toolkit/xre/MultiInstanceLock.cpp

   1 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim:set ts=2 sw=2 sts=2 et cindent: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #include "MultiInstanceLock.h"
   8
   9 #include "commonupdatedir.h"  // for GetInstallHash
  10 #include "mozilla/UniquePtr.h"
  11 #include "nsPrintfCString.h"
  12 #include "nsPromiseFlatString.h"
  13 #include "updatedefines.h"  // for NS_t* definitions
  14
  15 #ifdef XP_WIN
  16 #  include <shlwapi.h>
  17 #else
  18 #  include <fcntl.h>
  19 #  include <sys/stat.h>
  20 #  include <sys/types.h>
  21 #endif
  22
  23 #ifdef XP_WIN
  24 #  include "WinUtils.h"
  25 #endif
  26
  27 #ifdef MOZ_WIDGET_COCOA
  28 #  include "nsILocalFileMac.h"
  29 #endif
  30
  31 namespace mozilla {
  32
  33 static bool GetLockFileName(const char* nameToken, const char16_t* installPath,
  34                             nsCString& filePath) {
  35 #ifdef XP_WIN
  36   // On Windows, the lock file is placed at the path
  37   // [updateDirectory]\[nameToken]-[pathHash], so first we need to get the
  38   // update directory path and then append the file name.
  39
  40   // Note: This will return something like
  41   //   C:\ProgramData\Mozilla-1de4eec8-1241-4177-a864-e594e8d1fb38\updates\<hash>
  42   // But we actually are going to want to return the root update directory,
  43   // the grandparent of this directory, which will look something like this:
  44   //   C:\ProgramData\Mozilla-1de4eec8-1241-4177-a864-e594e8d1fb38
  45   mozilla::UniquePtr<wchar_t[]> updateDir;
  46   HRESULT hr = GetCommonUpdateDirectory(
  47       reinterpret_cast<const wchar_t*>(installPath), updateDir);
  48   if (FAILED(hr)) {
  49     return false;
  50   }
  51
  52   // For the path manipulation that we are about to do, it is important that
  53   // the update directory have no trailing slash.
  54   size_t len = wcslen(updateDir.get());
  55   if (len == 0) {
  56     return false;
  57   }
  58   if (updateDir.get()[len - 1] == '/' || updateDir.get()[len - 1] == '\\') {
  59     updateDir.get()[len - 1] = '\0';
  60   }
  61
  62   wchar_t* hashPtr = PathFindFileNameW(updateDir.get());
  63   // PathFindFileNameW returns a pointer to the beginning of the string on
  64   // failure.
  65   if (hashPtr == updateDir.get()) {
  66     return false;
  67   }
  68
  69   // We need to make a copy of the hash before we modify updateDir to get the
  70   // root update dir.
  71   size_t hashSize = wcslen(hashPtr) + 1;
  72   mozilla::UniquePtr<wchar_t[]> hash = mozilla::MakeUnique<wchar_t[]>(hashSize);
  73   errno_t error = wcscpy_s(hash.get(), hashSize, hashPtr);
  74   if (error != 0) {
  75     return false;
  76   }
  77
  78   // Get the root update dir from the update dir.
  79   BOOL success = PathRemoveFileSpecW(updateDir.get());
  80   if (!success) {
  81     return false;
  82   }
  83   success = PathRemoveFileSpecW(updateDir.get());
  84   if (!success) {
  85     return false;
  86   }
  87
  88   filePath =
  89       nsPrintfCString("%s\\%s-%s", NS_ConvertUTF16toUTF8(updateDir.get()).get(),
  90                       nameToken, NS_ConvertUTF16toUTF8(hash.get()).get());
  91
  92 #else
  93   mozilla::UniquePtr<NS_tchar[]> pathHash;
  94   if (!GetInstallHash(installPath, pathHash)) {
  95     return false;
  96   }
  97
  98   // On POSIX platforms the base path is /tmp/[vendor][nameToken]-[pathHash].
  99   filePath = nsPrintfCString("/tmp/%s%s-%s", MOZ_APP_VENDOR, nameToken,
 100                              pathHash.get());
 101
 102 #endif
 103
 104   return true;
 105 }
 106
 107 MultiInstLockHandle OpenMultiInstanceLock(const char* nameToken,
 108                                           const char16_t* installPath) {
 109   nsCString filePath;
 110   if (!GetLockFileName(nameToken, installPath, filePath)) {
 111     return MULTI_INSTANCE_LOCK_HANDLE_ERROR;
 112   }
 113
 114   // Open a file handle with full privileges and sharing, and then attempt to
 115   // take a shared (nonexclusive, read-only) lock on it.
 116 #ifdef XP_WIN
 117   HANDLE h =
 118       ::CreateFileW(PromiseFlatString(NS_ConvertUTF8toUTF16(filePath)).get(),
 119                     GENERIC_READ | GENERIC_WRITE,
 120                     FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE,
 121                     nullptr, OPEN_ALWAYS, 0, nullptr);
 122   if (h != INVALID_HANDLE_VALUE) {
 123     // The LockFileEx functions always require an OVERLAPPED structure even
 124     // though we did not open the lock file for overlapped I/O.
 125     OVERLAPPED o = {0};
 126     if (!::LockFileEx(h, LOCKFILE_FAIL_IMMEDIATELY, 0, 1, 0, &o)) {
 127       CloseHandle(h);
 128       h = INVALID_HANDLE_VALUE;
 129     }
 130   }
 131   return h;
 132
 133 #else
 134   int fd = ::open(PromiseFlatCString(filePath).get(),
 135                   O_CLOEXEC | O_CREAT | O_NOFOLLOW,
 136                   S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH);
 137   if (fd != -1) {
 138     // We would like to ensure that the lock file is deleted when we are done
 139     // with it. The normal way to do that would be to call unlink on it right
 140     // now, but that would immediately delete the name from the file system, and
 141     // we need other instances to be able to open that name and get the same
 142     // inode, so we can't unlink the file before we're done with it. This means
 143     // we accept some unreliability in getting the file deleted, but it's a zero
 144     // byte file in the tmp directory, so having it stay around isn't the worst.
 145     struct flock l = {0};
 146     l.l_start = 0;
 147     l.l_len = 0;
 148     l.l_type = F_RDLCK;
 149     if (::fcntl(fd, F_SETLK, &l)) {
 150       ::close(fd);
 151       fd = -1;
 152     }
 153   }
 154   return fd;
 155
 156 #endif
 157 }
 158
 159 void ReleaseMultiInstanceLock(MultiInstLockHandle lock) {
 160   if (lock != MULTI_INSTANCE_LOCK_HANDLE_ERROR) {
 161 #ifdef XP_WIN
 162     OVERLAPPED o = {0};
 163     ::UnlockFileEx(lock, 0, 1, 0, &o);
 164     ::CloseHandle(lock);
 165
 166 #else
 167     // If we're the last instance, then unlink the lock file. There is a race
 168     // condition here that may cause an instance to fail to open the same inode
 169     // as another even though they use the same path, but there's no reasonable
 170     // way to avoid that without skipping deleting the file at all, so we accept
 171     // that risk.
 172     bool otherInstance = true;
 173     if (IsOtherInstanceRunning(lock, &otherInstance) && !otherInstance) {
 174       // Recover the file's path so we can unlink it.
 175       // There's no error checking in here because we're content to let the file
 176       // hang around if any of this fails (which can happen if for example we're
 177       // on a system where /proc/self/fd does not exist); this is a zero-byte
 178       // file in the tmp directory after all.
 179       UniquePtr<NS_tchar[]> linkPath = MakeUnique<NS_tchar[]>(MAXPATHLEN + 1);
 180       NS_tsnprintf(linkPath.get(), MAXPATHLEN + 1, "/proc/self/fd/%d", lock);
 181       UniquePtr<NS_tchar[]> lockFilePath =
 182           MakeUnique<NS_tchar[]>(MAXPATHLEN + 1);
 183       if (::readlink(linkPath.get(), lockFilePath.get(), MAXPATHLEN + 1) !=
 184           -1) {
 185         ::unlink(lockFilePath.get());
 186       }
 187     }
 188     // Now close the lock file, which will release the lock.
 189     ::close(lock);
 190 #endif
 191   }
 192 }
 193
 194 bool IsOtherInstanceRunning(MultiInstLockHandle lock, bool* aResult) {
 195   // Every running instance has opened a readonly lock, and read locks prevent
 196   // write locks from being opened, so to see if we are the only instance, we
 197   // attempt to take a write lock, and if it succeeds then that must mean there
 198   // are no other read locks open and therefore no other instances.
 199   if (lock == MULTI_INSTANCE_LOCK_HANDLE_ERROR) {
 200     return false;
 201   }
 202
 203 #ifdef XP_WIN
 204   // We need to release the lock we're holding before we would be allowed to
 205   // take an exclusive lock, and if that succeeds we need to release it too
 206   // in order to get our shared lock back. This procedure is not atomic, so we
 207   // accept the risk of the scheduler deciding to ruin our day between these
 208   // operations; we'd get a false negative in a different instance's check.
 209   OVERLAPPED o = {0};
 210   // Release our current shared lock.
 211   if (!::UnlockFileEx(lock, 0, 1, 0, &o)) {
 212     return false;
 213   }
 214   // Attempt to take an exclusive lock.
 215   bool rv = false;
 216   if (::LockFileEx(lock, LOCKFILE_EXCLUSIVE_LOCK | LOCKFILE_FAIL_IMMEDIATELY, 0,
 217                    1, 0, &o)) {
 218     // We got the exclusive lock, so now release it.
 219     ::UnlockFileEx(lock, 0, 1, 0, &o);
 220     *aResult = false;
 221     rv = true;
 222   } else if (::GetLastError() == ERROR_LOCK_VIOLATION) {
 223     // We didn't get the exclusive lock because of outstanding shared locks.
 224     *aResult = true;
 225     rv = true;
 226   }
 227   // Attempt to reclaim the shared lock we released at the beginning.
 228   if (!::LockFileEx(lock, LOCKFILE_FAIL_IMMEDIATELY, 0, 1, 0, &o)) {
 229     rv = false;
 230   }
 231   return rv;
 232
 233 #else
 234   // See if we would be allowed to set a write lock (no need to actually do so).
 235   struct flock l = {0};
 236   l.l_start = 0;
 237   l.l_len = 0;
 238   l.l_type = F_WRLCK;
 239   if (::fcntl(lock, F_GETLK, &l)) {
 240     return false;
 241   }
 242   *aResult = l.l_type != F_UNLCK;
 243   return true;
 244
 245 #endif
 246 }
 247
 248 already_AddRefed<nsIFile> GetNormalizedAppFile(nsIFile* aAppFile) {
 249   // If we're given an app file, use it; otherwise, get it from the ambient
 250   // directory service.
 251   nsresult rv;
 252   nsCOMPtr<nsIFile> appFile;
 253   if (aAppFile) {
 254     rv = aAppFile->Clone(getter_AddRefs(appFile));
 255     NS_ENSURE_SUCCESS(rv, nullptr);
 256   } else {
 257     nsCOMPtr<nsIProperties> dirSvc =
 258         do_GetService(NS_DIRECTORY_SERVICE_CONTRACTID);
 259     NS_ENSURE_TRUE(dirSvc, nullptr);
 260
 261     rv = dirSvc->Get(XRE_EXECUTABLE_FILE, NS_GET_IID(nsIFile),
 262                      getter_AddRefs(appFile));
 263     NS_ENSURE_SUCCESS(rv, nullptr);
 264   }
 265
 266   // It is possible that the path we have is on a case insensitive
 267   // filesystem in which case the path may vary depending on how the
 268   // application is called. We want to normalize the case somehow.
 269   // On Linux XRE_EXECUTABLE_FILE already seems to be set to the correct path.
 270   //
 271   // See similar nsXREDirProvider::GetInstallHash. The main difference here is
 272   // to allow lookup to fail on OSX, because some tests use a nonexistent
 273   // appFile.
 274 #ifdef XP_WIN
 275   // Windows provides a way to get the correct case.
 276   if (!mozilla::widget::WinUtils::ResolveJunctionPointsAndSymLinks(appFile)) {
 277     NS_WARNING("Failed to resolve install directory.");
 278   }
 279 #elif defined(MOZ_WIDGET_COCOA)
 280   // On OSX roundtripping through an FSRef fixes the case.
 281   FSRef ref;
 282   nsCOMPtr<nsILocalFileMac> macFile = do_QueryInterface(appFile);
 283   if (macFile && NS_SUCCEEDED(macFile->GetFSRef(&ref)) &&
 284       NS_SUCCEEDED(
 285           NS_NewLocalFileWithFSRef(&ref, true, getter_AddRefs(macFile)))) {
 286     appFile = static_cast<nsIFile*>(macFile);
 287   } else {
 288     NS_WARNING("Failed to resolve install directory.");
 289   }
 290 #endif
 291
 292   return appFile.forget();
 293 }
 294
 295 };  // namespace mozilla