path: root/winsup/cygwin/hookapi.cc

/* hookapi.cc

   Copyright 2005, 2006, 2007, 2008 Red Hat, Inc.

This file is part of Cygwin.

This software is a copyrighted work licensed under the terms of the
Cygwin license.  Please consult the file "CYGWIN_LICENSE" for
details. */

#include "winsup.h"
#include <stdlib.h>
#include "ntdll.h"
#include "cygerrno.h"
#include "security.h"
#include "path.h"
#include "fhandler.h"
#include "dtable.h"
#include "cygheap.h"

#define rva(coerce, base, addr) (coerce) ((char *) (base) + (addr))
#define rvacyg(coerce, addr) rva (coerce, cygwin_hmodule, addr)

struct function_hook
{
  const char *name;	// Function name, e.g. "DirectDrawCreateEx".
  const void *hookfn;	// Address of your function.
  void *origfn;		// Stored by HookAPICalls, the address of the original function.
};

/* Given an HMODULE, returns a pointer to the PE header */
static PIMAGE_NT_HEADERS
PEHeaderFromHModule (HMODULE hModule)
{
  PIMAGE_NT_HEADERS pNTHeader;

  if (PIMAGE_DOS_HEADER(hModule) ->e_magic != IMAGE_DOS_SIGNATURE)
    pNTHeader = NULL;
  else
    {
      pNTHeader = PIMAGE_NT_HEADERS (PBYTE (hModule)
				     + PIMAGE_DOS_HEADER (hModule) ->e_lfanew);
      if (pNTHeader->Signature != IMAGE_NT_SIGNATURE)
	pNTHeader = NULL;
    }

  return pNTHeader;
}

static long
rvadelta (PIMAGE_NT_HEADERS pnt, DWORD import_rva)
{
  PIMAGE_SECTION_HEADER section = (PIMAGE_SECTION_HEADER) (pnt + 1);
  for (int i = 0; i < pnt->FileHeader.NumberOfSections; i++)
    if (section[i].VirtualAddress <= import_rva
	&& (section[i].VirtualAddress + section[i].Misc.VirtualSize) > import_rva)
    // if (ascii_strncasematch ((char *) section[i].Name, ".idata", IMAGE_SIZEOF_SHORT_NAME))
      return section[i].VirtualAddress - section[i].PointerToRawData;
  return -1;
}

static void *
putmem (PIMAGE_THUNK_DATA pi, const void *hookfn)
{
  DWORD ofl;
  if (!VirtualProtect (pi, sizeof (PVOID), PAGE_READWRITE, &ofl) )
    return NULL;

  void *origfn = (void *) pi->u1.Function;
  pi->u1.Function = (DWORD) hookfn;

  VirtualProtect (pi, sizeof (PVOID), ofl, &ofl);
  return origfn;
}

/* Builds stubs for and redirects the IAT for one DLL (pImportDesc) */

static bool
RedirectIAT (function_hook& fh, PIMAGE_IMPORT_DESCRIPTOR pImportDesc,
	     HMODULE hm)
{
  // If no import names table, we can't redirect this, so bail
  if (pImportDesc->OriginalFirstThunk == 0)
      return false;

  /* import address table */
  PIMAGE_THUNK_DATA pt = rva (PIMAGE_THUNK_DATA, hm, pImportDesc->FirstThunk);
  /* import names table */
  PIMAGE_THUNK_DATA pn = rva (PIMAGE_THUNK_DATA, hm, pImportDesc->OriginalFirstThunk);

  /* Scan through the IAT, completing the stubs and redirecting the IAT
     entries to point to the stubs. */
  for (PIMAGE_THUNK_DATA pi = pt; pn->u1.Ordinal; pi++, pn++)
    {
      if (IMAGE_SNAP_BY_ORDINAL (pn->u1.Ordinal) )
	continue;

      /* import by name */
      PIMAGE_IMPORT_BY_NAME pimp = rva (PIMAGE_IMPORT_BY_NAME, hm, pn->u1.AddressOfData);

      if (strcmp (fh.name, (char *) pimp->Name) == 0)
	{
	  fh.origfn = putmem (pi, fh.hookfn);
	  if (!fh.origfn)
	    return false;
	  hook_chain *hc;
	  for (hc = &cygheap->hooks; hc->next; hc = hc->next)
	    continue;
	  hc->next = (hook_chain *) cmalloc_abort (HEAP_1_HOOK, sizeof (hook_chain));
	  hc->next->loc = (void **) pi;
	  hc->next->func = fh.hookfn;
	  hc->next->next = NULL;
	  break;
      }
  }

  return true;
}

static void
get_export (function_hook& fh)
{
  PIMAGE_DOS_HEADER pdh = (PIMAGE_DOS_HEADER) cygwin_hmodule;
  if (pdh->e_magic != IMAGE_DOS_SIGNATURE)
    return;
  PIMAGE_NT_HEADERS pnt = (PIMAGE_NT_HEADERS) ((char *) pdh + pdh->e_lfanew);
  if (pnt->Signature != IMAGE_NT_SIGNATURE || pnt->FileHeader.SizeOfOptionalHeader == 0)
    return;
  PIMAGE_EXPORT_DIRECTORY pexp =
    rvacyg (PIMAGE_EXPORT_DIRECTORY,
	 pnt->OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_EXPORT].VirtualAddress);
  if (!pexp)
    return;

  PDWORD pfuncs = rvacyg (PDWORD, pexp->AddressOfFunctions);
  PDWORD pnames = rvacyg (PDWORD, pexp->AddressOfNames);
  for (DWORD i = 0; i < pexp->NumberOfNames; i++)
    if (strcmp (fh.name, rvacyg (char *, pnames[i])) == 0)
      {
	fh.origfn = rvacyg (void *, pfuncs[i]);
	break;
      }
}

static const char *
makename (const char *name, char *&buf, int& i, int inc)
{
  i += inc;
  static const char *testers[] = {"NOTUSED", "64", "32"};
  if (i < 0 || i >= (int) (sizeof (testers) / sizeof (testers[0])))
    return NULL;
  if (i)
    {
      __small_sprintf (buf, "_%s%s", name, testers[i]);
      name = buf;
    }
  return name;
}

/* Find first missing dll in a given executable.
   FIXME: This is not foolproof since it doesn't look for dlls in the
   same directory as the given executable, like Windows.  Instead it
   searches for dlls in the context of the current executable.  */
const char *
find_first_notloaded_dll (path_conv& pc)
{
  const char *res = "?";
  HANDLE hc = NULL;
  HMODULE hm = NULL;
  OBJECT_ATTRIBUTES attr;
  IO_STATUS_BLOCK io;
  HANDLE h;
  NTSTATUS status;

  status = NtOpenFile (&h, SYNCHRONIZE | GENERIC_READ,
		       pc.get_object_attr (attr, sec_none_nih),
		       &io, FILE_SHARE_READ | FILE_SHARE_WRITE,
		       FILE_SYNCHRONOUS_IO_NONALERT
		       | FILE_OPEN_FOR_BACKUP_INTENT
		       | FILE_NON_DIRECTORY_FILE);
  if (!NT_SUCCESS (status))
    goto out;

  hc = CreateFileMapping (h, &sec_none_nih, PAGE_READONLY, 0, 0, NULL);
  NtClose (h);
  if (!hc)
    goto out;
  hm = (HMODULE) MapViewOfFile(hc, FILE_MAP_READ, 0, 0, 0);
  CloseHandle (hc);

  PIMAGE_NT_HEADERS pExeNTHdr;
  pExeNTHdr = PEHeaderFromHModule (hm);

  if (pExeNTHdr)
    {
      DWORD importRVA;
      importRVA = pExeNTHdr->OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_IMPORT].VirtualAddress;
      if (importRVA)
	{
	  long delta = rvadelta (pExeNTHdr, importRVA);

	  // Convert imports RVA to a usable pointer
	  PIMAGE_IMPORT_DESCRIPTOR pdfirst;
	  pdfirst = rva (PIMAGE_IMPORT_DESCRIPTOR, hm, importRVA - delta);

	  // Iterate through each import descriptor, and redirect if appropriate
	  for (PIMAGE_IMPORT_DESCRIPTOR pd = pdfirst; pd->FirstThunk; pd++)
	    {
	      const char *lib = rva (PSTR, hm, pd->Name - delta);
	      if (!LoadLibraryEx (lib, NULL, DONT_RESOLVE_DLL_REFERENCES
					     | LOAD_LIBRARY_AS_DATAFILE))
		{
		  static char buf[NT_MAX_PATH];
		  res = strcpy (buf, lib);
		}
	    }
	}
    }

out:
  if (hm)
    UnmapViewOfFile (hm);

  return res;
}

// Top level routine to find the EXE's imports and redirect them
void *
hook_or_detect_cygwin (const char *name, const void *fn, WORD& subsys)
{
  HMODULE hm = fn ? GetModuleHandle (NULL) : (HMODULE) name;
  PIMAGE_NT_HEADERS pExeNTHdr = PEHeaderFromHModule (hm);

  if (!pExeNTHdr)
    return false;

  subsys =  pExeNTHdr->OptionalHeader.Subsystem;

  DWORD importRVA = pExeNTHdr->OptionalHeader.DataDirectory
		      [IMAGE_DIRECTORY_ENTRY_IMPORT].VirtualAddress;
  if (!importRVA)
    return false;

  long delta = fn ? 0 : rvadelta (pExeNTHdr, importRVA);
  if (delta < 0)
    return false;

  // Convert imports RVA to a usable pointer
  PIMAGE_IMPORT_DESCRIPTOR pdfirst = rva (PIMAGE_IMPORT_DESCRIPTOR, hm, importRVA - delta);

  function_hook fh;
  fh.origfn = NULL;
  fh.hookfn = fn;
  char *buf = (char *) alloca (strlen (name) + sizeof ("_64"));
  int i;
  // Iterate through each import descriptor, and redirect if appropriate
  for (PIMAGE_IMPORT_DESCRIPTOR pd = pdfirst; pd->FirstThunk; pd++)
    {
      if (!ascii_strcasematch (rva (PSTR, hm, pd->Name - delta), "cygwin1.dll"))
	continue;
      if (!fn)
	return (void *) "found it";	// just checking if executable used cygwin1.dll
      i = -1;
      while (!fh.origfn && (fh.name = makename (name, buf, i, 1)))
	RedirectIAT (fh, pd, hm);
      if (fh.origfn)
	break;
    }

  while (!fh.origfn && (fh.name = makename (name, buf, i, -1)))
    get_export (fh);

  return fh.origfn;
}

void
ld_preload ()
{
  char *p = getenv ("LD_PRELOAD");
  if (!p)
    return;
  char *s = (char *) alloca (strlen (p) + 1);
  strcpy (s, p);
  char *here = NULL;
  for (p = strtok_r (s, ":\t\n", &here); p; p = strtok_r (NULL, ":\t\n", &here))
    {
      path_conv lib (p);
      WCHAR libname[lib.get_wide_win32_path_len () + 1];
      if (!LoadLibraryW (lib.get_wide_win32_path (libname)))
	{
	  __seterrno ();
	  api_fatal ("error while loading shared libraries: %s: "
		     "cannot open shared object file: %s", p,
		     strerror (get_errno ()));
	}
    }
}

void
fixup_hooks_after_fork ()
{
  for (hook_chain *hc = &cygheap->hooks; (hc = hc->next); )
    putmem ((PIMAGE_THUNK_DATA) hc->loc, hc->func);
}