Backport changes to whitelist sockets opened by the zygote.
This is the backport of the following commits :
Commit c5f27a7cb2ec816f483a65255034a1b57a8aa22:
-----------------------------------------------
Reopen whitelisted zygote file descriptors after a fork.
We don't want these descriptors to be shared post-fork, so we'll
have to close and reopen them when the zygote forks. The set of
open descriptors is checked against a whitelist and it is a fatal
error if a non whitelisted FD is opened. It is also a fatal error
if anything other than a regular file / character device or socket
is opened at the time of forking.
This work is done in two stages :
- An initial list of FDs is constructed and cached prior to the
first zygote fork.
- On each subsequent fork, we check whether the list of open FDs
has changed. We are currently tolerant of changes, but in the
longer term, it should be a fatal error if the set of open file
descriptors in the zygote changes.
- Post fork, we traverse the list of open descriptors and reopen
them if necessary.
bug: 30963384
Commit 3764a260f0c90dcb323caeda14baf903cc108759:
-----------------------------------------------
Add a whitelist of sockets on fork.
Maintain a whitelist of AF_UNIX sockets that are permitted
to exist at the time of forking. If an open socket does not belong
to the whitelist (or is not AF_UNIX), the process will abort. If an
open socket is whitelisted, it will be redirected to /dev/null after
a sucessful fork. This allows us to unify our handling of the special
zygote sockets (/dev/socket/zygote[_secondary]) with the existing
whitelist of non socket file descriptors.
This change also removes non-fatal ALOGW messages since they have the
side effect of reopening the logging socket.
bug: 30963384
Commit 0b76d6a28e6978151bf245a775329cdae5e574d5:
-----------------------------------------------
fd_utils: Fix broken usage of iterators.
There were two separate issues here :
- RestatInternal was using an iterator after a call to erase(). This
will not work because it will be invalidated.
- The "standard" for loop idiom for iterating over a map while making
structural changes to it is broken. Switch to a while loop and treat
cases where elements are erased differently from cases where they
aren't.
bug: 31092930
bug: 30963384
Plus additional changes:
-----------------------------------------------
- add /dev/__properties__ to the whitelist.
Change-Id: I709a7f4913e807a8fec8a58c81e98fe5b5222820
(cherry picked from commit 41ca1bce01af7e86aeff9009df54bbc81e3c77d0)
diff --git a/core/jni/com_android_internal_os_Zygote.cpp b/core/jni/com_android_internal_os_Zygote.cpp
index b431a3f..a1fef4a 100644
--- a/core/jni/com_android_internal_os_Zygote.cpp
+++ b/core/jni/com_android_internal_os_Zygote.cpp
@@ -16,6 +16,8 @@
#define LOG_TAG "Zygote"
+#include <sstream>
+
// sys/mount.h has to come before linux/fs.h due to redefinition of MS_RDONLY, MS_BIND, etc
#include <sys/mount.h>
#include <linux/fs.h>
@@ -53,6 +55,7 @@
#include "ScopedLocalRef.h"
#include "ScopedPrimitiveArray.h"
#include "ScopedUtfChars.h"
+#include "fd_utils-inl.h"
#include "nativebridge/native_bridge.h"
@@ -78,6 +81,12 @@
env->FatalError("RuntimeAbort");
}
+static void RuntimeAbort(JNIEnv* env, int line, const char* msg) {
+ std::ostringstream oss;
+ oss << __FILE__ << ":" << line << ": " << msg;
+ env->FatalError(oss.str().c_str());
+}
+
// This signal handler is for zygote mode, since the zygote must reap its children
static void SigChldHandler(int /*signal_number*/) {
pid_t pid;
@@ -439,6 +448,9 @@
}
#endif
+// The list of open zygote file descriptors.
+static FileDescriptorTable* gOpenFdTable = NULL;
+
// Utility routine to fork zygote and specialize the child process.
static pid_t ForkAndSpecializeCommon(JNIEnv* env, uid_t uid, gid_t gid, jintArray javaGids,
jint debug_flags, jobjectArray javaRlimits,
@@ -453,6 +465,22 @@
SetForkLoad(true);
#endif
+ // Close any logging related FDs before we start evaluating the list of
+ // file descriptors.
+ __android_log_close();
+
+ // If this is the first fork for this zygote, create the open FD table.
+ // If it isn't, we just need to check whether the list of open files has
+ // changed (and it shouldn't in the normal case).
+ if (gOpenFdTable == NULL) {
+ gOpenFdTable = FileDescriptorTable::Create();
+ if (gOpenFdTable == NULL) {
+ RuntimeAbort(env, __LINE__, "Unable to construct file descriptor table.");
+ }
+ } else if (!gOpenFdTable->Restat()) {
+ RuntimeAbort(env, __LINE__, "Unable to restat file descriptor table.");
+ }
+
pid_t pid = fork();
if (pid == 0) {
@@ -462,6 +490,12 @@
// Clean up any descriptors which must be closed immediately
DetachDescriptors(env, fdsToClose);
+ // Re-open all remaining open file descriptors so that they aren't shared
+ // with the zygote across a fork.
+ if (!gOpenFdTable->ReopenOrDetach()) {
+ RuntimeAbort(env, __LINE__, "Unable to reopen whitelisted descriptors.");
+ }
+
// Keep capabilities across UID change, unless we're staying root.
if (uid != 0) {
EnableKeepCapabilities(env);
diff --git a/core/jni/fd_utils-inl.h b/core/jni/fd_utils-inl.h
new file mode 100644
index 0000000..a348745
--- /dev/null
+++ b/core/jni/fd_utils-inl.h
@@ -0,0 +1,552 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <string>
+#include <unordered_map>
+#include <set>
+#include <vector>
+#include <algorithm>
+
+#include <dirent.h>
+#include <fcntl.h>
+#include <grp.h>
+#include <inttypes.h>
+#include <stdlib.h>
+#include <sys/socket.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/un.h>
+#include <unistd.h>
+
+#include <cutils/log.h>
+#include "JNIHelp.h"
+#include "ScopedPrimitiveArray.h"
+
+// Whitelist of open paths that the zygote is allowed to keep open.
+//
+// In addition to the paths listed here, all files ending with
+// ".jar" under /system/framework" are whitelisted. See
+// FileDescriptorInfo::IsWhitelisted for the canonical definition.
+//
+// If the whitelisted path is associated with a regular file or a
+// character device, the file is reopened after a fork with the same
+// offset and mode. If the whilelisted path is associated with a
+// AF_UNIX socket, the socket will refer to /dev/null after each
+// fork, and all operations on it will fail.
+static const char* kPathWhitelist[] = {
+ "/dev/__properties__", /* Only on Android Lollipop and below. */
+ "/dev/null",
+ "/dev/socket/zygote",
+ "/dev/socket/zygote_secondary",
+ "/system/etc/event-log-tags",
+ "/sys/kernel/debug/tracing/trace_marker",
+ "/system/framework/framework-res.apk",
+ "/dev/urandom",
+ "/dev/ion",
+ "@netlink@"
+};
+
+static const char* kFdPath = "/proc/self/fd";
+
+// 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) {
+ 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) {
+ ALOGE("Unable to stat fd %d : %s", fd, strerror(errno));
+ return NULL;
+ }
+
+ if (S_ISSOCK(f_stat.st_mode)) {
+ std::string socket_name;
+ if (!GetSocketName(fd, &socket_name)) {
+ return NULL;
+ }
+
+ if (!IsWhitelisted(socket_name)) {
+ ALOGE("Socket name not whitelisted : %s (fd=%d)", socket_name.c_str(), fd);
+ return NULL;
+ }
+
+ return new FileDescriptorInfo(fd);
+ }
+
+ // We only handle whitelisted regular files and character devices. Whitelisted
+ // character devices must provide a guarantee of sensible behaviour when
+ // reopened.
+ //
+ // S_ISDIR : Not supported. (We could if we wanted to, but it's unused).
+ // S_ISLINK : Not supported.
+ // S_ISBLK : Not supported.
+ // S_ISFIFO : Not supported. Note that the zygote uses pipes to communicate
+ // 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)) {
+ ALOGE("Unsupported st_mode %d", f_stat.st_mode);
+ return NULL;
+ }
+
+ std::string file_path;
+ if (!Readlink(fd, &file_path)) {
+ return NULL;
+ }
+
+ if (!IsWhitelisted(file_path)) {
+ ALOGE("Not whitelisted : %s", file_path.c_str());
+ return NULL;
+ }
+
+ // File descriptor flags : currently on FD_CLOEXEC. We can set these
+ // using F_SETFD - we're single threaded at this point of execution so
+ // there won't be any races.
+ const int fd_flags = TEMP_FAILURE_RETRY(fcntl(fd, F_GETFD));
+ if (fd_flags == -1) {
+ ALOGE("Failed fcntl(%d, F_GETFD) : %s", fd, strerror(errno));
+ return NULL;
+ }
+
+ // File status flags :
+ // - File access mode : (O_RDONLY, O_WRONLY...) we'll pass these through
+ // to the open() call.
+ //
+ // - File creation flags : (O_CREAT, O_EXCL...) - there's not much we can
+ // do about these, since the file has already been created. We shall ignore
+ // them here.
+ //
+ // - Other flags : We'll have to set these via F_SETFL. On linux, F_SETFL
+ // can only set O_APPEND, O_ASYNC, O_DIRECT, O_NOATIME, and O_NONBLOCK.
+ // In particular, it can't set O_SYNC and O_DSYNC. We'll have to test for
+ // their presence and pass them in to open().
+ int fs_flags = TEMP_FAILURE_RETRY(fcntl(fd, F_GETFL));
+ if (fs_flags == -1) {
+ ALOGE("Failed fcntl(%d, F_GETFL) : %s", fd, strerror(errno));
+ return NULL;
+ }
+
+ // File offset : Ignore the offset for non seekable files.
+ const off_t offset = TEMP_FAILURE_RETRY(lseek64(fd, 0, SEEK_CUR));
+
+ // We pass the flags that open accepts to open, and use F_SETFL for
+ // the rest of them.
+ static const int kOpenFlags = (O_RDONLY | O_WRONLY | O_RDWR | O_DSYNC | O_SYNC);
+ int open_flags = fs_flags & (kOpenFlags);
+ fs_flags = fs_flags & (~(kOpenFlags));
+
+ return new FileDescriptorInfo(f_stat, file_path, fd, open_flags, fd_flags, fs_flags, offset);
+ }
+
+ // Checks whether the file descriptor associated with this object
+ // refers to the same description.
+ bool Restat() const {
+ struct stat f_stat;
+ if (TEMP_FAILURE_RETRY(fstat(fd, &f_stat)) == -1) {
+ return false;
+ }
+
+ return f_stat.st_ino == stat.st_ino && f_stat.st_dev == stat.st_dev;
+ }
+
+ bool ReopenOrDetach() const {
+ if (is_sock) {
+ return DetachSocket();
+ }
+
+ // NOTE: This might happen if the file was unlinked after being opened.
+ // It's a common pattern in the case of temporary files and the like but
+ // we should not allow such usage from the zygote.
+ const int new_fd = TEMP_FAILURE_RETRY(open(file_path.c_str(), open_flags));
+
+ if (new_fd == -1) {
+ ALOGE("Failed open(%s, %d) : %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);
+ ALOGE("Failed fcntl(%d, F_SETFD, %x) : %s", new_fd, fd_flags, strerror(errno));
+ return false;
+ }
+
+ if (TEMP_FAILURE_RETRY(fcntl(new_fd, F_SETFL, fs_flags)) == -1) {
+ close(new_fd);
+ ALOGE("Failed fcntl(%d, F_SETFL, %x) : %s", new_fd, fs_flags, strerror(errno));
+ return false;
+ }
+
+ if (offset != -1 && TEMP_FAILURE_RETRY(lseek64(new_fd, offset, SEEK_SET)) == -1) {
+ close(new_fd);
+ ALOGE("Failed lseek64(%d, SEEK_SET) : %s", new_fd, strerror(errno));
+ return false;
+ }
+
+ if (TEMP_FAILURE_RETRY(dup2(new_fd, fd)) == -1) {
+ close(new_fd);
+ ALOGE("Failed dup2(%d, %d) : %s", fd, new_fd, strerror(errno));
+ return false;
+ }
+
+ close(new_fd);
+
+ return true;
+ }
+
+ 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) :
+ fd(fd),
+ stat(),
+ open_flags(0),
+ fd_flags(0),
+ fs_flags(0),
+ offset(0),
+ is_sock(true) {
+ }
+
+ FileDescriptorInfo(struct stat stat, const std::string& file_path, int fd, int open_flags,
+ int fd_flags, int fs_flags, off_t offset) :
+ fd(fd),
+ stat(stat),
+ file_path(file_path),
+ open_flags(open_flags),
+ fd_flags(fd_flags),
+ fs_flags(fs_flags),
+ offset(offset),
+ is_sock(false) {
+ }
+
+ // Returns true iff. a given path is whitelisted. A path is whitelisted
+ // if it belongs to the whitelist (see kPathWhitelist) or if it's a path
+ // under /system/framework that ends with ".jar".
+ static bool IsWhitelisted(const std::string& path) {
+ for (size_t i = 0; i < (sizeof(kPathWhitelist) / sizeof(kPathWhitelist[0])); ++i) {
+ if (kPathWhitelist[i] == path) {
+ return true;
+ }
+ }
+
+ static const std::string kFrameworksPrefix = "/system/framework/";
+ static const std::string kJarSuffix = ".jar";
+ if (path.compare(0, kFrameworksPrefix.size(), kFrameworksPrefix) == 0 &&
+ path.compare(path.size() - kJarSuffix.size(), kJarSuffix.size(), kJarSuffix) == 0) {
+ return true;
+ }
+ return false;
+ }
+
+ // TODO: Call android::base::Readlink instead of copying the code here.
+ static bool Readlink(const int fd, std::string* result) {
+ char path[64];
+ snprintf(path, sizeof(path), "/proc/self/fd/%d", fd);
+
+ // Code copied from android::base::Readlink starts here :
+
+ // Annoyingly, the readlink system call returns EINVAL for a zero-sized buffer,
+ // and truncates to whatever size you do supply, so it can't be used to query.
+ // We could call lstat first, but that would introduce a race condition that
+ // we couldn't detect.
+ // ext2 and ext4 both have PAGE_SIZE limitations, so we assume that here.
+ char buf[4096];
+ ssize_t len = readlink(path, buf, sizeof(buf));
+ if (len == -1) return false;
+
+ result->assign(buf, len);
+ return true;
+ }
+
+ // 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) {
+ sockaddr_storage ss;
+ sockaddr* addr = reinterpret_cast<sockaddr*>(&ss);
+ socklen_t addr_len = sizeof(ss);
+
+ if (TEMP_FAILURE_RETRY(getsockname(fd, addr, &addr_len)) == -1) {
+ ALOGE("Failed getsockname(%d) : %s", fd, strerror(errno));
+ return false;
+ }
+
+
+ if (addr->sa_family == AF_NETLINK) {
+ (*result) = "@netlink@";
+ return true;
+ }
+
+ if (addr->sa_family != AF_UNIX) {
+ ALOGE("Unsupported socket (fd=%d) with family %d", fd, addr->sa_family);
+ return false;
+ }
+
+ const sockaddr_un* unix_addr = reinterpret_cast<const sockaddr_un*>(&ss);
+
+ size_t path_len = addr_len - offsetof(struct sockaddr_un, sun_path);
+ // This is an unnamed local socket, we do not accept it.
+ if (path_len == 0) {
+ ALOGE("Unsupported AF_UNIX socket (fd=%d) with empty path.", fd);
+ return false;
+ }
+
+ // This is a local socket with an abstract address, we do not accept it.
+ if (unix_addr->sun_path[0] == '\0') {
+ ALOGE("Unsupported AF_UNIX socket (fd=%d) with abstract address.", fd);
+ return false;
+ }
+
+ // If we're here, sun_path must refer to a null terminated filesystem
+ // pathname (man 7 unix). Remove the terminator before assigning it to an
+ // std::string.
+ if (unix_addr->sun_path[path_len - 1] == '\0') {
+ --path_len;
+ }
+
+ result->assign(unix_addr->sun_path, path_len);
+ return true;
+ }
+
+ bool DetachSocket() const {
+ const int dev_null_fd = open("/dev/null", O_RDWR);
+ if (dev_null_fd < 0) {
+ ALOGE("Failed to open /dev/null : %s", strerror(errno));
+ return false;
+ }
+
+ if (dup2(dev_null_fd, fd) == -1) {
+ ALOGE("Failed dup2 on socket descriptor %d : %s", fd, strerror(errno));
+ return false;
+ }
+
+ if (close(dev_null_fd) == -1) {
+ ALOGE("Failed close(%d) : %s", dev_null_fd, strerror(errno));
+ return false;
+ }
+
+ return true;
+ }
+
+
+ // DISALLOW_COPY_AND_ASSIGN(FileDescriptorInfo);
+ FileDescriptorInfo(const FileDescriptorInfo&);
+ void operator=(const FileDescriptorInfo&);
+};
+
+// A FileDescriptorTable is a collection of FileDescriptorInfo objects
+// keyed by their FDs.
+class FileDescriptorTable {
+ public:
+ // 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() {
+ DIR* d = opendir(kFdPath);
+ if (d == NULL) {
+ ALOGE("Unable to open directory %s: %s", kFdPath, strerror(errno));
+ return NULL;
+ }
+ int dir_fd = dirfd(d);
+ dirent* e;
+
+ std::unordered_map<int, FileDescriptorInfo*> open_fd_map;
+ while ((e = readdir(d)) != NULL) {
+ const int fd = ParseFd(e, dir_fd);
+ if (fd == -1) {
+ continue;
+ }
+
+ FileDescriptorInfo* info = FileDescriptorInfo::createFromFd(fd);
+ if (info == NULL) {
+ if (closedir(d) == -1) {
+ ALOGE("Unable to close directory : %s", strerror(errno));
+ }
+ return NULL;
+ }
+ open_fd_map[fd] = info;
+ }
+
+ if (closedir(d) == -1) {
+ ALOGE("Unable to close directory : %s", strerror(errno));
+ return NULL;
+ }
+ return new FileDescriptorTable(open_fd_map);
+ }
+
+ bool Restat() {
+ std::set<int> open_fds;
+
+ // First get the list of open descriptors.
+ DIR* d = opendir(kFdPath);
+ if (d == NULL) {
+ ALOGE("Unable to open directory %s: %s", kFdPath, strerror(errno));
+ return false;
+ }
+
+ int dir_fd = dirfd(d);
+ dirent* e;
+ while ((e = readdir(d)) != NULL) {
+ const int fd = ParseFd(e, dir_fd);
+ if (fd == -1) {
+ continue;
+ }
+
+ open_fds.insert(fd);
+ }
+
+ if (closedir(d) == -1) {
+ ALOGE("Unable to close directory : %s", strerror(errno));
+ return false;
+ }
+
+ return RestatInternal(open_fds);
+ }
+
+ // 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() {
+ 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()) {
+ return false;
+ }
+ }
+
+ return true;
+ }
+
+ private:
+ FileDescriptorTable(const std::unordered_map<int, FileDescriptorInfo*>& map)
+ : open_fd_map_(map) {
+ }
+
+ bool RestatInternal(std::set<int>& open_fds) {
+ bool error = false;
+
+ // Iterate through the list of file descriptors we've already recorded
+ // and check whether :
+ //
+ // (a) they continue to be open.
+ // (b) they refer to the same file.
+ 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);
+ if (element == open_fds.end()) {
+ // The entry from the file descriptor table is no longer in the list
+ // of open files. We warn about this condition and remove it from
+ // the list of FDs under consideration.
+ //
+ // TODO(narayan): This will be an error in a future android release.
+ // error = true;
+ // ALOGW("Zygote closed file descriptor %d.", it->first);
+ it = open_fd_map_.erase(it);
+ } else {
+ // The entry from the file descriptor table is still open. Restat
+ // it and check whether it refers to the same file.
+ const bool same_file = it->second->Restat();
+ if (!same_file) {
+ // The file descriptor refers to a different description. We must
+ // update our entry in the table.
+ delete it->second;
+ it->second = FileDescriptorInfo::createFromFd(*element);
+ 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
+ // tracking.
+ error = true;
+ it = open_fd_map_.erase(it);
+ } else {
+ // Successfully restatted the file, move on to the next open FD.
+ ++it;
+ }
+ } else {
+ // It's the same file. Nothing to do here. Move on to the next open
+ // FD.
+ ++it;
+ }
+
+ // Finally, remove the FD from the set of open_fds. We do this last because
+ // |element| will not remain valid after a call to erase.
+ open_fds.erase(*element);
+ }
+ }
+
+ if (open_fds.size() > 0) {
+ // The zygote has opened new file descriptors since our last inspection.
+ // We warn about this condition and add them to our table.
+ //
+ // TODO(narayan): This will be an error in a future android release.
+ // error = true;
+ // ALOGW("Zygote opened %zd new file descriptor(s).", open_fds.size());
+
+ // TODO(narayan): This code will be removed in a future android release.
+ 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);
+ if (info == NULL) {
+ // A newly opened file is not on the whitelist. Flag an error and
+ // continue.
+ error = true;
+ } else {
+ // Track the newly opened file.
+ open_fd_map_[fd] = info;
+ }
+ }
+ }
+
+ return !error;
+ }
+
+ static int ParseFd(dirent* e, int dir_fd) {
+ char* end;
+ const int fd = strtol(e->d_name, &end, 10);
+ if ((*end) != '\0') {
+ return -1;
+ }
+
+ // Don't bother with the standard input/output/error, they're handled
+ // specially post-fork anyway.
+ if (fd <= STDERR_FILENO || fd == dir_fd) {
+ return -1;
+ }
+
+ return fd;
+ }
+
+ // Invariant: All values in this unordered_map are non-NULL.
+ std::unordered_map<int, FileDescriptorInfo*> open_fd_map_;
+
+ // DISALLOW_COPY_AND_ASSIGN(FileDescriptorTable);
+ FileDescriptorTable(const FileDescriptorTable&);
+ void operator=(const FileDescriptorTable&);
+};
