base/memory/shared_memory_posix.cc

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "base/memory/shared_memory.h"
   6
   7 #include <errno.h>
   8 #include <fcntl.h>
   9 #include <sys/mman.h>
  10 #include <sys/stat.h>
  11 #include <sys/types.h>
  12 #include <unistd.h>
  13
  14 #include "base/file_util.h"
  15 #include "base/files/scoped_file.h"
  16 #include "base/lazy_instance.h"
  17 #include "base/logging.h"
  18 #include "base/process/process_metrics.h"
  19 #include "base/safe_strerror_posix.h"
  20 #include "base/strings/utf_string_conversions.h"
  21 #include "base/synchronization/lock.h"
  22 #include "base/threading/platform_thread.h"
  23 #include "base/threading/thread_restrictions.h"
  24
  25 #if defined(OS_MACOSX)
  26 #include "base/mac/foundation_util.h"
  27 #endif  // OS_MACOSX
  28
  29 #if defined(OS_ANDROID)
  30 #include "base/os_compat_android.h"
  31 #include "third_party/ashmem/ashmem.h"
  32 #endif
  33
  34 namespace base {
  35
  36 namespace {
  37
  38 LazyInstance<Lock>::Leaky g_thread_lock_ = LAZY_INSTANCE_INITIALIZER;
  39
  40 }
  41
  42 SharedMemory::SharedMemory()
  43     : mapped_file_(-1),
  44       readonly_mapped_file_(-1),
  45       inode_(0),
  46       mapped_size_(0),
  47       memory_(NULL),
  48       read_only_(false),
  49       requested_size_(0) {
  50 }
  51
  52 SharedMemory::SharedMemory(SharedMemoryHandle handle, bool read_only)
  53     : mapped_file_(handle.fd),
  54       readonly_mapped_file_(-1),
  55       inode_(0),
  56       mapped_size_(0),
  57       memory_(NULL),
  58       read_only_(read_only),
  59       requested_size_(0) {
  60   struct stat st;
  61   if (fstat(handle.fd, &st) == 0) {
  62     // If fstat fails, then the file descriptor is invalid and we'll learn this
  63     // fact when Map() fails.
  64     inode_ = st.st_ino;
  65   }
  66 }
  67
  68 SharedMemory::SharedMemory(SharedMemoryHandle handle, bool read_only,
  69                            ProcessHandle process)
  70     : mapped_file_(handle.fd),
  71       readonly_mapped_file_(-1),
  72       inode_(0),
  73       mapped_size_(0),
  74       memory_(NULL),
  75       read_only_(read_only),
  76       requested_size_(0) {
  77   // We don't handle this case yet (note the ignored parameter); let's die if
  78   // someone comes calling.
  79   NOTREACHED();
  80 }
  81
  82 SharedMemory::~SharedMemory() {
  83   Close();
  84 }
  85
  86 // static
  87 bool SharedMemory::IsHandleValid(const SharedMemoryHandle& handle) {
  88   return handle.fd >= 0;
  89 }
  90
  91 // static
  92 SharedMemoryHandle SharedMemory::NULLHandle() {
  93   return SharedMemoryHandle();
  94 }
  95
  96 // static
  97 void SharedMemory::CloseHandle(const SharedMemoryHandle& handle) {
  98   DCHECK_GE(handle.fd, 0);
  99   if (close(handle.fd) < 0)
 100     DPLOG(ERROR) << "close";
 101 }
 102
 103 // static
 104 size_t SharedMemory::GetHandleLimit() {
 105   return base::GetMaxFds();
 106 }
 107
 108 bool SharedMemory::CreateAndMapAnonymous(size_t size) {
 109   return CreateAnonymous(size) && Map(size);
 110 }
 111
 112 #if !defined(OS_ANDROID)
 113 // Chromium mostly only uses the unique/private shmem as specified by
 114 // "name == L"". The exception is in the StatsTable.
 115 // TODO(jrg): there is no way to "clean up" all unused named shmem if
 116 // we restart from a crash.  (That isn't a new problem, but it is a problem.)
 117 // In case we want to delete it later, it may be useful to save the value
 118 // of mem_filename after FilePathForMemoryName().
 119 bool SharedMemory::Create(const SharedMemoryCreateOptions& options) {
 120   DCHECK_EQ(-1, mapped_file_);
 121   if (options.size == 0) return false;
 122
 123   if (options.size > static_cast<size_t>(std::numeric_limits<int>::max()))
 124     return false;
 125
 126   // This function theoretically can block on the disk, but realistically
 127   // the temporary files we create will just go into the buffer cache
 128   // and be deleted before they ever make it out to disk.
 129   base::ThreadRestrictions::ScopedAllowIO allow_io;
 130
 131   ScopedFILE fp;
 132   bool fix_size = true;
 133   ScopedFD readonly_fd;
 134
 135   FilePath path;
 136   if (options.name_deprecated == NULL || options.name_deprecated->empty()) {
 137     // It doesn't make sense to have a open-existing private piece of shmem
 138     DCHECK(!options.open_existing_deprecated);
 139     // Q: Why not use the shm_open() etc. APIs?
 140     // A: Because they're limited to 4mb on OS X.  FFFFFFFUUUUUUUUUUU
 141     FilePath directory;
 142     if (GetShmemTempDir(options.executable, &directory))
 143       fp.reset(CreateAndOpenTemporaryFileInDir(directory, &path));
 144
 145     if (fp) {
 146       // Also open as readonly so that we can ShareReadOnlyToProcess.
 147       readonly_fd.reset(HANDLE_EINTR(open(path.value().c_str(), O_RDONLY)));
 148       if (!readonly_fd.is_valid()) {
 149         DPLOG(ERROR) << "open(\"" << path.value() << "\", O_RDONLY) failed";
 150         fp.reset();
 151       }
 152       // Deleting the file prevents anyone else from mapping it in (making it
 153       // private), and prevents the need for cleanup (once the last fd is
 154       // closed, it is truly freed).
 155       if (unlink(path.value().c_str()))
 156         PLOG(WARNING) << "unlink";
 157     }
 158   } else {
 159     if (!FilePathForMemoryName(*options.name_deprecated, &path))
 160       return false;
 161
 162     // Make sure that the file is opened without any permission
 163     // to other users on the system.
 164     const mode_t kOwnerOnly = S_IRUSR | S_IWUSR;
 165
 166     // First, try to create the file.
 167     int fd = HANDLE_EINTR(
 168         open(path.value().c_str(), O_RDWR | O_CREAT | O_EXCL, kOwnerOnly));
 169     if (fd == -1 && options.open_existing_deprecated) {
 170       // If this doesn't work, try and open an existing file in append mode.
 171       // Opening an existing file in a world writable directory has two main
 172       // security implications:
 173       // - Attackers could plant a file under their control, so ownership of
 174       //   the file is checked below.
 175       // - Attackers could plant a symbolic link so that an unexpected file
 176       //   is opened, so O_NOFOLLOW is passed to open().
 177       fd = HANDLE_EINTR(
 178           open(path.value().c_str(), O_RDWR | O_APPEND | O_NOFOLLOW));
 179
 180       // Check that the current user owns the file.
 181       // If uid != euid, then a more complex permission model is used and this
 182       // API is not appropriate.
 183       const uid_t real_uid = getuid();
 184       const uid_t effective_uid = geteuid();
 185       struct stat sb;
 186       if (fd >= 0 &&
 187           (fstat(fd, &sb) != 0 || sb.st_uid != real_uid ||
 188            sb.st_uid != effective_uid)) {
 189         LOG(ERROR) <<
 190             "Invalid owner when opening existing shared memory file.";
 191         close(fd);
 192         return false;
 193       }
 194
 195       // An existing file was opened, so its size should not be fixed.
 196       fix_size = false;
 197     }
 198
 199     // Also open as readonly so that we can ShareReadOnlyToProcess.
 200     readonly_fd.reset(HANDLE_EINTR(open(path.value().c_str(), O_RDONLY)));
 201     if (!readonly_fd.is_valid()) {
 202       DPLOG(ERROR) << "open(\"" << path.value() << "\", O_RDONLY) failed";
 203       close(fd);
 204       fd = -1;
 205     }
 206     if (fd >= 0) {
 207       // "a+" is always appropriate: if it's a new file, a+ is similar to w+.
 208       fp.reset(fdopen(fd, "a+"));
 209     }
 210   }
 211   if (fp && fix_size) {
 212     // Get current size.
 213     struct stat stat;
 214     if (fstat(fileno(fp.get()), &stat) != 0)
 215       return false;
 216     const size_t current_size = stat.st_size;
 217     if (current_size != options.size) {
 218       if (HANDLE_EINTR(ftruncate(fileno(fp.get()), options.size)) != 0)
 219         return false;
 220     }
 221     requested_size_ = options.size;
 222   }
 223   if (fp == NULL) {
 224 #if !defined(OS_MACOSX)
 225     PLOG(ERROR) << "Creating shared memory in " << path.value() << " failed";
 226     FilePath dir = path.DirName();
 227     if (access(dir.value().c_str(), W_OK | X_OK) < 0) {
 228       PLOG(ERROR) << "Unable to access(W_OK|X_OK) " << dir.value();
 229       if (dir.value() == "/dev/shm") {
 230         LOG(FATAL) << "This is frequently caused by incorrect permissions on "
 231                    << "/dev/shm.  Try 'sudo chmod 1777 /dev/shm' to fix.";
 232       }
 233     }
 234 #else
 235     PLOG(ERROR) << "Creating shared memory in " << path.value() << " failed";
 236 #endif
 237     return false;
 238   }
 239
 240   return PrepareMapFile(fp.Pass(), readonly_fd.Pass());
 241 }
 242
 243 // Our current implementation of shmem is with mmap()ing of files.
 244 // These files need to be deleted explicitly.
 245 // In practice this call is only needed for unit tests.
 246 bool SharedMemory::Delete(const std::string& name) {
 247   FilePath path;
 248   if (!FilePathForMemoryName(name, &path))
 249     return false;
 250
 251   if (PathExists(path))
 252     return base::DeleteFile(path, false);
 253
 254   // Doesn't exist, so success.
 255   return true;
 256 }
 257
 258 bool SharedMemory::Open(const std::string& name, bool read_only) {
 259   FilePath path;
 260   if (!FilePathForMemoryName(name, &path))
 261     return false;
 262
 263   read_only_ = read_only;
 264
 265   const char *mode = read_only ? "r" : "r+";
 266   ScopedFILE fp(base::OpenFile(path, mode));
 267   ScopedFD readonly_fd(HANDLE_EINTR(open(path.value().c_str(), O_RDONLY)));
 268   if (!readonly_fd.is_valid()) {
 269     DPLOG(ERROR) << "open(\"" << path.value() << "\", O_RDONLY) failed";
 270   }
 271   return PrepareMapFile(fp.Pass(), readonly_fd.Pass());
 272 }
 273 #endif  // !defined(OS_ANDROID)
 274
 275 bool SharedMemory::MapAt(off_t offset, size_t bytes) {
 276   if (mapped_file_ == -1)
 277     return false;
 278
 279   if (bytes > static_cast<size_t>(std::numeric_limits<int>::max()))
 280     return false;
 281
 282   if (memory_)
 283     return false;
 284
 285 #if defined(OS_ANDROID)
 286   // On Android, Map can be called with a size and offset of zero to use the
 287   // ashmem-determined size.
 288   if (bytes == 0) {
 289     DCHECK_EQ(0, offset);
 290     int ashmem_bytes = ashmem_get_size_region(mapped_file_);
 291     if (ashmem_bytes < 0)
 292       return false;
 293     bytes = ashmem_bytes;
 294   }
 295 #endif
 296
 297   memory_ = mmap(NULL, bytes, PROT_READ | (read_only_ ? 0 : PROT_WRITE),
 298                  MAP_SHARED, mapped_file_, offset);
 299
 300   bool mmap_succeeded = memory_ != (void*)-1 && memory_ != NULL;
 301   if (mmap_succeeded) {
 302     mapped_size_ = bytes;
 303     DCHECK_EQ(0U, reinterpret_cast<uintptr_t>(memory_) &
 304         (SharedMemory::MAP_MINIMUM_ALIGNMENT - 1));
 305   } else {
 306     memory_ = NULL;
 307   }
 308
 309   return mmap_succeeded;
 310 }
 311
 312 bool SharedMemory::Unmap() {
 313   if (memory_ == NULL)
 314     return false;
 315
 316   munmap(memory_, mapped_size_);
 317   memory_ = NULL;
 318   mapped_size_ = 0;
 319   return true;
 320 }
 321
 322 SharedMemoryHandle SharedMemory::handle() const {
 323   return FileDescriptor(mapped_file_, false);
 324 }
 325
 326 void SharedMemory::Close() {
 327   Unmap();
 328
 329   if (mapped_file_ > 0) {
 330     if (close(mapped_file_) < 0)
 331       PLOG(ERROR) << "close";
 332     mapped_file_ = -1;
 333   }
 334   if (readonly_mapped_file_ > 0) {
 335     if (close(readonly_mapped_file_) < 0)
 336       PLOG(ERROR) << "close";
 337     readonly_mapped_file_ = -1;
 338   }
 339 }
 340
 341 void SharedMemory::LockDeprecated() {
 342   g_thread_lock_.Get().Acquire();
 343   LockOrUnlockCommon(F_LOCK);
 344 }
 345
 346 void SharedMemory::UnlockDeprecated() {
 347   LockOrUnlockCommon(F_ULOCK);
 348   g_thread_lock_.Get().Release();
 349 }
 350
 351 #if !defined(OS_ANDROID)
 352 bool SharedMemory::PrepareMapFile(ScopedFILE fp, ScopedFD readonly_fd) {
 353   DCHECK_EQ(-1, mapped_file_);
 354   DCHECK_EQ(-1, readonly_mapped_file_);
 355   if (fp == NULL || !readonly_fd.is_valid()) return false;
 356
 357   // This function theoretically can block on the disk, but realistically
 358   // the temporary files we create will just go into the buffer cache
 359   // and be deleted before they ever make it out to disk.
 360   base::ThreadRestrictions::ScopedAllowIO allow_io;
 361
 362   struct stat st = {};
 363   struct stat readonly_st = {};
 364   if (fstat(fileno(fp.get()), &st))
 365     NOTREACHED();
 366   if (fstat(readonly_fd.get(), &readonly_st))
 367     NOTREACHED();
 368   if (st.st_dev != readonly_st.st_dev || st.st_ino != readonly_st.st_ino) {
 369     LOG(ERROR) << "writable and read-only inodes don't match; bailing";
 370     return false;
 371   }
 372
 373   mapped_file_ = dup(fileno(fp.get()));
 374   if (mapped_file_ == -1) {
 375     if (errno == EMFILE) {
 376       LOG(WARNING) << "Shared memory creation failed; out of file descriptors";
 377       return false;
 378     } else {
 379       NOTREACHED() << "Call to dup failed, errno=" << errno;
 380     }
 381   }
 382   inode_ = st.st_ino;
 383   readonly_mapped_file_ = readonly_fd.release();
 384
 385   return true;
 386 }
 387
 388 // For the given shmem named |mem_name|, return a filename to mmap()
 389 // (and possibly create).  Modifies |filename|.  Return false on
 390 // error, or true of we are happy.
 391 bool SharedMemory::FilePathForMemoryName(const std::string& mem_name,
 392                                          FilePath* path) {
 393   // mem_name will be used for a filename; make sure it doesn't
 394   // contain anything which will confuse us.
 395   DCHECK_EQ(std::string::npos, mem_name.find('/'));
 396   DCHECK_EQ(std::string::npos, mem_name.find('\0'));
 397
 398   FilePath temp_dir;
 399   if (!GetShmemTempDir(false, &temp_dir))
 400     return false;
 401
 402 #if !defined(OS_MACOSX)
 403 #if defined(GOOGLE_CHROME_BUILD)
 404   std::string name_base = std::string("com.google.Chrome");
 405 #else
 406   std::string name_base = std::string("org.chromium.Chromium");
 407 #endif
 408 #else  // OS_MACOSX
 409   std::string name_base = std::string(base::mac::BaseBundleID());
 410 #endif  // OS_MACOSX
 411   *path = temp_dir.AppendASCII(name_base + ".shmem." + mem_name);
 412   return true;
 413 }
 414 #endif  // !defined(OS_ANDROID)
 415
 416 void SharedMemory::LockOrUnlockCommon(int function) {
 417   DCHECK_GE(mapped_file_, 0);
 418   while (lockf(mapped_file_, function, 0) < 0) {
 419     if (errno == EINTR) {
 420       continue;
 421     } else if (errno == ENOLCK) {
 422       // temporary kernel resource exaustion
 423       base::PlatformThread::Sleep(base::TimeDelta::FromMilliseconds(500));
 424       continue;
 425     } else {
 426       NOTREACHED() << "lockf() failed."
 427                    << " function:" << function
 428                    << " fd:" << mapped_file_
 429                    << " errno:" << errno
 430                    << " msg:" << safe_strerror(errno);
 431     }
 432   }
 433 }
 434
 435 bool SharedMemory::ShareToProcessCommon(ProcessHandle process,
 436                                         SharedMemoryHandle* new_handle,
 437                                         bool close_self,
 438                                         ShareMode share_mode) {
 439   int handle_to_dup = -1;
 440   switch(share_mode) {
 441     case SHARE_CURRENT_MODE:
 442       handle_to_dup = mapped_file_;
 443       break;
 444     case SHARE_READONLY:
 445       // We could imagine re-opening the file from /dev/fd, but that can't make
 446       // it readonly on Mac: https://codereview.chromium.org/27265002/#msg10
 447       CHECK(readonly_mapped_file_ >= 0);
 448       handle_to_dup = readonly_mapped_file_;
 449       break;
 450   }
 451
 452   const int new_fd = dup(handle_to_dup);
 453   if (new_fd < 0) {
 454     DPLOG(ERROR) << "dup() failed.";
 455     return false;
 456   }
 457
 458   new_handle->fd = new_fd;
 459   new_handle->auto_close = true;
 460
 461   if (close_self)
 462     Close();
 463
 464   return true;
 465 }
 466
 467 }  // namespace base