i have been scratching my head and been searching for an answer for this for hours now. Basically what I do is open a socket to some other machine and reading the data from it. This socket is than "converted" to a file handle via an fdopen call passing in the int that represent the socket. The resulting file handle is then passed to a bison parser which directly parsed the data received over the socket. All of this works fine on linux. Now I have tried to port this code to windows and I dismally fail. The code looks something like this:
FILE* fileHandle;
#if defined WINCE || defined WIN32
int fd = _open_osfhandle(socket, _O_RDONLY);
if (fileHandle = fdopen(fd, "r")) {
#else
if (fileHandle = fdopen(socket, "r")) {
#endif
... // code to call my parser with fileHandle as argument
The bison/flex parser fails in the windows version since the filehandle seems to point to an empty stream/file. Can anybody point to a comprehensive resource that explains this stuff or hint at an alternative solution?
Thanks and best Regards,
André
In Windows, a socket handle is not a file handle, and you cannot treat it as such in the C API. In Linux, you can. However, in Windows, a socket handle can be passed to the ReadFile/Ex() and WriteFile/Ex() functions, which support numerous handle types, not just files, despite their names.
You need to fake a little bit, but this one works for me - nSocketFd a file descriptor return by socket()
FILE* fpSocket = NULL;
#ifdef WIN32
fpSocket = new FILE;
fpSocket->_file = nSocketFd;
fpSocket->_cnt = 0;
fpSocket->_ptr = NULL;
fpSocket->_base = NULL;
fpSocket->_flag = 0;
#else
// build the file pointer from the file descriptor
fpSocket = fdopen (nSocketFd, "rb+");
#endif
Related
I'm currently integrating libFuzzer in a project which parses files on the hard drive. I have some prior experience with AFL, where a command line like this one was used:
afl-fuzz -m500 -i input/ -o output/ -t100 -- program_to_fuzz ##
...where ## was a path to the generated input.
Looking at libFuzzer however, I see that the fuzz targets look like this:
extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
DoSomethingInterestingWithMyAPI(Data, Size);
return 0; // Non-zero return values are reserved for future use.
}
I understand that the input isn't provided in the form of a file, but as a buffer in-memory instead. The problem is that the program I'm trying to fuzz works with files and obtains its data through fread() calls. At no point in time is the whole input supposed to be loaded in memory (where, in the general case, it might not even fit); so there's not much I can do with a const uint8_t*.
Writing the buffer back to the hard drive to get back a file seems extremely inefficient. Is there a way around this?
You can do as in this example from google security team.
The buf_to_file defined here takes your buffer and returns a char* pathname you can then pass to you target:
(from https://github.com/google/security-research-pocs/blob/master/autofuzz/fuzz_utils.h#L27 )
// Write the data provided in buf to a new temporary file. This function is
// meant to be called by LLVMFuzzerTestOneInput() for fuzz targets that only
// take file names (and not data) as input.
//
// Return the path of the newly created file or NULL on error. The caller should
// eventually free the returned buffer (see delete_file).
extern "C" char *buf_to_file(const uint8_t *buf, size_t size);
Be sure to free the ressource with the delete_file function.
You could use LD_PRELOAD and override fread.
I have been trying to write a working program that takes in data from a UDP socket and displays it in an edit control box as you receive the data (My exposure to c++ is also only about a week :P have only done embedded C code before). I have a working program that can send and output data on a button click but I want something that can do it in real time. The aim is scale this up into a larger GUI program that can send control data to hardware and get responses from them.
I have run into various problems including:
The program just not executing my OnReceivefunction (derived from
CAsyncSocket)
Getting the OnReceive function to run on a separate thread so that it can still run after a button has been clicked sending a control packet to the client then waiting for a response in a while loop
Not being able to output the data in the edit box (tried using both CEdit and CString)
ReplaceSel error saying that the type char is incompatible with LPCTSTR
My code is based on this codeproject.com tutorial, being almost exactly what I want but I get the error in 4.
EDIT: the error in 4. disappears when I change it to a TCHAR but then it outputs random chinese characters. The codeproject.com tutorial outputs the correct characters regardless of char or TCHAR declaration. When debugged my code has type wchar_t instead type char like the other code.
Chinese output
In the working program echoBuffer[0] the character sent and displayed was a 1
UINT ReceiveData(LPVOID pParam)
{
CTesterDlg *dlg = (CTesterDlg*)pParam;
AfxSocketInit(NULL);
CSocket echoServer;
// Create socket for sending/receiving datagrams
if (echoServer.Create(12345, SOCK_DGRAM, NULL) == 0)
{
AfxMessageBox(_T("Create() failed"));
}
for (;;)
{ // Run forever
// Client address
SOCKADDR_IN echoClntAddr;
// Set the size of the in-out parameter
int clntAddrLen = sizeof(echoClntAddr);
// Buffer for echo string
char echoBuffer[ECHOMAX];
// Block until receive message from a client
int recvMsgSize = echoServer.ReceiveFrom(echoBuffer, ECHOMAX, (SOCKADDR*)&echoClntAddr, &clntAddrLen, 0);
if (recvMsgSize < 0)
{
AfxMessageBox(_T("RecvFrom() failed"));
}
echoBuffer[recvMsgSize] = '\0';
dlg->m_edit.ReplaceSel(echoBuffer);
dlg->m_edit.ReplaceSel(_T("\r\n"));
}
}
After reading the link that #IInspectable provided about working with strings and checking the settings differences between the two programs it became clear that the issue lay with an incorrect conversion to UNICODE. My program does not require it so I disabled it.
This has cleared up the issue in 4. and provided solutions for 2 and 3.
I also think I know why another instance of my program would not run OnReceivein 1. because that file was not being defined by one that was already being run by the program, but that is now irrelevant.
I hooked system calls open, read, write, lstat etc. using osxinj project. Injected this into TextEdit application provided by apple and everything worked fine. When I opened new file using textedit, opencallback was called and messages were logged in system.log file.
typedef int (*open_type)(const char *, int, mode_t);
open_type open_func = 0;
int opencallback(const char* path, int oflag, mode_t mode)
{
syslog(LOG_ALERT, "In open...");
int returnVal = open_func(path, oflag, mode);
syslog(LOG_ALERT,"Open, ends\n");
return returnVal;
}
Injected into Excel and tried to override open system call using below code:
void* func_ptr = dlsym( RTLD_NEXT, "open");
if (func_ptr)
{
open_func = (open_type)func_ptr;
mach_error_t me = mach_override_ptr( func_ptr,
(void*)&opencallback,
(void**)&open_func);
}
opencallback is called when injecting to TextEdit but it is not getting called when injected in Microsoft Excel. But code written on same lines for other system calls read, write, lstat are getting interposed when injected in Excel.
Any thoughts on why open is not getting interposed when injected to Excel.
Finally, I got my code running. I am posting answer hoping it might help somebody.
I hooked __open which is an alias for open and it worked fine for i386 application like excel.
I want to implement the already defined system calls in PintOS ( halt(), create()...etc defined in pintos/src/lib/user/syscall.c ). The current system call handler in pintos/src/userprog/syscall.c does not do anything. How do I make a process that makes system calls. Further I need to myself add a few system calls. How do I proceed in that too. But first I need to implement the existing system calls.
The default implementation in pintos terminates the calling process.
goto this link.There is explanation on where to modify the code to implement the system calls.
The "src/examples" directory contains a few sample user programs.
The "Makefile" in this directory compiles the provided examples, and you can edit it compile your own programs as well.
This program/process when run will inturn make a system call.
Use gdb to follow the execution of one such program a simple printf statement will eventually call write system call to STDOUT file.
The link given also has pointers on how to run pintos on gdb, my guess is you are using either bochs or qemu.In any case just run the gdb once with a simple hello world program running on pintos.
This will give u an idea of how the system call is made.
static void
syscall_handler (struct intr_frame *f)// UNUSED)
{
int *p=f->esp;
switch(*p)
case *p=SYS_CREATE // NUMBER # DEFINED
const char *name=*(p+1); //extract the filename
if(name==NULL||*name==NULL)
exit(-1);
off_t size=(int32_t)*(p+2);//extract file size
f->eax=filesys_create(name,size,_FILE); //call filesys_create
//eax will have the return value
}
This is pseudo code for sys_create .. all file system related system call are very trivial,
Filesys realted system calls like open read write close needs you to translate file to their corresponding fd (file descriptor). You need to add a file table for each process to keep track this, this can either be preprocess data or a global data.(UR choice),
case (*p==SYS_WRITE)
{
// printf("wite syscall\n");
char *buffer=*(p+2);
unsigned size=*(p+3);
int fd=*(p+1);
// getiing the fd of specified file
struct file *fil= thread_current()->fdtable[fd];/ my per thread fdtable
if(fd==1) goto here;
if(is_directory(fil->inode)){
exit(-1);
goto done;
}
here:
if(buffer>=PHYS_BASE)exit(-1);
if(fd<0||fd>=128){exit(-1);}
if(fd==0){exit(-1);} // writing to STDIN
if(fd==1) //writing to STDOUT
{
int a=(int)size;
while(a>=100)
{
putbuf(buffer,100);
buffer=buffer+100;
a-=100;
}
putbuf(buffer,a);
f->eax=(int)size;
}
else
if(thread_current()->fdtable[fd]==NULL)
{f->eax=-1;}
else
{
f->eax=file_write(thread_current()->fdtable[fd],buffer,(off_t)size);
}
done: ;
}//printf("write");} /* Write to a file. */
Open - adds anew entry to fdtable and return the fd number u give to the file,
close - remove that entry from fd table
read - similar to write.
The process_create ,wait are not simple to implement...
Cheers :)
I am writing an UDP client/server programs in C on linux. The thing is that I must add connection check feature. in linux man pages i found example of udp client with this feature( http://www.kernel.org/doc/man-pages/online/pages/man3/getaddrinfo.3.html ). It uses write/read functions to check server response. I tried to apply it to my program, and it looks like this:
char *test = "test";
nlen = strlen(test) + 1;
if (write(sock, test, nlen) != nlen) { // socket with the connection
fprintf(stderr, "partial/failed write\n");
exit(EXIT_FAILURE);
}
nread = read(sock, buf, nlen);
if (nread == -1) {
perror("Connection");
exit(EXIT_FAILURE);
}
the problem is than than i execute program with this bit when server is on, it does nothing except reading input infinite time which it doesn't use too. I tried kill(getpid(), SIGHUP) interrupt, which i found other similar topic here, and shutdown(sock, 1), but nothing seems to work. Could you please tell me a way out how to stop the input read or any other possible option to check if udp server is active?
You should use asynchronous reading.
For this you must use the select() function from "sys/socket.h".
The function monitors the socket descriptor for changes without blocking.
You can find the reference for it here or here or by typing "man select" in your console.
There is an example here for Windows, but its usage is very similar to UNIX.