| /* |
| * 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/stat.h> |
| #include <sys/types.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 |
| // that will be recreated across forks. In addition to files here, |
| // all files ending with ".jar" under /system/framework" are |
| // whitelisted. See FileDescriptorInfo::IsWhitelisted for the |
| // canonical definition. |
| static const char* kPathWhitelist[] = { |
| "/dev/null", |
| "/dev/pmsg0", |
| "/system/etc/event-log-tags", |
| "/sys/kernel/debug/tracing/trace_marker", |
| "/system/framework/framework-res.apk", |
| "/dev/urandom", |
| "/dev/ion" |
| }; |
| |
| 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; |
| } |
| |
| // Ignore (don't reopen or fail on) socket fds for now. |
| if (S_ISSOCK(f_stat.st_mode)) { |
| ALOGW("Unsupported socket FD: %d, ignoring.", fd); |
| 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 Reopen() const { |
| // Always skip over socket FDs for now. |
| if (is_sock) { |
| return true; |
| } |
| |
| // 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; |
| } |
| |
| if (close(new_fd) == -1) { |
| ALOGW("Failed close(%d) : %s", new_fd, strerror(errno)); |
| } |
| |
| 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; |
| } |
| |
| DISALLOW_COPY_AND_ASSIGN(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 re-opened, and false if an error occurred. |
| bool Reopen() { |
| 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->Reopen()) { |
| 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; |
| for (it = open_fd_map_.begin(); it != open_fd_map_.end(); ++it) { |
| 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. |
| open_fds.erase(element); |
| 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 { |
| // It's the same file. Nothing to do here. |
| } |
| } |
| } |
| |
| 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); |
| }; |