path: root/xpcom/build/PoisonIOInterposerMac.cpp

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "PoisonIOInterposer.h"
#include "mach_override.h"

#include "mozilla/ArrayUtils.h"
#include "mozilla/Assertions.h"
#include "mozilla/DebugOnly.h"
#include "mozilla/IOInterposer.h"
#include "mozilla/Mutex.h"
#include "mozilla/ProcessedStack.h"
#include "mozilla/Telemetry.h"
#include "mozilla/UniquePtrExtensions.h"
#include "nsPrintfCString.h"
#include "mozilla/StackWalk.h"
#include "nsTraceRefcnt.h"
#include "plstr.h"
#include "prio.h"

#include <algorithm>
#include <vector>

#include <sys/param.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <sys/uio.h>
#include <aio.h>
#include <dlfcn.h>
#include <fcntl.h>
#include <unistd.h>

#ifdef MOZ_REPLACE_MALLOC
#include "replace_malloc_bridge.h"
#endif

namespace {

using namespace mozilla;

// Bit tracking if poisoned writes are enabled
static bool sIsEnabled = false;

// Check if writes are dirty before reporting IO
static bool sOnlyReportDirtyWrites = false;

// Routines for write validation
bool IsValidWrite(int aFd, const void* aWbuf, size_t aCount);
bool IsIPCWrite(int aFd, const struct stat& aBuf);

/******************************** IO AutoTimer ********************************/

/**
 * RAII class for timing the duration of an I/O call and reporting the result
 * to the IOInterposeObserver API.
 */
class MacIOAutoObservation : public IOInterposeObserver::Observation
{
public:
  MacIOAutoObservation(IOInterposeObserver::Operation aOp, int aFd)
    : IOInterposeObserver::Observation(aOp, sReference, sIsEnabled &&
                                       !IsDebugFile(aFd))
    , mFd(aFd)
    , mHasQueriedFilename(false)
    , mFilename(nullptr)
  {
  }

  MacIOAutoObservation(IOInterposeObserver::Operation aOp, int aFd,
                       const void* aBuf, size_t aCount)
    : IOInterposeObserver::Observation(aOp, sReference, sIsEnabled &&
                                       !IsDebugFile(aFd) &&
                                       IsValidWrite(aFd, aBuf, aCount))
    , mFd(aFd)
    , mHasQueriedFilename(false)
    , mFilename(nullptr)
  {
  }

  // Custom implementation of IOInterposeObserver::Observation::Filename
  const char16_t* Filename() override;

  ~MacIOAutoObservation()
  {
    Report();
    if (mFilename) {
      free(mFilename);
      mFilename = nullptr;
    }
  }

private:
  int                 mFd;
  bool                mHasQueriedFilename;
  char16_t*           mFilename;
  static const char*  sReference;
};

const char* MacIOAutoObservation::sReference = "PoisonIOInterposer";

// Get filename for this observation
const char16_t*
MacIOAutoObservation::Filename()
{
  // If mHasQueriedFilename is true, then we already have it
  if (mHasQueriedFilename) {
    return mFilename;
  }
  char filename[MAXPATHLEN];
  if (fcntl(mFd, F_GETPATH, filename) != -1) {
    mFilename = UTF8ToNewUnicode(nsDependentCString(filename));
  } else {
    mFilename = nullptr;
  }
  mHasQueriedFilename = true;

  // Return filename
  return mFilename;
}

/****************************** Write Validation ******************************/

// We want to detect "actual" writes, not IPC. Some IPC mechanisms are
// implemented with file descriptors, so filter them out.
bool
IsIPCWrite(int aFd, const struct stat& aBuf)
{
  if ((aBuf.st_mode & S_IFMT) == S_IFIFO) {
    return true;
  }

  if ((aBuf.st_mode & S_IFMT) != S_IFSOCK) {
    return false;
  }

  sockaddr_storage address;
  socklen_t len = sizeof(address);
  if (getsockname(aFd, (sockaddr*)&address, &len) != 0) {
    return true; // Ignore the aFd if we can't find what it is.
  }

  return address.ss_family == AF_UNIX;
}

// We want to report actual disk IO not things that don't move bits on the disk
bool
IsValidWrite(int aFd, const void* aWbuf, size_t aCount)
{
  // Ignore writes of zero bytes, Firefox does some during shutdown.
  if (aCount == 0) {
    return false;
  }

  {
    struct stat buf;
    int rv = fstat(aFd, &buf);
    if (rv != 0) {
      return true;
    }

    if (IsIPCWrite(aFd, buf)) {
      return false;
    }
  }

  // For writev we pass a nullptr aWbuf. We should only get here from
  // dbm, and it uses write, so assert that we have aWbuf.
  if (!aWbuf) {
    return true;
  }

  // Break, here if we're allowed to report non-dirty writes
  if (!sOnlyReportDirtyWrites) {
    return true;
  }

  // As a really bad hack, accept writes that don't change the on disk
  // content. This is needed because dbm doesn't keep track of dirty bits
  // and can end up writing the same data to disk twice. Once when the
  // user (nss) asks it to sync and once when closing the database.
  auto wbuf2 = MakeUniqueFallible<char[]>(aCount);
  if (!wbuf2) {
    return true;
  }
  off_t pos = lseek(aFd, 0, SEEK_CUR);
  if (pos == -1) {
    return true;
  }
  ssize_t r = read(aFd, wbuf2.get(), aCount);
  if (r < 0 || (size_t)r != aCount) {
    return true;
  }
  int cmp = memcmp(aWbuf, wbuf2.get(), aCount);
  if (cmp != 0) {
    return true;
  }
  off_t pos2 = lseek(aFd, pos, SEEK_SET);
  if (pos2 != pos) {
    return true;
  }

  // Otherwise this is not a valid write
  return false;
}

/*************************** Function Interception  ***************************/

/** Structure for declaration of function override */
struct FuncData
{
  const char* Name;      // Name of the function for the ones we use dlsym
  const void* Wrapper;   // The function that we will replace 'Function' with
  void* Function;        // The function that will be replaced with 'Wrapper'
  void* Buffer;          // Will point to the jump buffer that lets us call
                         // 'Function' after it has been replaced.
};

// Wrap aio_write. We have not seen it before, so just assert/report it.
typedef ssize_t (*aio_write_t)(struct aiocb* aAioCbp);
ssize_t wrap_aio_write(struct aiocb* aAioCbp);
FuncData aio_write_data = { 0, (void*)wrap_aio_write, (void*)aio_write };
ssize_t
wrap_aio_write(struct aiocb* aAioCbp)
{
  MacIOAutoObservation timer(IOInterposeObserver::OpWrite,
                             aAioCbp->aio_fildes);

  aio_write_t old_write = (aio_write_t)aio_write_data.Buffer;
  return old_write(aAioCbp);
}

// Wrap pwrite-like functions.
// We have not seen them before, so just assert/report it.
typedef ssize_t (*pwrite_t)(int aFd, const void* buf, size_t aNumBytes,
                            off_t aOffset);
template<FuncData& foo>
ssize_t
wrap_pwrite_temp(int aFd, const void* aBuf, size_t aNumBytes, off_t aOffset)
{
  MacIOAutoObservation timer(IOInterposeObserver::OpWrite, aFd);
  pwrite_t old_write = (pwrite_t)foo.Buffer;
  return old_write(aFd, aBuf, aNumBytes, aOffset);
}

// Define a FuncData for a pwrite-like functions.
#define DEFINE_PWRITE_DATA(X, NAME)                                        \
FuncData X ## _data = { NAME, (void*) wrap_pwrite_temp<X ## _data> };      \

// This exists everywhere.
DEFINE_PWRITE_DATA(pwrite, "pwrite")
// These exist on 32 bit OS X
DEFINE_PWRITE_DATA(pwrite_NOCANCEL_UNIX2003, "pwrite$NOCANCEL$UNIX2003");
DEFINE_PWRITE_DATA(pwrite_UNIX2003, "pwrite$UNIX2003");
// This exists on 64 bit OS X
DEFINE_PWRITE_DATA(pwrite_NOCANCEL, "pwrite$NOCANCEL");


typedef ssize_t (*writev_t)(int aFd, const struct iovec* aIov, int aIovCount);
template<FuncData& foo>
ssize_t
wrap_writev_temp(int aFd, const struct iovec* aIov, int aIovCount)
{
  MacIOAutoObservation timer(IOInterposeObserver::OpWrite, aFd, nullptr,
                             aIovCount);
  writev_t old_write = (writev_t)foo.Buffer;
  return old_write(aFd, aIov, aIovCount);
}

// Define a FuncData for a writev-like functions.
#define DEFINE_WRITEV_DATA(X, NAME)                                   \
FuncData X ## _data = { NAME, (void*) wrap_writev_temp<X ## _data> }; \

// This exists everywhere.
DEFINE_WRITEV_DATA(writev, "writev");
// These exist on 32 bit OS X
DEFINE_WRITEV_DATA(writev_NOCANCEL_UNIX2003, "writev$NOCANCEL$UNIX2003");
DEFINE_WRITEV_DATA(writev_UNIX2003, "writev$UNIX2003");
// This exists on 64 bit OS X
DEFINE_WRITEV_DATA(writev_NOCANCEL, "writev$NOCANCEL");

typedef ssize_t (*write_t)(int aFd, const void* aBuf, size_t aCount);
template<FuncData& foo>
ssize_t
wrap_write_temp(int aFd, const void* aBuf, size_t aCount)
{
  MacIOAutoObservation timer(IOInterposeObserver::OpWrite, aFd, aBuf, aCount);
  write_t old_write = (write_t)foo.Buffer;
  return old_write(aFd, aBuf, aCount);
}

// Define a FuncData for a write-like functions.
#define DEFINE_WRITE_DATA(X, NAME)                                   \
FuncData X ## _data = { NAME, (void*) wrap_write_temp<X ## _data> }; \

// This exists everywhere.
DEFINE_WRITE_DATA(write, "write");
// These exist on 32 bit OS X
DEFINE_WRITE_DATA(write_NOCANCEL_UNIX2003, "write$NOCANCEL$UNIX2003");
DEFINE_WRITE_DATA(write_UNIX2003, "write$UNIX2003");
// This exists on 64 bit OS X
DEFINE_WRITE_DATA(write_NOCANCEL, "write$NOCANCEL");

FuncData* Functions[] = {
  &aio_write_data,

  &pwrite_data,
  &pwrite_NOCANCEL_UNIX2003_data,
  &pwrite_UNIX2003_data,
  &pwrite_NOCANCEL_data,

  &write_data,
  &write_NOCANCEL_UNIX2003_data,
  &write_UNIX2003_data,
  &write_NOCANCEL_data,

  &writev_data,
  &writev_NOCANCEL_UNIX2003_data,
  &writev_UNIX2003_data,
  &writev_NOCANCEL_data
};

const int NumFunctions = ArrayLength(Functions);

} // namespace

/******************************** IO Poisoning ********************************/

namespace mozilla {

void
InitPoisonIOInterposer()
{
  // Enable reporting from poisoned write methods
  sIsEnabled = true;

  // Make sure we only poison writes once!
  static bool WritesArePoisoned = false;
  if (WritesArePoisoned) {
    return;
  }
  WritesArePoisoned = true;

  // stdout and stderr are OK.
  MozillaRegisterDebugFD(1);
  MozillaRegisterDebugFD(2);

#ifdef MOZ_REPLACE_MALLOC
  // The contract with InitDebugFd is that the given registry can be used
  // at any moment, so the instance needs to persist longer than the scope
  // of this functions.
  static DebugFdRegistry registry;
  ReplaceMalloc::InitDebugFd(registry);
#endif

  for (int i = 0; i < NumFunctions; ++i) {
    FuncData* d = Functions[i];
    if (!d->Function) {
      d->Function = dlsym(RTLD_DEFAULT, d->Name);
    }
    if (!d->Function) {
      continue;
    }
    DebugOnly<mach_error_t> t = mach_override_ptr(d->Function, d->Wrapper,
                                                  &d->Buffer);
    MOZ_ASSERT(t == err_none);
  }
}

void
OnlyReportDirtyWrites()
{
  sOnlyReportDirtyWrites = true;
}

void
ClearPoisonIOInterposer()
{
  // Not sure how or if we can unpoison the functions. Would be nice, but no
  // worries we won't need to do this anyway.
  sIsEnabled = false;
}

} // namespace mozilla