I was working on a project, which involves the use of forks, and running programs using child processes. One of the programs (myname) involves a command line argument, which prints a name to the screen based on the command line argument. I want a different program (shell) to run myname using a forked child process, but i'm not sure how to get the command line argument if there is no opportunity to write it.
//myname.c takes in an argument and prints it.
int main(int argc, char *argv[])
{
printf(argv[1]);
return 0;
}
// this is currently what i have in shell.c. With this code, the program is forked and ran, but I am unable to include the command line argument in it and the spot is simply blank.
int main()
{
pid_t processID;
processID = fork();
if (processID == 0)
execl("name", "name", NULL);
wait(NULL);
return 0;
}
Output is nothing due to there being no argument. Is the above code right or should I be using some other form of exec() other than execl()?
Related
I have an imbedded Tcl interpreter and want to redirect its stderr and stdout to a console widget in the application.
Using a chan push command for stderr seems to work (not much testing yet), like explained here:
TCL: Redirect output of proc to a file
I could have a file with the required tcl namespace definition, etc, and do a Tcl_Eval to source that script after creating an interp with Tcl_CreateInterp.
Can I do the same thing using Tcl C library calls instead of running the Tcl commands via a Tcl_Eval?
To implement a channel transformation in C, you first have to define a Tcl_ChannelType structure. Such a structure specifies a name for the transformation and pointers to functions for the different operations that may be done on a channel. Next, you implement the functions that perform those operations. The most important ones are inputProc and outputProc. You also have to implement a watchProc. The pointers for other operations can be set to NULL, if you don't need them.
For your example it may look something like:
static const Tcl_ChannelType colorChannelType = {
"color",
TCL_CHANNEL_VERSION_5,
NULL,
ColorTransformInput,
ColorTransformOutput,
NULL, /* seekProc */
NULL, /* setOptionProc */
NULL, /* getOptionProc */
ColorTransformWatch,
NULL, /* getHandleProc */
NULL, /* close2Proc */
NULL, /* blockModeProc */
NULL, /* flushProc */
NULL, /* handlerProc */
NULL, /* wideSeekProc */
NULL,
NULL
};
Then, when you want to push the transformation onto a channel:
chan = Tcl_StackChannel(interp, &colorChannelType, clientData,
Tcl_GetChannelMode(channel), channel);
For a complete example from the Tcl sources, see tclZlib.c
Not really an answer to my question, but maybe it will help someone to see what works by using a Tcl_Eval to show the tcl code that does the redirection.
proc redir_stdout {whichChan args} {
switch -- [lindex $args 0] {
initialize {
return {initialize write finalize}
}
write {
::HT_puts $whichChan [lindex $args 2]
}
finalize {
}
}
}
chan push stderr [list redir_stdout 1]
chan push stdout [list redir_stdout 2]
Both the chan push commands use the same proc, but pass an different identifier (1 or 2) to indicate whether stdout or stderr was the originator of the output.
HT_puts is an extension provided by the C code:
Tcl_CreateObjCommand(interp,"HT_puts",putsCmd,(ClientData) NULL,NULL);
int TclInterp::putsCmd(ClientData ,Tcl_Interp *,int objcnt,Tcl_Obj * CONST *objv)
{
if (objcnt != 3)
return TCL_ERROR;
int length;
int whichChan;
Tcl_GetIntFromObj(interp,objv[1],&whichChan);
//qDebug() << "Channel is $whichChan";
QString out =Tcl_GetStringFromObj(objv[2],&length);
QColor textColor;
if (whichChan==1)
textColor = QColor(Qt::red);
else
textColor = QColor(Qt::white);
console->putData(out.toUtf8(),textColor);
//qDebug() << out;
return TCL_OK;
}
Text forwarded from stderr gets colored red and text from stdout gets colored white.
And, as I mentioned above, each subsequent command that gets executed via Tcl_Eval needs to have the Tcl_Eval return value processed something like this:
if (rtn != TCL_OK)
{
QString output = Tcl_GetVar(interp, "errorInfo", TCL_GLOBAL_ONLY);
console->putData(output.toUtf8(),QColor(Qt::red));
//qDebug("Failed Tcl_Eval: %d \n%s\n", rtn,
}
To get what's normally printed to stderr by tclsh on a TCL_ERROR into the console (instead of the app's stderr).
I was planning to do the equivalent in C to eliminate the need to run Tcl code in the interpreter for the redirect. But, really there's no need for that.
The Tcl_Eval that does the redirection is done right after doing the Tcl_CreateInterp. Any subsequent Tcl_Evals using that interp will have stdout and stderr redirected to my application's console.
Besides, I'm having trouble understanding how to use Tcl_StackChannel and can't find an example I can follow.
Honestly, can't say that I completely understand the Tcl implementation. I made some assumptions on what gets passed to the proc used in the "chan push" command based on the referenced thread.
It looks like the proc is called with the list specified in the chan push command AND an args list. The first element of the args list is a name like "write" or "initialize". The third element looks like the string to be printed.
Still trying to find a definition of what's passed without having to dig into something like namespace ensemble.
So, it's likely that this Tcl code isn't the best implementation but it's working so far (with limited testing).
We have an application that is run with admin privileges, where (apart from other operations that actually require admin privileges) the user can send emails.
Our email system works like this: admin-run application precompiles the email fields and launches (via CreateProcess) our email application that calls the actual email send. If the email is complete and ready it will send it directly, otherwise it will show the Outlook email form to let the user fill the missing fields and send.
Our email application uses TJclEmail to handle email sending and showing Outlook email form. My problem is this: the email application won't show the Outlook email form if Outlook isn't run as administrator, I guess because it's called from the admin-run application so it inherits privileges. Since Outlook is hardly ever run as administrator I'd like to find a way to call CreateProcess with normal user privileges, insted of inheriting admin privileges from its caller.
Is there a way to do so?
Per How can I launch an unelevated process from my elevated process and vice versa?:
Going from an unelevated process to an elevated process is easy. You can run a process with elevation by passing the runas verb to ShellExecute or ShellExecuteEx.
Going the other way is trickier. For one thing, it’s really hard to munge your token to remove the elevation nature properly. And for another thing, even if you could do it, it’s not the right thing to do, because the unelevated user may be different from the elevated user.
...
The solution here is to go back to Explorer and ask Explorer to launch the program for you. Since Explorer is running as the original unelevated user, the program (in this case, the Web browser) will run as Bob. This is also important in the case that the handler for the file you want to open runs as an in-process extension rather than as a separate process, for in that case, the attempt to unelevate would be pointless since no new process was created in the first place. (And if the handler for the file tries to communicate with an existing unelevated copy of itself, things may fail because of UIPI.)
And then the article goes on to show an example that gets the desktop's IShellFolderViewDual interface, and from that an IShellDispatch2 interface, and then calls IShellDispatch2::ShellExecute() to execute the new process as the logged-in user (which is basically the same example provided on MSDN: Execute In Explorer Sample):
#define STRICT
#include <windows.h>
#include <shldisp.h>
#include <shlobj.h>
#include <exdisp.h>
#include <atlbase.h>
#include <stdlib.h>
void FindDesktopFolderView(REFIID riid, void **ppv)
{
CComPtr<IShellWindows> spShellWindows;
spShellWindows.CoCreateInstance(CLSID_ShellWindows);
CComVariant vtLoc(CSIDL_DESKTOP);
CComVariant vtEmpty;
long lhwnd;
CComPtr<IDispatch> spdisp;
spShellWindows->FindWindowSW(
&vtLoc, &vtEmpty,
SWC_DESKTOP, &lhwnd, SWFO_NEEDDISPATCH, &spdisp);
CComPtr<IShellBrowser> spBrowser;
CComQIPtr<IServiceProvider>(spdisp)->
QueryService(SID_STopLevelBrowser,
IID_PPV_ARGS(&spBrowser));
CComPtr<IShellView> spView;
spBrowser->QueryActiveShellView(&spView);
spView->QueryInterface(riid, ppv);
}
void GetDesktopAutomationObject(REFIID riid, void **ppv)
{
CComPtr<IShellView> spsv;
FindDesktopFolderView(IID_PPV_ARGS(&spsv));
CComPtr<IDispatch> spdispView;
spsv->GetItemObject(SVGIO_BACKGROUND, IID_PPV_ARGS(&spdispView));
spdispView->QueryInterface(riid, ppv);
}
void ShellExecuteFromExplorer(
PCWSTR pszFile,
PCWSTR pszParameters = nullptr,
PCWSTR pszDirectory = nullptr,
PCWSTR pszOperation = nullptr,
int nShowCmd = SW_SHOWNORMAL)
{
CComPtr<IShellFolderViewDual> spFolderView;
GetDesktopAutomationObject(IID_PPV_ARGS(&spFolderView));
CComPtr<IDispatch> spdispShell;
spFolderView->get_Application(&spdispShell);
CComQIPtr<IShellDispatch2>(spdispShell)
->ShellExecute(CComBSTR(pszFile),
CComVariant(pszParameters ? pszParameters : L""),
CComVariant(pszDirectory ? pszDirectory : L""),
CComVariant(pszOperation ? pszOperation : L""),
CComVariant(nShowCmd));
}
int __cdecl wmain(int argc, wchar_t **argv)
{
if (argc < 2) return 0;
CCoInitialize init;
ShellExecuteFromExplorer(
argv[1],
argc >= 3 ? argv[2] : L"",
argc >= 4 ? argv[3] : L"",
argc >= 5 ? argv[4] : L"",
argc >= 6 ? _wtoi(argv[5]) : SW_SHOWNORMAL);
return 0;
}
And per How can I launch an unelevated process from my elevated process, redux:
There’s another way which is a bit more direct, but it assumes that the thing you want to do can be done with a direct CreateProcess call. In other words, if you need the system to look up the user’s file associations or default browser, then this technique is not for you.
The idea is to take advantage of PROCESS_CREATE_PROCESS access and the accompanying PROC_THREAD_ATTRIBUTE_PARENT_PROCESS process thread attribute
...
Basically, this lets you tell the CreateProcess function, "Hey, like, um, pretend that other guy over there is creating the process."
And here is the example from that article:
int main(int, char**)
{
HWND hwnd = GetShellWindow();
DWORD pid;
GetWindowThreadProcessId(hwnd, &pid);
HANDLE process =
OpenProcess(PROCESS_CREATE_PROCESS, FALSE, pid);
SIZE_T size;
InitializeProcThreadAttributeList(nullptr, 1, 0, &size);
auto p = (PPROC_THREAD_ATTRIBUTE_LIST)new char[size];
InitializeProcThreadAttributeList(p, 1, 0, &size);
UpdateProcThreadAttribute(p, 0,
PROC_THREAD_ATTRIBUTE_PARENT_PROCESS,
&process, sizeof(process),
nullptr, nullptr);
wchar_t cmd[] = L"C:\\Windows\\System32\\cmd.exe";
STARTUPINFOEX siex = {};
siex.lpAttributeList = p;
siex.StartupInfo.cb = sizeof(siex);
PROCESS_INFORMATION pi;
CreateProcessW(cmd, cmd, nullptr, nullptr, FALSE,
CREATE_NEW_CONSOLE | EXTENDED_STARTUPINFO_PRESENT,
nullptr, nullptr, &siex.StartupInfo, &pi);
CloseHandle(pi.hProcess);
CloseHandle(pi.hThread);
delete[] (char*)p;
CloseHandle(process);
return 0;
}
This program runs a copy of cmd.exe using the shell process (usually explorer.exe) as its parent, which means that if the shell process is unelevated, then so too will the cmd.exe process. Of course, if the user is an administrator and has disabled UAC, then Explorer will still be elevated, and so too will be the cmd.exe. But in that case, the user wants everything to run elevated, so you’re just following the user's preferences.
I am quite new to using pcap lib, so please bear with me.
I am trying to use pcap_getnonblock function, the documentation says the following:
pcap_getnonblock() returns the current 'non-blocking' state of
the capture descriptor; it always returns 0 on 'savefiles' . If
there is an error, PCAP_ERROR is returned and errbuf is filled in
with an appropriate error message.
errbuf is assumed to be able to hold at least PCAP_ERRBUF_SIZE
chars.
I got -3 returned and the errbuf is an empty string, I couldn't understand the meaning of such result.
I believe this caused a socket error: 10065.
This problem happened only once and I could not reproduce it, but still it would be great to find its causing to prevent it in future executions.
Thanks in advance.
pcap_getnonblock() can return -3 - that's PCAP_ERROR_NOT_ACTIVATED. Unfortunately, that's not documented; I'll fix that.
Here's a minimal reproducible example that demonstrates this:
#include <pcap/pcap.h>
#include <stdio.h>
int
main(int argc, char **argv)
{
pcap_t *pcap;
char errbuf[PCAP_ERRBUF_SIZE];
if (argc != 2) {
fprintf(stderr, "Usage: this_program <interface_name>\n");
return 1;
}
pcap = pcap_create(argv[1], errbuf);
if (pcap == NULL) {
fprintf(stderr, "this_program: pcap_create(%s) failed: %s\n",
argv[1], errbuf);
return 2;
}
printf("pcap_getnonblock() returns %d on non-activated pcap_t\n",
pcap_getnonblock(pcap, errbuf));
return 0;
}
(yes, that's minimal, as 1) names of interfaces are OS-dependent, so it has to be a command-line argument and 2) if you don't run the program correctly, it should let you know what's happening, so you know what you have to do in order to reproduce the problem).
Perhaps pcap_getnonblock() and pcap_setnonblock() should be changed so that you can set non-blocking mode before activating the pcap_t, so that, when activated, it will be in non-blocking mode. It doesn't work that way currently, however.
I.e., you're allocating a pcap_t with pcap_create(), but you're not activating it with pcap_activate(). You need to do both in order to have a pcap_t on which you can capture.
In short what I want to do is be able to cause a Data Execution Prevention (DEP) error at will.
This is specifically on XP SP3 machines. I'd like it so that when I run a script or small program it brings up the XP DEP error box.
Would I be right in thinking the simplest way to do that is with some sort of script or program? I know DEP is used to prevent buffer overflow attacks but i'd rather not risk any
malicious code being used.
Can anybody suggest anything to get me on the right lines?
The simplest way is to allocate memory without the executable attribute and jump to the address allocated.
This can be done with the following code.
void Code(){
return;
}
void GenerateDepError(){
// Allocate data area
PVOID pMem = VirtualAlloc( NULL, 0x100,
MEM_COMMIT | MEM_RESERVE, PAGE_READWRITE );
// Copy a function into data area
for( DWORD i = 0; i < 0x100; i++ ){
((char*)pMem)[i] = ((char*)Code)[i];
}
// Consider the memory area as a function.
void (*dep_trigger)() = (void (*)())pMem;
// Invoke the function. This should cause DEP error if DEP is ON.
dep_trigger();
// If it returns without error this message will be displayed.
printf("No error on dep_trigger()\n");
}
int main( int argc, char** argv ){
GenerateDepError();
return 0;
}
I'm trying to write a very simple program to replace an existing executable. It should munge its arguments slightly and exec the original program with the new arguments. It's supposed to be invoked automatically and silently by a third-party library.
It runs fine, but it pops up a console window to show the output of the invoked program. I need that console window to not be there. I do not care about the program's output.
My original attempt was set up as a console application, so I thought I could fix this by writing a new Windows GUI app that did the same thing. But it still pops up the console. I assume that the original command is marked as a console application, and so Windows automatically gives it a console window to run in. I also tried replacing my original call to _exec() with a call to system(), just in case. No help.
Does anyone know how I can make this console window go away?
Here's my code:
int APIENTRY _tWinMain(HINSTANCE hInstance,
HINSTANCE hPrevInstance,
char* lpCmdLine,
int nCmdShow)
{
char *argString, *executable;
// argString and executable are retrieved here
std::vector< std::string > newArgs;
// newArgs gets set up with the intended arguments here
char const ** newArgsP = new char const*[newArgs.size() + 1];
for (unsigned int i = 0; i < newArgs.size(); ++i)
{
newArgsP[i] = newArgs[i].c_str();
}
newArgsP[newArgs.size()] = NULL;
int rv = _execv(executable, newArgsP);
if (rv)
{
return -1;
}
}
Use the CreateProcess function instead of execve. For the dwCreationFlags paramter pass the CREATE_NO_WINDOW flag. You will also need to pass the command line as a string as well.
e.g.
STARTUPINFO startInfo = {0};
PROCESS_INFORMATION procInfo;
TCHAR cmdline[] = _T("\"path\\to\\app.exe\" \"arg1\" \"arg2\"");
startInfo.cb = sizeof(startInfo);
if(CreateProcess(_T("path\\to\\app.exe"), cmdline, NULL, NULL, FALSE, CREATE_NO_WINDOW, NULL, NULL, &startInfo, &procInfo))
{
CloseHandle(procInfo.hProcess);
CloseHandle(procInfo.hThread);
}
Aha, I think I found the answer on MSDN, at least if I'm prepared to use .NET. (I don't think I'm really supposed to, but I'll ignore that for now.)
System::String^ command = gcnew System::String(executable);
System::Diagnostics::Process^ myProcess = gcnew Process;
myProcess->StartInfor->FileName = command;
myProcess->StartInfo->UseShellExecute = false; //1
myProcess->StartInfo->CreateNowindow = true; //2
myProcess->Start();
It's those two lines marked //1 and //2 that are important. Both need to be present.
I really don't understand what's going on here, but it seems to work.
You need to create a non-console application (i.e. a Windows GUI app). If all this app does is some processing of files or whatever, you won't need to have a WinMain, register any windows or have a message loop - just write your code as for a console app. Of course, you won't be able to use printf et al. And when you come to execute it, use the exec() family of functions, not system().