text: // Copyright (c) 2012 The Chromium Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style license that can be
  // found in the LICENSE file.
  
  #include "base/memory/shared_memory.h"
  
  #include <errno.h>
  #include <fcntl.h>
  #include <sys/mman.h>
  #include <sys/stat.h>
  #include <sys/types.h>
  #include <unistd.h>
  
  #include "base/files/file_util.h"
  #include "base/files/scoped_file.h"
  #include "base/lazy_instance.h"
  #include "base/logging.h"
  #include "base/posix/eintr_wrapper.h"
  #include "base/process/process_metrics.h"
  #include "base/profiler/scoped_tracker.h"
  #include "base/safe_strerror_posix.h"
  #include "base/strings/utf_string_conversions.h"
  #include "base/synchronization/lock.h"
  #include "base/threading/platform_thread.h"
  #include "base/threading/thread_restrictions.h"
  
  #if defined(OS_MACOSX)
  #include "base/mac/foundation_util.h"
  #endif  // OS_MACOSX
  
  #if defined(OS_ANDROID)
  #include "base/os_compat_android.h"
  #include "third_party/ashmem/ashmem.h"
  #endif
  
  namespace base {
  
  namespace {
  
  LazyInstance<Lock>::Leaky g_thread_lock_ = LAZY_INSTANCE_INITIALIZER;
  
  }
  
  SharedMemory::SharedMemory()
      : mapped_file_(-1),
        readonly_mapped_file_(-1),
        inode_(0),
        mapped_size_(0),
        memory_(NULL),
        read_only_(false),
        requested_size_(0) {
  }
  
  SharedMemory::SharedMemory(SharedMemoryHandle handle, bool read_only)
      : mapped_file_(handle.fd),
        readonly_mapped_file_(-1),
        inode_(0),
        mapped_size_(0),
        memory_(NULL),
        read_only_(read_only),
        requested_size_(0) {
    struct stat st;
    if (fstat(handle.fd, &st) == 0) {
      // If fstat fails, then the file descriptor is invalid and we'll learn this
      // fact when Map() fails.
      inode_ = st.st_ino;
    }
  }
  
  SharedMemory::SharedMemory(SharedMemoryHandle handle, bool read_only,
                             ProcessHandle process)
      : mapped_file_(handle.fd),
        readonly_mapped_file_(-1),
        inode_(0),
        mapped_size_(0),
        memory_(NULL),
        read_only_(read_only),
        requested_size_(0) {
    // We don't handle this case yet (note the ignored parameter); let's die if
    // someone comes calling.
    NOTREACHED();
  }
  
  SharedMemory::~SharedMemory() {
    Unmap();
    Close();
  }
  
  // static
  bool SharedMemory::IsHandleValid(const SharedMemoryHandle& handle) {
    return handle.fd >= 0;
  }
  
  // static
  SharedMemoryHandle SharedMemory::NULLHandle() {
    return SharedMemoryHandle();
  }
  
  // static
  void SharedMemory::CloseHandle(const SharedMemoryHandle& handle) {
    DCHECK_GE(handle.fd, 0);
    if (close(handle.fd) < 0)
      DPLOG(ERROR) << "close";
  }
  
  // static
  size_t SharedMemory::GetHandleLimit() {
    return base::GetMaxFds();
  }
  
  bool SharedMemory::CreateAndMapAnonymous(size_t size) {
    return CreateAnonymous(size) && Map(size);
  }
  
  #if !defined(OS_ANDROID)
  // Chromium mostly only uses the unique/private shmem as specified by
  // "name == L"". The exception is in the StatsTable.
  // TODO(jrg): there is no way to "clean up" all unused named shmem if
  // we restart from a crash.  (That isn't a new problem, but it is a problem.)
  // In case we want to delete it later, it may be useful to save the value
  // of mem_filename after FilePathForMemoryName().
  bool SharedMemory::Create(const SharedMemoryCreateOptions& options) {
    // TODO(erikchen): Remove ScopedTracker below once http://crbug.com/466437
    // is fixed.
    tracked_objects::ScopedTracker tracking_profile1(
        FROM_HERE_WITH_EXPLICIT_FUNCTION(
            "466437 SharedMemory::Create::Start"));
    DCHECK_EQ(-1, mapped_file_);
    if (options.size == 0) return false;
  
    if (options.size > static_cast<size_t>(std::numeric_limits<int>::max()))
      return false;
  
    // This function theoretically can block on the disk, but realistically
    // the temporary files we create will just go into the buffer cache
    // and be deleted before they ever make it out to disk.
    base::ThreadRestrictions::ScopedAllowIO allow_io;
  
    ScopedFILE fp;
    bool fix_size = true;
    ScopedFD readonly_fd;
  
    FilePath path;
    if (options.name_deprecated == NULL || options.name_deprecated->empty()) {
      // It doesn't make sense to have a open-existing private piece of shmem
      DCHECK(!options.open_existing_deprecated);
      // Q: Why not use the shm_open() etc. APIs?
      // A: Because they're limited to 4mb on OS X.  FFFFFFFUUUUUUUUUUU
      FilePath directory;
      if (GetShmemTempDir(options.executable, &directory)) {
        // TODO(erikchen): Remove ScopedTracker below once http://crbug.com/466437
        // is fixed.
        tracked_objects::ScopedTracker tracking_profile2(
            FROM_HERE_WITH_EXPLICIT_FUNCTION(
                "466437 SharedMemory::Create::OpenTemporaryFile"));
        fp.reset(CreateAndOpenTemporaryFileInDir(directory, &path));
      }
  
      if (fp) {
        if (options.share_read_only) {
          // TODO(erikchen): Remove ScopedTracker below once
          // http://crbug.com/466437 is fixed.
          tracked_objects::ScopedTracker tracking_profile3(
              FROM_HERE_WITH_EXPLICIT_FUNCTION(
                  "466437 SharedMemory::Create::OpenReadonly"));
          // Also open as readonly so that we can ShareReadOnlyToProcess.
          readonly_fd.reset(HANDLE_EINTR(open(path.value().c_str(), O_RDONLY)));
          if (!readonly_fd.is_valid()) {
            DPLOG(ERROR) << "open(\"" << path.value() << "\", O_RDONLY) failed";
            fp.reset();
            return false;
          }
        }
  
        // TODO(erikchen): Remove ScopedTracker below once http://crbug.com/466437
        // is fixed.
        tracked_objects::ScopedTracker tracking_profile4(
            FROM_HERE_WITH_EXPLICIT_FUNCTION(
                "466437 SharedMemory::Create::Unlink"));
        // Deleting the file prevents anyone else from mapping it in (making it
        // private), and prevents the need for cleanup (once the last fd is
        // closed, it is truly freed).
        if (unlink(path.value().c_str()))
          PLOG(WARNING) << "unlink";
      }
    } else {
      if (!FilePathForMemoryName(*options.name_deprecated, &path))
        return false;
  
      // Make sure that the file is opened without any permission
      // to other users on the system.
      const mode_t kOwnerOnly = S_IRUSR | S_IWUSR;
  
      // First, try to create the file.
      int fd = HANDLE_EINTR(
          open(path.value().c_str(), O_RDWR | O_CREAT | O_EXCL, kOwnerOnly));
      if (fd == -1 && options.open_existing_deprecated) {
        // If this doesn't work, try and open an existing file in append mode.
        // Opening an existing file in a world writable directory has two main
        // security implications:
        // - Attackers could plant a file under their control, so ownership of
        //   the file is checked below.
        // - Attackers could plant a symbolic link so that an unexpected file
        //   is opened, so O_NOFOLLOW is passed to open().
        fd = HANDLE_EINTR(
            open(path.value().c_str(), O_RDWR | O_APPEND | O_NOFOLLOW));
  
        // Check that the current user owns the file.
        // If uid != euid, then a more complex permission model is used and this
        // API is not appropriate.
        const uid_t real_uid = getuid();
        const uid_t effective_uid = geteuid();
        struct stat sb;
        if (fd >= 0 &&
            (fstat(fd, &sb) != 0 || sb.st_uid != real_uid ||
             sb.st_uid != effective_uid)) {
          LOG(ERROR) <<
              "Invalid owner when opening existing shared memory file.";
          close(fd);
          return false;
        }
  
        // An existing file was opened, so its size should not be fixed.
        fix_size = false;
      }
  
      if (options.share_read_only) {
        // Also open as readonly so that we can ShareReadOnlyToProcess.
        readonly_fd.reset(HANDLE_EINTR(open(path.value().c_str(), O_RDONLY)));
        if (!readonly_fd.is_valid()) {
          DPLOG(ERROR) << "open(\"" << path.value() << "\", O_RDONLY) failed";
          close(fd);
          fd = -1;
          return false;
        }
      }
      if (fd >= 0) {
        // "a+" is always appropriate: if it's a new file, a+ is similar to w+.
        fp.reset(fdopen(fd, "a+"));
      }
    }
    if (fp && fix_size) {
      // Get current size.
      struct stat stat;
      if (fstat(fileno(fp.get()), &stat) != 0)
        return false;
      const size_t current_size = stat.st_size;
      if (current_size != options.size) {
        if (HANDLE_EINTR(ftruncate(fileno(fp.get()), options.size)) != 0)
          return false;
      }
      requested_size_ = options.size;
    }
    if (fp == NULL) {
  #if !defined(OS_MACOSX)
      PLOG(ERROR) << "Creating shared memory in " << path.value() << " failed";
      FilePath dir = path.DirName();
      if (access(dir.value().c_str(), W_OK | X_OK) < 0) {
        PLOG(ERROR) << "Unable to access(W_OK|X_OK) " << dir.value();
        if (dir.value() == "/dev/shm") {
          LOG(FATAL) << "This is frequently caused by incorrect permissions on "
                     << "/dev/shm.  Try 'sudo chmod 1777 /dev/shm' to fix.";
        }
      }
  #else
      PLOG(ERROR) << "Creating shared memory in " << path.value() << " failed";
  #endif
      return false;
    }
  
    return PrepareMapFile(fp.Pass(), readonly_fd.Pass());
  }
  
  // Our current implementation of shmem is with mmap()ing of files.
  // These files need to be deleted explicitly.
  // In practice this call is only needed for unit tests.
  bool SharedMemory::Delete(const std::string& name) {
    FilePath path;
    if (!FilePathForMemoryName(name, &path))
      return false;
  
    if (PathExists(path))
      return base::DeleteFile(path, false);
  
    // Doesn't exist, so success.
    return true;
  }
  
  bool SharedMemory::Open(const std::string& name, bool read_only) {
    FilePath path;
    if (!FilePathForMemoryName(name, &path))
      return false;
  
    read_only_ = read_only;
  
    const char *mode = read_only ? "r" : "r+";
    ScopedFILE fp(base::OpenFile(path, mode));
    ScopedFD readonly_fd(HANDLE_EINTR(open(path.value().c_str(), O_RDONLY)));
    if (!readonly_fd.is_valid()) {
      DPLOG(ERROR) << "open(\"" << path.value() << "\", O_RDONLY) failed";
      return false;
    }
    return PrepareMapFile(fp.Pass(), readonly_fd.Pass());
  }
  #endif  // !defined(OS_ANDROID)
  
  bool SharedMemory::MapAt(off_t offset, size_t bytes) {
    if (mapped_file_ == -1)
      return false;
  
    if (bytes > static_cast<size_t>(std::numeric_limits<int>::max()))
      return false;
  
    if (memory_)
      return false;
  
  #if defined(OS_ANDROID)
    // On Android, Map can be called with a size and offset of zero to use the
    // ashmem-determined size.
    if (bytes == 0) {
      DCHECK_EQ(0, offset);
      int ashmem_bytes = ashmem_get_size_region(mapped_file_);
      if (ashmem_bytes < 0)
        return false;
      bytes = ashmem_bytes;
    }
  #endif
  
    memory_ = mmap(NULL, bytes, PROT_READ | (read_only_ ? 0 : PROT_WRITE),
                   MAP_SHARED, mapped_file_, offset);
  
    bool mmap_succeeded = memory_ != (void*)-1 && memory_ != NULL;
    if (mmap_succeeded) {
      mapped_size_ = bytes;
      DCHECK_EQ(0U, reinterpret_cast<uintptr_t>(memory_) &
          (SharedMemory::MAP_MINIMUM_ALIGNMENT - 1));
    } else {
      memory_ = NULL;
    }
  
    return mmap_succeeded;
  }
  
  bool SharedMemory::Unmap() {
    if (memory_ == NULL)
      return false;
  
    munmap(memory_, mapped_size_);
    memory_ = NULL;
    mapped_size_ = 0;
    return true;
  }
  
  SharedMemoryHandle SharedMemory::handle() const {
    return FileDescriptor(mapped_file_, false);
  }
  
  void SharedMemory::Close() {
    if (mapped_file_ > 0) {
      if (close(mapped_file_) < 0)
        PLOG(ERROR) << "close";
      mapped_file_ = -1;
    }
    if (readonly_mapped_file_ > 0) {
      if (close(readonly_mapped_file_) < 0)
        PLOG(ERROR) << "close";
      readonly_mapped_file_ = -1;
    }
  }
  
  void SharedMemory::LockDeprecated() {
    g_thread_lock_.Get().Acquire();
    LockOrUnlockCommon(F_LOCK);
  }
  
  void SharedMemory::UnlockDeprecated() {
    LockOrUnlockCommon(F_ULOCK);
    g_thread_lock_.Get().Release();
  }
  
  #if !defined(OS_ANDROID)
  bool SharedMemory::PrepareMapFile(ScopedFILE fp, ScopedFD readonly_fd) {
    DCHECK_EQ(-1, mapped_file_);
    DCHECK_EQ(-1, readonly_mapped_file_);
    if (fp == NULL)
      return false;
  
    // This function theoretically can block on the disk, but realistically
    // the temporary files we create will just go into the buffer cache
    // and be deleted before they ever make it out to disk.
    base::ThreadRestrictions::ScopedAllowIO allow_io;
  
    struct stat st = {};
    if (fstat(fileno(fp.get()), &st))
      NOTREACHED();
    if (readonly_fd.is_valid()) {
      struct stat readonly_st = {};
      if (fstat(readonly_fd.get(), &readonly_st))
        NOTREACHED();
      if (st.st_dev != readonly_st.st_dev || st.st_ino != readonly_st.st_ino) {
        LOG(ERROR) << "writable and read-only inodes don't match; bailing";
        return false;
      }
    }
  
    mapped_file_ = HANDLE_EINTR(dup(fileno(fp.get())));
    if (mapped_file_ == -1) {
      if (errno == EMFILE) {
        LOG(WARNING) << "Shared memory creation failed; out of file descriptors";
        return false;
      } else {
        NOTREACHED() << "Call to dup failed, errno=" << errno;
      }
    }
    inode_ = st.st_ino;
    readonly_mapped_file_ = readonly_fd.release();
  
    return true;
  }
  
  // For the given shmem named |mem_name|, return a filename to mmap()
  // (and possibly create).  Modifies |filename|.  Return false on
  // error, or true of we are happy.
  bool SharedMemory::FilePathForMemoryName(const std::string& mem_name,
                                           FilePath* path) {
    // mem_name will be used for a filename; make sure it doesn't
    // contain anything which will confuse us.
    DCHECK_EQ(std::string::npos, mem_name.find('/'));
    DCHECK_EQ(std::string::npos, mem_name.find('\0'));
  
    FilePath temp_dir;
    if (!GetShmemTempDir(false, &temp_dir))
      return false;
  
  #if !defined(OS_MACOSX)
  #if defined(GOOGLE_CHROME_BUILD)
    std::string name_base = std::string("com.google.Chrome");
  #else
    std::string name_base = std::string("org.chromium.Chromium");
  #endif
  #else  // OS_MACOSX
    std::string name_base = std::string(base::mac::BaseBundleID());
  #endif  // OS_MACOSX
    *path = temp_dir.AppendASCII(name_base + ".shmem." + mem_name);
    return true;
  }
  #endif  // !defined(OS_ANDROID)
  
  void SharedMemory::LockOrUnlockCommon(int function) {
    DCHECK_GE(mapped_file_, 0);
    while (lockf(mapped_file_, function, 0) < 0) {
      if (errno == EINTR) {
        continue;
      } else if (errno == ENOLCK) {
        // temporary kernel resource exaustion
        base::PlatformThread::Sleep(base::TimeDelta::FromMilliseconds(500));
        continue;
      } else {
        NOTREACHED() << "lockf() failed."
                     << " function:" << function
                     << " fd:" << mapped_file_
                     << " errno:" << errno
                     << " msg:" << safe_strerror(errno);
      }
    }
  }
  
  bool SharedMemory::ShareToProcessCommon(ProcessHandle process,
                                          SharedMemoryHandle* new_handle,
                                          bool close_self,
                                          ShareMode share_mode) {
    int handle_to_dup = -1;
    switch(share_mode) {
      case SHARE_CURRENT_MODE:
        handle_to_dup = mapped_file_;
        break;
      case SHARE_READONLY:
        // We could imagine re-opening the file from /dev/fd, but that can't make
        // it readonly on Mac: https://codereview.chromium.org/27265002/#msg10
        CHECK_GE(readonly_mapped_file_, 0);
        handle_to_dup = readonly_mapped_file_;
        break;
    }
  
    const int new_fd = HANDLE_EINTR(dup(handle_to_dup));
    if (new_fd < 0) {
      DPLOG(ERROR) << "dup() failed.";
      return false;
    }
  
    new_handle->fd = new_fd;
    new_handle->auto_close = true;
  
    if (close_self) {
      Unmap();
      Close();
    }
  
    return true;
  }
  
  }  // namespace base
  