesPipe are generated from a method. It is used in many other places in the code so I do not believe the problem to be there.
Thanks.
PeekNamedPipe() returns a BOOL that should be checked.
If it fails (FALSE or 0), use GetLastError() to figure out the reason.
And before that you should also check the return value of CreateFile() (hStdOutPide) against INVALID_HANDLE_VALUE. If the returned handle is invalid that could well be a reason for PeekNamedPipe() to fail.
All in all you seem to be taking too many (good) results for taken. Don't! Check your return codes and never rely on luck.
Just one more thing: it's possible that the sharing flags are set improperly. Make sure that they don't conflict with what you want to do. Either way, GetLastError() will again tell you about such issue in case CreateFile() failed.
I suspect you are trying to read from the stdout rather than stdin in your child process. But from the limited code I cannot confirm this. Refer to this question for IPC using pipes
How do I take the output of one program and use it as the input of another on C++?
In C++, I have opened a serial port that has a HANDLE. Since the port may close by an external application, how can I verify that the HANDLE is still valid before reading data?
I think it can be done by checking the HANDLE against a suitable API function, but which?
Thank you.
Checking to see whether a handle is "valid" is a mistake. You need to have a better way of dealing with this.
The problem is that once a handle has been closed, the same handle value can be generated by a new open of something different, and your test might say the handle is valid, but you are not operating on the file you think you are.
For example, consider this sequence:
Handle is opened, actual value is 0x1234
Handle is used and the value is passed around
Handle is closed.
Some other part of the program opens a file, gets handle value 0x1234
The original handle value is "checked for validity", and passes.
The handle is used, operating on the wrong file.
So, if it is your process, you need to keep track of which handles are valid and which ones are not. If you got the handle from some other process, it will have been put into your process using DuplicateHandle(). In that case, you should manage the lifetime of the handle and the source process shouldn't do that for you. If your handles are being closed from another process, I assume that you are the one doing that, and you need to deal with the book keeping.
Some WinAPI functions return meaningless ERROR_INVALID_PARAMETER even if valid handles are passed to them, so there is a real use case to check handles for validity.
GetHandleInformation function does the job:
http://msdn.microsoft.com/en-us/library/ms724329%28v=vs.85%29.aspx
as the port may close by a external application
This is not possible, an external application cannot obtain the proper handle value to pass to CloseHandle(). Once you have the port opened, any other process trying to get a handle to the port will get AccessDenied.
That said, there's crapware out there that hacks around this restriction by having secret knowledge of the undocumented kernel structures that stores handles for a process. You are powerless against them, don't make the mistake of taking on this battle by doing the same. You will lose. If a customer complains about this then give them my doctor's advice: "if it hurts then don't do it".
If you are given a HANDLE and simply want to find out whether it is indeed an open file handle, there is the Windows API function GetFileInformationByHandle for that.
Depending on the permissions your handle grants you for the file, you can also try to move the file pointer using SetFilePointer, read some data from it using ReadFile, or perform a null write operation using WriteFile with nNumberOfBytesToWrite set to 0.
Probably you are under windows and using ReadFile to read the data. The only way to check it is trying to read. If the HANDLE is invalid it'll return an error code (use GetLastEror() to see which one it is) which will probably be ERROR_HANDLE_INVALID.
I know that it's a little bit late but I had a similar question to you, how to check if a pipe (a pipe I created using CreateFile) is still open (maybe the other end shut down the connection) and can read, and if it is not, to open it again. I did what #Felix Dombek suggested, and I used the WriteFile to check the connection. If it returned 1 it means the pipe is open, else I opened it using the CreateFile again. This implies that your pipe is duplex. Here's the CreateFile:
hPipe2 = CreateFile(lpszPipename2, GENERIC_READ | GENERIC_WRITE, 0, NULL, OPEN_ALWAYS, FILE_FLAG_WRITE_THROUGH, NULL);
and here is how I checked for the connection:
while(1)
{
bool MessageSent = WriteFile(hPipe2, "Test", 0, &cbWritten, NULL);
if (!(MessageSent))
{
LogsOut("Read pipe has been disconnected");
//Call method to start the pipe again
break;
}
Sleep(200); // I need this because it is a thread
}
This is working just fine for me :)
You can use DuplicateHandle to test handle validity.
First method: You can try to duplicate the handle you want to check on validity. Basically, invalid handles can not be duplicated.
Second method: The DuplicateHandle function does search the Win32 handle descriptor table from beginning for an empty record to reuse it and so assign into it a duplicated handle. You can just test the duplicated handle address value on value greater than yours handle address and if it is greater, then the handle is not treated as invalid and so is not reused. But this method is very specific and limited, and it does only work, when there is no more empty or invalid handle records above the handle value address you want to test.
But all this just said above is valid only if you track all handles creation and duplication on your side.
Examples for Windows 7:
Method #1
// check stdin on validity
HANDLE stdin_handle_dup = INVALID_HANDLE_VALUE;
const bool is_stdin_handle_dup = !!DuplicateHandle(GetCurrentProcess(), GetStdHandle(STD_INPUT_HANDLE), GetCurrentProcess(), &stdin_handle_dup, 0, FALSE, DUPLICATE_SAME_ACCESS);
if (is_stdin_handle_dup && stdin_handle_dup != INVALID_HANDLE_VALUE) {
CloseHandle(stdin_handle_dup);
stdin_handle_dup = INVALID_HANDLE_VALUE;
}
Method #2
// Assume `0x03` address has a valid stdin handle, then the `0x07` address can be tested on validity (in Windows 7 basically stdin=0x03, stdout=0x07, stderr=0x0b).
// So you can duplicate `0x03` to test `0x07`.
bool is_stdout_handle_default_address_valid = false;
HANDLE stdin_handle_dup = INVALID_HANDLE_VALUE;
const bool is_stdin_handle_dup = !!DuplicateHandle(GetCurrentProcess(), (HANDLE)0x03, GetCurrentProcess(), &stdin_handle_dup, 0, FALSE, DUPLICATE_SAME_ACCESS);
if (is_stdin_handle_dup && stdin_handle_dup != INVALID_HANDLE_VALUE) {
if (stdin_handle_dup > (HANDLE)0x07) {
is_stdout_handle_default_address_valid = true; // duplicated into address higher than 0x07, so 0x07 contains a valid handle
}
CloseHandle(stdin_handle_dup);
stdin_handle_dup = INVALID_HANDLE_VALUE;
}
In order to check the handle , first we need to know what is our HANDLE for, (for a File/Port/Window, ...), Then find an appropriate function to check it (thanks #janm for help). Note that the function's duty may be specially for this destination or not. In my case that iv'e opened a Serial port by CreateFile() , i can check the COM status by GetCommState() API function that fills our COM info struct. If the port is not open anymore or inaccessible the function returns 0 and if you call GetLastError() immediately, you`ll get the ERROR_INVALID_HANDLE value. Thanks everyone for helps.
I have a variable of HANDLE type.
First HANDLE variable is a process HANDLE (with name hProcess) that does not have PROCESS_QUERY_INFORMATION access right.
Second variable is a process HANDLE (with name hwndProcess) too that I have opened via OpenProcess function and have PROCESS_QUERY_INFORMATION access right. I am sure both processes should have same handle.
But when i compare them as below, it returns false;
if (hProcess==hwndProcess) {do something}
How shall I do it?
There is not an explicit way to check whether two handles refer to the same process. The only way would be to query the process information and check that, e.g. using GetProcessId on each handle to check the process IDs.
If you don't have the necessary access rights to call the desired query functions then you can try calling DuplicateHandle to get a new handle with more access rights. However, if this fails then you have no way of telling whether the handles are to the same process or not.
hProcess must not hold the ProcessHandle of the Process that will be closed. It can and will most times be NULL. I'm doing something similar to get the PIDs of terminated processes.
if((hProcess == NULL) || (hProcess == GetCurrentProcess())){
pid = GetCurrentProcessId();
} else {
pid = ProcessHandleToId(hProcess);
}
Are your sure, that it's an access rights problem and your function doesn't fail, because the handle is NULL?
The Windows 10 SDK has CompareObjectHandles(HANDLE, HANDLE) which returns TRUE if the handles refer to the same underlying kernel object.
And you don't have to worry about access rights.