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Commit 183a5d3c authored by Andreas Gampe's avatar Andreas Gampe
Browse files

Frameworks: Refactor FileDescriptorTable errors 

Surface error messages to the caller.

Bug: 74531335
Test: m
Test: Device boots
Change-Id: I14df050feb7f5417bb08d190492c3050cdbb1c1d
parent bf94c2c1

core/jni/com_android_internal_os_Zygote.cpp

+6 −6
Original line number Diff line number Diff line
@@ -591,12 +591,12 @@ static pid_t ForkAndSpecializeCommon(JNIEnv* env, uid_t uid, gid_t gid, jintArra 
    fail_fn(error_msg);

  }

  if (gOpenFdTable == NULL) {

    gOpenFdTable = FileDescriptorTable::Create(fds_to_ignore);

    gOpenFdTable = FileDescriptorTable::Create(fds_to_ignore, &error_msg);

    if (gOpenFdTable == NULL) {

      fail_fn(CREATE_ERROR("Unable to construct file descriptor table."));

      fail_fn(error_msg);

    }

  } else if (!gOpenFdTable->Restat(fds_to_ignore)) {

    fail_fn(CREATE_ERROR("Unable to restat file descriptor table."));

  } else if (!gOpenFdTable->Restat(fds_to_ignore, &error_msg)) {

    fail_fn(error_msg);

  }



  pid_t pid = fork();
@@ -611,8 +611,8 @@ static pid_t ForkAndSpecializeCommon(JNIEnv* env, uid_t uid, gid_t gid, jintArra 


    // Re-open all remaining open file descriptors so that they aren't shared

    // with the zygote across a fork.

    if (!gOpenFdTable->ReopenOrDetach()) {

      fail_fn(CREATE_ERROR("Unable to reopen whitelisted descriptors."));

    if (!gOpenFdTable->ReopenOrDetach(&error_msg)) {

      fail_fn(error_msg);

    }



    if (sigprocmask(SIG_UNBLOCK, &sigchld, nullptr) == -1) {

core/jni/fd_utils.cpp

+122 −43
Original line number Diff line number Diff line
@@ -119,14 +119,57 @@ FileDescriptorWhitelist::FileDescriptorWhitelist() 


FileDescriptorWhitelist* FileDescriptorWhitelist::instance_ = nullptr;



// Keeps track of all relevant information (flags, offset etc.) of an

// open zygote file descriptor.

class FileDescriptorInfo {

 public:

  // Create a FileDescriptorInfo for a given file descriptor. Returns

  // |NULL| if an error occurred.

  static FileDescriptorInfo* CreateFromFd(int fd, std::string* error_msg);



  // Checks whether the file descriptor associated with this object

  // refers to the same description.

  bool Restat() const;



  bool ReopenOrDetach(std::string* error_msg) const;



  const int fd;

  const struct stat stat;

  const std::string file_path;

  const int open_flags;

  const int fd_flags;

  const int fs_flags;

  const off_t offset;

  const bool is_sock;



 private:

  FileDescriptorInfo(int fd);



  FileDescriptorInfo(struct stat stat, const std::string& file_path, int fd, int open_flags,

                     int fd_flags, int fs_flags, off_t offset);



  // Returns the locally-bound name of the socket |fd|. Returns true

  // iff. all of the following hold :

  //

  // - the socket's sa_family is AF_UNIX.

  // - the length of the path is greater than zero (i.e, not an unnamed socket).

  // - the first byte of the path isn't zero (i.e, not a socket with an abstract

  //   address).

  static bool GetSocketName(const int fd, std::string* result);



  bool DetachSocket(std::string* error_msg) const;



  DISALLOW_COPY_AND_ASSIGN(FileDescriptorInfo);

};



// static

FileDescriptorInfo* FileDescriptorInfo::CreateFromFd(int fd) {

FileDescriptorInfo* FileDescriptorInfo::CreateFromFd(int fd, std::string* error_msg) {

  struct stat f_stat;

  // This should never happen; the zygote should always have the right set

  // of permissions required to stat all its open files.

  if (TEMP_FAILURE_RETRY(fstat(fd, &f_stat)) == -1) {

    PLOG(ERROR) << "Unable to stat fd " << fd;

    return NULL;

    *error_msg = android::base::StringPrintf("Unable to stat %d", fd);

    return nullptr;

  }



  const FileDescriptorWhitelist* whitelist = FileDescriptorWhitelist::Get();
@@ -134,13 +177,15 @@ FileDescriptorInfo* FileDescriptorInfo::CreateFromFd(int fd) { 
  if (S_ISSOCK(f_stat.st_mode)) {

    std::string socket_name;

    if (!GetSocketName(fd, &socket_name)) {

      return NULL;

      *error_msg = "Unable to get socket name";

      return nullptr;

    }



    if (!whitelist->IsAllowed(socket_name)) {

      LOG(ERROR) << "Socket name not whitelisted : " << socket_name

                 << " (fd=" << fd << ")";

      return NULL;

      *error_msg = android::base::StringPrintf("Socket name not whitelisted : %s (fd=%d)",

                                               socket_name.c_str(),

                                               fd);

      return nullptr;

    }



    return new FileDescriptorInfo(fd);
@@ -157,19 +202,22 @@ FileDescriptorInfo* FileDescriptorInfo::CreateFromFd(int fd) { 
  // with the child process across forks but those should have been closed

  // before we got to this point.

  if (!S_ISCHR(f_stat.st_mode) && !S_ISREG(f_stat.st_mode)) {

    LOG(ERROR) << "Unsupported st_mode " << f_stat.st_mode;

    return NULL;

    *error_msg = android::base::StringPrintf("Unsupported st_mode %u", f_stat.st_mode);

    return nullptr;

  }



  std::string file_path;

  const std::string fd_path = android::base::StringPrintf("/proc/self/fd/%d", fd);

  if (!android::base::Readlink(fd_path, &file_path)) {

    return NULL;

    *error_msg = android::base::StringPrintf("Could not read fd link %s: %s",

                                             fd_path.c_str(),

                                             strerror(errno));

    return nullptr;

  }



  if (!whitelist->IsAllowed(file_path)) {

    LOG(ERROR) << "Not whitelisted : " << file_path;

    return NULL;

    *error_msg = std::string("Not whitelisted : ").append(file_path);

    return nullptr;

  }



  // File descriptor flags : currently on FD_CLOEXEC. We can set these
@@ -177,8 +225,11 @@ FileDescriptorInfo* FileDescriptorInfo::CreateFromFd(int fd) { 
  // there won't be any races.

  const int fd_flags = TEMP_FAILURE_RETRY(fcntl(fd, F_GETFD));

  if (fd_flags == -1) {

    PLOG(ERROR) << "Failed fcntl(" << fd << ", F_GETFD)";

    return NULL;

    *error_msg = android::base::StringPrintf("Failed fcntl(%d, F_GETFD) (%s): %s",

                                             fd,

                                             file_path.c_str(),

                                             strerror(errno));

    return nullptr;

  }



  // File status flags :
@@ -195,8 +246,11 @@ FileDescriptorInfo* FileDescriptorInfo::CreateFromFd(int fd) { 
  //   their presence and pass them in to open().

  int fs_flags = TEMP_FAILURE_RETRY(fcntl(fd, F_GETFL));

  if (fs_flags == -1) {

    PLOG(ERROR) << "Failed fcntl(" << fd << ", F_GETFL)";

    return NULL;

    *error_msg = android::base::StringPrintf("Failed fcntl(%d, F_GETFL) (%s): %s",

                                             fd,

                                             file_path.c_str(),

                                             strerror(errno));

    return nullptr;

  }



  // File offset : Ignore the offset for non seekable files.
@@ -221,9 +275,9 @@ bool FileDescriptorInfo::Restat() const { 
  return f_stat.st_ino == stat.st_ino && f_stat.st_dev == stat.st_dev;

}



bool FileDescriptorInfo::ReopenOrDetach() const {

bool FileDescriptorInfo::ReopenOrDetach(std::string* error_msg) const {

  if (is_sock) {

    return DetachSocket();

    return DetachSocket(error_msg);

  }



  // NOTE: This might happen if the file was unlinked after being opened.
@@ -232,31 +286,49 @@ bool FileDescriptorInfo::ReopenOrDetach() const { 
  const int new_fd = TEMP_FAILURE_RETRY(open(file_path.c_str(), open_flags));



  if (new_fd == -1) {

    PLOG(ERROR) << "Failed open(" << file_path << ", " << open_flags << ")";

    *error_msg = android::base::StringPrintf("Failed open(%s, %i): %s",

                                             file_path.c_str(),

                                             open_flags,

                                             strerror(errno));

    return false;

  }



  if (TEMP_FAILURE_RETRY(fcntl(new_fd, F_SETFD, fd_flags)) == -1) {

    close(new_fd);

    PLOG(ERROR) << "Failed fcntl(" << new_fd << ", F_SETFD, " << fd_flags << ")";

    *error_msg = android::base::StringPrintf("Failed fcntl(%d, F_SETFD, %d) (%s): %s",

                                             new_fd,

                                             fd_flags,

                                             file_path.c_str(),

                                             strerror(errno));

    return false;

  }



  if (TEMP_FAILURE_RETRY(fcntl(new_fd, F_SETFL, fs_flags)) == -1) {

    close(new_fd);

    PLOG(ERROR) << "Failed fcntl(" << new_fd << ", F_SETFL, " << fs_flags << ")";

    *error_msg = android::base::StringPrintf("Failed fcntl(%d, F_SETFL, %d) (%s): %s",

                                             new_fd,

                                             fs_flags,

                                             file_path.c_str(),

                                             strerror(errno));

    return false;

  }



  if (offset != -1 && TEMP_FAILURE_RETRY(lseek64(new_fd, offset, SEEK_SET)) == -1) {

    close(new_fd);

    PLOG(ERROR) << "Failed lseek64(" << new_fd << ", SEEK_SET)";

    *error_msg = android::base::StringPrintf("Failed lseek64(%d, SEEK_SET) (%s): %s",

                                             new_fd,

                                             file_path.c_str(),

                                             strerror(errno));

    return false;

  }



  if (TEMP_FAILURE_RETRY(dup2(new_fd, fd)) == -1) {

    close(new_fd);

    PLOG(ERROR) << "Failed dup2(" << fd << ", " << new_fd << ")";

    *error_msg = android::base::StringPrintf("Failed dup2(%d, %d) (%s): %s",

                                             fd,

                                             new_fd,

                                             file_path.c_str(),

                                             strerror(errno));

    return false;

  }
@@ -332,20 +404,22 @@ bool FileDescriptorInfo::GetSocketName(const int fd, std::string* result) { 
  return true;

}



bool FileDescriptorInfo::DetachSocket() const {

bool FileDescriptorInfo::DetachSocket(std::string* error_msg) const {

  const int dev_null_fd = open("/dev/null", O_RDWR);

  if (dev_null_fd < 0) {

    PLOG(ERROR) << "Failed to open /dev/null";

    *error_msg = std::string("Failed to open /dev/null: ").append(strerror(errno));

    return false;

  }



  if (dup2(dev_null_fd, fd) == -1) {

    PLOG(ERROR) << "Failed dup2 on socket descriptor " << fd;

    *error_msg = android::base::StringPrintf("Failed dup2 on socket descriptor %d: %s",

                                             fd,

                                             strerror(errno));

    return false;

  }



  if (close(dev_null_fd) == -1) {

    PLOG(ERROR) << "Failed close(" << dev_null_fd << ")";

    *error_msg = android::base::StringPrintf("Failed close(%d): %s", dev_null_fd, strerror(errno));

    return false;

  }
@@ -353,11 +427,12 @@ bool FileDescriptorInfo::DetachSocket() const { 
}



// static

FileDescriptorTable* FileDescriptorTable::Create(const std::vector<int>& fds_to_ignore) {

FileDescriptorTable* FileDescriptorTable::Create(const std::vector<int>& fds_to_ignore,

                                                 std::string* error_msg) {

  DIR* d = opendir(kFdPath);

  if (d == NULL) {

    PLOG(ERROR) << "Unable to open directory " << std::string(kFdPath);

    return NULL;

  if (d == nullptr) {

    *error_msg = std::string("Unable to open directory ").append(kFdPath);

    return nullptr;

  }

  int dir_fd = dirfd(d);

  dirent* e;
@@ -373,7 +448,7 @@ FileDescriptorTable* FileDescriptorTable::Create(const std::vector<int>& fds_to_ 
      continue;

    }



    FileDescriptorInfo* info = FileDescriptorInfo::CreateFromFd(fd);

    FileDescriptorInfo* info = FileDescriptorInfo::CreateFromFd(fd, error_msg);

    if (info == NULL) {

      if (closedir(d) == -1) {

        PLOG(ERROR) << "Unable to close directory";
@@ -384,19 +459,21 @@ FileDescriptorTable* FileDescriptorTable::Create(const std::vector<int>& fds_to_ 
  }



  if (closedir(d) == -1) {

    PLOG(ERROR) << "Unable to close directory";

    return NULL;

    *error_msg = "Unable to close directory";

    return nullptr;

  }

  return new FileDescriptorTable(open_fd_map);

}



bool FileDescriptorTable::Restat(const std::vector<int>& fds_to_ignore) {

bool FileDescriptorTable::Restat(const std::vector<int>& fds_to_ignore, std::string* error_msg) {

  std::set<int> open_fds;



  // First get the list of open descriptors.

  DIR* d = opendir(kFdPath);

  if (d == NULL) {

    PLOG(ERROR) << "Unable to open directory " << std::string(kFdPath);

    *error_msg = android::base::StringPrintf("Unable to open directory %s: %s",

                                             kFdPath,

                                             strerror(errno));

    return false;

  }
@@ -416,21 +493,21 @@ bool FileDescriptorTable::Restat(const std::vector<int>& fds_to_ignore) { 
  }



  if (closedir(d) == -1) {

    PLOG(ERROR) << "Unable to close directory";

    *error_msg = android::base::StringPrintf("Unable to close directory: %s", strerror(errno));

    return false;

  }



  return RestatInternal(open_fds);

  return RestatInternal(open_fds, error_msg);

}



// Reopens all file descriptors that are contained in the table. Returns true

// if all descriptors were successfully re-opened or detached, and false if an

// error occurred.

bool FileDescriptorTable::ReopenOrDetach() {

bool FileDescriptorTable::ReopenOrDetach(std::string* error_msg) {

  std::unordered_map<int, FileDescriptorInfo*>::const_iterator it;

  for (it = open_fd_map_.begin(); it != open_fd_map_.end(); ++it) {

    const FileDescriptorInfo* info = it->second;

    if (info == NULL || !info->ReopenOrDetach()) {

    if (info == NULL || !info->ReopenOrDetach(error_msg)) {

      return false;

    }

  }
@@ -443,7 +520,7 @@ FileDescriptorTable::FileDescriptorTable( 
    : open_fd_map_(map) {

}



bool FileDescriptorTable::RestatInternal(std::set<int>& open_fds) {

bool FileDescriptorTable::RestatInternal(std::set<int>& open_fds, std::string* error_msg) {

  bool error = false;



  // Iterate through the list of file descriptors we've already recorded
@@ -451,6 +528,8 @@ bool FileDescriptorTable::RestatInternal(std::set<int>& open_fds) { 
  //

  // (a) they continue to be open.

  // (b) they refer to the same file.

  //

  // We'll only store the last error message.

  std::unordered_map<int, FileDescriptorInfo*>::iterator it = open_fd_map_.begin();

  while (it != open_fd_map_.end()) {

    std::set<int>::const_iterator element = open_fds.find(it->first);
@@ -471,7 +550,7 @@ bool FileDescriptorTable::RestatInternal(std::set<int>& open_fds) { 
        // The file descriptor refers to a different description. We must

        // update our entry in the table.

        delete it->second;

        it->second = FileDescriptorInfo::CreateFromFd(*element);

        it->second = FileDescriptorInfo::CreateFromFd(*element, error_msg);

        if (it->second == NULL) {

          // The descriptor no longer no longer refers to a whitelisted file.

          // We flag an error and remove it from the list of files we're
@@ -506,7 +585,7 @@ bool FileDescriptorTable::RestatInternal(std::set<int>& open_fds) { 
    std::set<int>::const_iterator it;

    for (it = open_fds.begin(); it != open_fds.end(); ++it) {

      const int fd = (*it);

      FileDescriptorInfo* info = FileDescriptorInfo::CreateFromFd(fd);

      FileDescriptorInfo* info = FileDescriptorInfo::CreateFromFd(fd, error_msg);

      if (info == NULL) {

        // A newly opened file is not on the whitelist. Flag an error and

        // continue.

core/jni/fd_utils.h

+7 −47
Original line number Diff line number Diff line
@@ -28,6 +28,8 @@ 


#include <android-base/macros.h>



class FileDescriptorInfo;



// Whitelist of open paths that the zygote is allowed to keep open.

//

// In addition to the paths listed in kPathWhitelist in file_utils.cpp, and
@@ -66,49 +68,6 @@ class FileDescriptorWhitelist { 
  DISALLOW_COPY_AND_ASSIGN(FileDescriptorWhitelist);

};



// Keeps track of all relevant information (flags, offset etc.) of an

// open zygote file descriptor.

class FileDescriptorInfo {

 public:

  // Create a FileDescriptorInfo for a given file descriptor. Returns

  // |NULL| if an error occurred.

  static FileDescriptorInfo* CreateFromFd(int fd);



  // Checks whether the file descriptor associated with this object

  // refers to the same description.

  bool Restat() const;



  bool ReopenOrDetach() const;



  const int fd;

  const struct stat stat;

  const std::string file_path;

  const int open_flags;

  const int fd_flags;

  const int fs_flags;

  const off_t offset;

  const bool is_sock;



 private:

  FileDescriptorInfo(int fd);



  FileDescriptorInfo(struct stat stat, const std::string& file_path, int fd, int open_flags,

                     int fd_flags, int fs_flags, off_t offset);



  // Returns the locally-bound name of the socket |fd|. Returns true

  // iff. all of the following hold :

  //

  // - the socket's sa_family is AF_UNIX.

  // - the length of the path is greater than zero (i.e, not an unnamed socket).

  // - the first byte of the path isn't zero (i.e, not a socket with an abstract

  //   address).

  static bool GetSocketName(const int fd, std::string* result);



  bool DetachSocket() const;



  DISALLOW_COPY_AND_ASSIGN(FileDescriptorInfo);

};



// A FileDescriptorTable is a collection of FileDescriptorInfo objects

// keyed by their FDs.

class FileDescriptorTable {
@@ -116,19 +75,20 @@ class FileDescriptorTable { 
  // Creates a new FileDescriptorTable. This function scans

  // /proc/self/fd for the list of open file descriptors and collects

  // information about them. Returns NULL if an error occurs.

  static FileDescriptorTable* Create(const std::vector<int>& fds_to_ignore);

  static FileDescriptorTable* Create(const std::vector<int>& fds_to_ignore,

                                     std::string* error_msg);



  bool Restat(const std::vector<int>& fds_to_ignore);

  bool Restat(const std::vector<int>& fds_to_ignore, std::string* error_msg);



  // Reopens all file descriptors that are contained in the table. Returns true

  // if all descriptors were successfully re-opened or detached, and false if an

  // error occurred.

  bool ReopenOrDetach();

  bool ReopenOrDetach(std::string* error_msg);



 private:

  FileDescriptorTable(const std::unordered_map<int, FileDescriptorInfo*>& map);



  bool RestatInternal(std::set<int>& open_fds);

  bool RestatInternal(std::set<int>& open_fds, std::string* error_msg);



  static int ParseFd(dirent* e, int dir_fd);