| /* |
| * 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 "fd_utils.h" |
| |
| #include <algorithm> |
| |
| #include <fcntl.h> |
| #include <grp.h> |
| #include <stdlib.h> |
| #include <sys/socket.h> |
| #include <sys/types.h> |
| #include <sys/un.h> |
| #include <unistd.h> |
| |
| #include <android-base/file.h> |
| #include <android-base/logging.h> |
| #include <android-base/stringprintf.h> |
| #include <android-base/strings.h> |
| |
| // Static whitelist of open paths that the zygote is allowed to keep open. |
| static const char* kPathWhitelist[] = { |
| "/dev/null", |
| "/dev/socket/zygote", |
| "/dev/socket/zygote_secondary", |
| "/dev/socket/webview_zygote", |
| "/dev/socket/heapprofd", |
| "/sys/kernel/debug/tracing/trace_marker", |
| "/system/framework/framework-res.apk", |
| "/dev/urandom", |
| "/dev/ion", |
| "/dev/dri/renderD129", // Fixes b/31172436 |
| }; |
| |
| static const char kFdPath[] = "/proc/self/fd"; |
| |
| // static |
| FileDescriptorWhitelist* FileDescriptorWhitelist::Get() { |
| if (instance_ == nullptr) { |
| instance_ = new FileDescriptorWhitelist(); |
| } |
| return instance_; |
| } |
| |
| bool FileDescriptorWhitelist::IsAllowed(const std::string& path) const { |
| // Check the static whitelist path. |
| for (const auto& whitelist_path : kPathWhitelist) { |
| if (path == whitelist_path) |
| return true; |
| } |
| |
| // Check any paths added to the dynamic whitelist. |
| for (const auto& whitelist_path : whitelist_) { |
| if (path == whitelist_path) |
| return true; |
| } |
| |
| static const char* kFrameworksPrefix = "/system/framework/"; |
| static const char* kJarSuffix = ".jar"; |
| if (android::base::StartsWith(path, kFrameworksPrefix) |
| && android::base::EndsWith(path, kJarSuffix)) { |
| return true; |
| } |
| |
| // Whitelist files needed for Runtime Resource Overlay, like these: |
| // /system/vendor/overlay/framework-res.apk |
| // /system/vendor/overlay-subdir/pg/framework-res.apk |
| // /vendor/overlay/framework-res.apk |
| // /vendor/overlay/PG/android-framework-runtime-resource-overlay.apk |
| // /data/resource-cache/system@vendor@overlay@framework-res.apk@idmap |
| // /data/resource-cache/system@vendor@overlay-subdir@pg@framework-res.apk@idmap |
| // See AssetManager.cpp for more details on overlay-subdir. |
| static const char* kOverlayDir = "/system/vendor/overlay/"; |
| static const char* kVendorOverlayDir = "/vendor/overlay"; |
| static const char* kOverlaySubdir = "/system/vendor/overlay-subdir/"; |
| static const char* kSystemProductOverlayDir = "/system/product/overlay/"; |
| static const char* kProductOverlayDir = "/product/overlay"; |
| static const char* kApkSuffix = ".apk"; |
| |
| if ((android::base::StartsWith(path, kOverlayDir) |
| || android::base::StartsWith(path, kOverlaySubdir) |
| || android::base::StartsWith(path, kVendorOverlayDir) |
| || android::base::StartsWith(path, kSystemProductOverlayDir) |
| || android::base::StartsWith(path, kProductOverlayDir)) |
| && android::base::EndsWith(path, kApkSuffix) |
| && path.find("/../") == std::string::npos) { |
| return true; |
| } |
| |
| static const char* kOverlayIdmapPrefix = "/data/resource-cache/"; |
| static const char* kOverlayIdmapSuffix = ".apk@idmap"; |
| if (android::base::StartsWith(path, kOverlayIdmapPrefix) |
| && android::base::EndsWith(path, kOverlayIdmapSuffix) |
| && path.find("/../") == std::string::npos) { |
| return true; |
| } |
| |
| // All regular files that are placed under this path are whitelisted automatically. |
| static const char* kZygoteWhitelistPath = "/vendor/zygote_whitelist/"; |
| if (android::base::StartsWith(path, kZygoteWhitelistPath) |
| && path.find("/../") == std::string::npos) { |
| return true; |
| } |
| |
| return false; |
| } |
| |
| FileDescriptorWhitelist::FileDescriptorWhitelist() |
| : whitelist_() { |
| } |
| |
| 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, 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) { |
| *error_msg = android::base::StringPrintf("Unable to stat %d", fd); |
| return nullptr; |
| } |
| |
| const FileDescriptorWhitelist* whitelist = FileDescriptorWhitelist::Get(); |
| |
| if (S_ISSOCK(f_stat.st_mode)) { |
| std::string socket_name; |
| if (!GetSocketName(fd, &socket_name)) { |
| *error_msg = "Unable to get socket name"; |
| return nullptr; |
| } |
| |
| if (!whitelist->IsAllowed(socket_name)) { |
| *error_msg = android::base::StringPrintf("Socket name not whitelisted : %s (fd=%d)", |
| socket_name.c_str(), |
| fd); |
| return nullptr; |
| } |
| |
| 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)) { |
| *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)) { |
| *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)) { |
| *error_msg = std::string("Not whitelisted : ").append(file_path); |
| return nullptr; |
| } |
| |
| // 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) { |
| *error_msg = android::base::StringPrintf("Failed fcntl(%d, F_GETFD) (%s): %s", |
| fd, |
| file_path.c_str(), |
| strerror(errno)); |
| return nullptr; |
| } |
| |
| // 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) { |
| *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. |
| 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); |
| } |
| |
| bool FileDescriptorInfo::Restat() const { |
| struct stat f_stat; |
| if (TEMP_FAILURE_RETRY(fstat(fd, &f_stat)) == -1) { |
| PLOG(ERROR) << "Unable to restat fd " << fd; |
| return false; |
| } |
| |
| return f_stat.st_ino == stat.st_ino && f_stat.st_dev == stat.st_dev; |
| } |
| |
| bool FileDescriptorInfo::ReopenOrDetach(std::string* error_msg) const { |
| if (is_sock) { |
| return DetachSocket(error_msg); |
| } |
| |
| // 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) { |
| *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); |
| *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); |
| *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); |
| *error_msg = android::base::StringPrintf("Failed lseek64(%d, SEEK_SET) (%s): %s", |
| new_fd, |
| file_path.c_str(), |
| strerror(errno)); |
| return false; |
| } |
| |
| int dupFlags = (fd_flags & FD_CLOEXEC) ? O_CLOEXEC : 0; |
| if (TEMP_FAILURE_RETRY(dup3(new_fd, fd, dupFlags)) == -1) { |
| close(new_fd); |
| *error_msg = android::base::StringPrintf("Failed dup3(%d, %d, %d) (%s): %s", |
| fd, |
| new_fd, |
| dupFlags, |
| file_path.c_str(), |
| strerror(errno)); |
| return false; |
| } |
| |
| close(new_fd); |
| |
| return true; |
| } |
| |
| FileDescriptorInfo::FileDescriptorInfo(int fd) : |
| fd(fd), |
| stat(), |
| open_flags(0), |
| fd_flags(0), |
| fs_flags(0), |
| offset(0), |
| is_sock(true) { |
| } |
| |
| FileDescriptorInfo::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) { |
| } |
| |
| // static |
| bool FileDescriptorInfo::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) { |
| PLOG(ERROR) << "Failed getsockname(" << fd << ")"; |
| return false; |
| } |
| |
| if (addr->sa_family != AF_UNIX) { |
| LOG(ERROR) << "Unsupported socket (fd=" << fd << ") with family " << 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) { |
| LOG(ERROR) << "Unsupported AF_UNIX socket (fd=" << fd << ") with empty path."; |
| return false; |
| } |
| |
| // This is a local socket with an abstract address. Remove the leading NUL byte and |
| // add a human-readable "ABSTRACT/" prefix. |
| if (unix_addr->sun_path[0] == '\0') { |
| *result = "ABSTRACT/"; |
| result->append(&unix_addr->sun_path[1], path_len - 1); |
| return true; |
| } |
| |
| // 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 FileDescriptorInfo::DetachSocket(std::string* error_msg) const { |
| const int dev_null_fd = open("/dev/null", O_RDWR); |
| if (dev_null_fd < 0) { |
| *error_msg = std::string("Failed to open /dev/null: ").append(strerror(errno)); |
| return false; |
| } |
| |
| if (dup2(dev_null_fd, fd) == -1) { |
| *error_msg = android::base::StringPrintf("Failed dup2 on socket descriptor %d: %s", |
| fd, |
| strerror(errno)); |
| return false; |
| } |
| |
| if (close(dev_null_fd) == -1) { |
| *error_msg = android::base::StringPrintf("Failed close(%d): %s", dev_null_fd, strerror(errno)); |
| return false; |
| } |
| |
| return true; |
| } |
| |
| // static |
| FileDescriptorTable* FileDescriptorTable::Create(const std::vector<int>& fds_to_ignore, |
| std::string* error_msg) { |
| DIR* d = opendir(kFdPath); |
| if (d == nullptr) { |
| *error_msg = std::string("Unable to open directory ").append(kFdPath); |
| return nullptr; |
| } |
| 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; |
| } |
| if (std::find(fds_to_ignore.begin(), fds_to_ignore.end(), fd) != fds_to_ignore.end()) { |
| LOG(INFO) << "Ignoring open file descriptor " << fd; |
| continue; |
| } |
| |
| FileDescriptorInfo* info = FileDescriptorInfo::CreateFromFd(fd, error_msg); |
| if (info == NULL) { |
| if (closedir(d) == -1) { |
| PLOG(ERROR) << "Unable to close directory"; |
| } |
| return NULL; |
| } |
| open_fd_map[fd] = info; |
| } |
| |
| if (closedir(d) == -1) { |
| *error_msg = "Unable to close directory"; |
| return nullptr; |
| } |
| return new FileDescriptorTable(open_fd_map); |
| } |
| |
| 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) { |
| *error_msg = android::base::StringPrintf("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; |
| } |
| if (std::find(fds_to_ignore.begin(), fds_to_ignore.end(), fd) != fds_to_ignore.end()) { |
| LOG(INFO) << "Ignoring open file descriptor " << fd; |
| continue; |
| } |
| |
| open_fds.insert(fd); |
| } |
| |
| if (closedir(d) == -1) { |
| *error_msg = android::base::StringPrintf("Unable to close directory: %s", strerror(errno)); |
| return false; |
| } |
| |
| 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(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(error_msg)) { |
| return false; |
| } |
| } |
| |
| return true; |
| } |
| |
| FileDescriptorTable::FileDescriptorTable( |
| const std::unordered_map<int, FileDescriptorInfo*>& map) |
| : open_fd_map_(map) { |
| } |
| |
| 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 |
| // and check whether : |
| // |
| // (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); |
| 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, 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 |
| // 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, error_msg); |
| 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 FileDescriptorTable::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; |
| } |