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Backport changes to whitelist sockets opened by the zygote.

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am: 7ec85f9d54

Change-Id: I6db56b5b06636201382f6d908297644183253c0b
This commit is contained in:
Narayan Kamath
2016-09-07 18:53:40 +00:00
committed by android-build-merger
parent 52d0f48f80 7ec85f9d54
commit f7b9f84f87
2 changed files with 588 additions and 0 deletions
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34
core/jni/com_android_internal_os_Zygote.cpp
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@ -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>
@ -50,6 +52,7 @@
#include "ScopedLocalRef.h"
#include "ScopedPrimitiveArray.h"
#include "ScopedUtfChars.h"
#include "fd_utils-inl.h"
#include "nativebridge/native_bridge.h"
@ -75,6 +78,12 @@ static void RuntimeAbort(JNIEnv* env) {
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;
@ -421,6 +430,9 @@ void ckTime(uint64_t start, const char* where) {
}
}
// 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,
@ -433,6 +445,23 @@ static pid_t ForkAndSpecializeCommon(JNIEnv* env, uid_t uid, gid_t gid, jintArra
SetSigChldHandler();
ckTime(start, "ForkAndSpecializeCommon:SetSigChldHandler");
// 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) {
@ -444,6 +473,11 @@ static pid_t ForkAndSpecializeCommon(JNIEnv* env, uid_t uid, gid_t gid, jintArra
DetachDescriptors(env, fdsToClose);
ckTime(start, "ForkAndSpecializeCommon:Fork and detach");
// 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) {

554
core/jni/fd_utils-inl.h Normal file
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@ -0,0 +1,554 @@
/*
* 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/alarm", /* Only on Android Lollipop and below. */
"/dev/null",
"/dev/pmsg0",
"/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::tr1::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::tr1::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::tr1::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::tr1::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);
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;
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::tr1::unordered_map<int, FileDescriptorInfo*> open_fd_map_;
// DISALLOW_COPY_AND_ASSIGN(FileDescriptorTable);
FileDescriptorTable(const FileDescriptorTable&);
void operator=(const FileDescriptorTable&);
};