2143ee8d61
On a device where we can't BLKSECDISCARD sectors, we "overwrite" them with zeroes. This changes the FTL to remap those sectors to new locations. With this done, the old contents are accessible only given a compromise of flash firmware or a die level attack. Bug: 26021231 Change-Id: Ia065921389886fac1ba456c19c138187237c2561
232 lines
7.5 KiB
C++
232 lines
7.5 KiB
C++
/*
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* Copyright (C) 2015 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include <memory>
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#include <string>
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#include <vector>
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#include <stdio.h>
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#include <stdlib.h>
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#include <errno.h>
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <fcntl.h>
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#include <linux/fs.h>
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#include <linux/fiemap.h>
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#include <mntent.h>
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#include <android-base/logging.h>
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#include <AutoCloseFD.h>
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namespace {
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struct Options {
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std::vector<std::string> targets;
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bool unlink{true};
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};
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constexpr uint32_t max_extents = 32;
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bool read_command_line(int argc, const char * const argv[], Options &options);
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void usage(const char *progname);
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bool secdiscard_path(const std::string &path);
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std::unique_ptr<struct fiemap> path_fiemap(const std::string &path, uint32_t extent_count);
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bool check_fiemap(const struct fiemap &fiemap, const std::string &path);
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std::unique_ptr<struct fiemap> alloc_fiemap(uint32_t extent_count);
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std::string block_device_for_path(const std::string &path);
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bool overwrite_with_zeros(int fd, off64_t start, off64_t length);
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}
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int main(int argc, const char * const argv[]) {
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android::base::InitLogging(const_cast<char **>(argv));
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Options options;
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if (!read_command_line(argc, argv, options)) {
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usage(argv[0]);
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return -1;
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}
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for (auto const &target: options.targets) {
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LOG(DEBUG) << "Securely discarding '" << target << "' unlink=" << options.unlink;
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if (!secdiscard_path(target)) {
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LOG(ERROR) << "Secure discard failed for: " << target;
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}
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if (options.unlink) {
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if (unlink(target.c_str()) != 0 && errno != ENOENT) {
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PLOG(ERROR) << "Unable to unlink: " << target;
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}
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}
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LOG(DEBUG) << "Discarded: " << target;
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}
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return 0;
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}
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namespace {
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bool read_command_line(int argc, const char * const argv[], Options &options) {
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for (int i = 1; i < argc; i++) {
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if (!strcmp("--no-unlink", argv[i])) {
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options.unlink = false;
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} else if (!strcmp("--", argv[i])) {
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for (int j = i+1; j < argc; j++) {
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if (argv[j][0] != '/') return false; // Must be absolute path
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options.targets.emplace_back(argv[j]);
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}
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return options.targets.size() > 0;
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} else {
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return false; // Unknown option
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}
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}
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return false; // "--" not found
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}
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void usage(const char *progname) {
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fprintf(stderr, "Usage: %s [--no-unlink] -- <absolute path> ...\n", progname);
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}
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// BLKSECDISCARD all content in "path", if it's small enough.
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bool secdiscard_path(const std::string &path) {
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auto fiemap = path_fiemap(path, max_extents);
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if (!fiemap || !check_fiemap(*fiemap, path)) {
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return false;
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}
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auto block_device = block_device_for_path(path);
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if (block_device.empty()) {
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return false;
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}
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AutoCloseFD fs_fd(block_device, O_RDWR | O_LARGEFILE);
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if (!fs_fd) {
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PLOG(ERROR) << "Failed to open device " << block_device;
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return false;
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}
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for (uint32_t i = 0; i < fiemap->fm_mapped_extents; i++) {
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uint64_t range[2];
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range[0] = fiemap->fm_extents[i].fe_physical;
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range[1] = fiemap->fm_extents[i].fe_length;
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if (ioctl(fs_fd.get(), BLKSECDISCARD, range) == -1) {
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PLOG(ERROR) << "Unable to BLKSECDISCARD " << path;
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if (!overwrite_with_zeros(fs_fd.get(), range[0], range[1])) return false;
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LOG(DEBUG) << "Used zero overwrite";
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}
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}
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return true;
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}
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// Read the file's FIEMAP
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std::unique_ptr<struct fiemap> path_fiemap(const std::string &path, uint32_t extent_count)
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{
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AutoCloseFD fd(path);
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if (!fd) {
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if (errno == ENOENT) {
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PLOG(DEBUG) << "Unable to open " << path;
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} else {
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PLOG(ERROR) << "Unable to open " << path;
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}
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return nullptr;
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}
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auto fiemap = alloc_fiemap(extent_count);
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if (ioctl(fd.get(), FS_IOC_FIEMAP, fiemap.get()) != 0) {
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PLOG(ERROR) << "Unable to FIEMAP " << path;
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return nullptr;
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}
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auto mapped = fiemap->fm_mapped_extents;
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if (mapped < 1 || mapped > extent_count) {
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LOG(ERROR) << "Extent count not in bounds 1 <= " << mapped << " <= " << extent_count
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<< " in " << path;
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return nullptr;
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}
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return fiemap;
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}
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// Ensure that the FIEMAP covers the file and is OK to discard
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bool check_fiemap(const struct fiemap &fiemap, const std::string &path) {
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auto mapped = fiemap.fm_mapped_extents;
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if (!(fiemap.fm_extents[mapped - 1].fe_flags & FIEMAP_EXTENT_LAST)) {
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LOG(ERROR) << "Extent " << mapped -1 << " was not the last in " << path;
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return false;
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}
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for (uint32_t i = 0; i < mapped; i++) {
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auto flags = fiemap.fm_extents[i].fe_flags;
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if (flags & (FIEMAP_EXTENT_UNKNOWN | FIEMAP_EXTENT_DELALLOC | FIEMAP_EXTENT_NOT_ALIGNED)) {
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LOG(ERROR) << "Extent " << i << " has unexpected flags " << flags << ": " << path;
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return false;
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}
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}
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return true;
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}
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std::unique_ptr<struct fiemap> alloc_fiemap(uint32_t extent_count)
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{
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size_t allocsize = offsetof(struct fiemap, fm_extents[extent_count]);
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std::unique_ptr<struct fiemap> res(new (::operator new (allocsize)) struct fiemap);
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memset(res.get(), 0, allocsize);
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res->fm_start = 0;
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res->fm_length = UINT64_MAX;
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res->fm_flags = 0;
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res->fm_extent_count = extent_count;
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res->fm_mapped_extents = 0;
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return res;
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}
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// Given a file path, look for the corresponding block device in /proc/mount
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std::string block_device_for_path(const std::string &path)
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{
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std::unique_ptr<FILE, int(*)(FILE*)> mnts(setmntent("/proc/mounts", "re"), endmntent);
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if (!mnts) {
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PLOG(ERROR) << "Unable to open /proc/mounts";
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return "";
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}
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std::string result;
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size_t best_length = 0;
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struct mntent *mnt; // getmntent returns a thread local, so it's safe.
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while ((mnt = getmntent(mnts.get())) != nullptr) {
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auto l = strlen(mnt->mnt_dir);
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if (l > best_length &&
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path.size() > l &&
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path[l] == '/' &&
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path.compare(0, l, mnt->mnt_dir) == 0) {
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result = mnt->mnt_fsname;
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best_length = l;
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}
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}
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if (result.empty()) {
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LOG(ERROR) <<"Didn't find a mountpoint to match path " << path;
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return "";
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}
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LOG(DEBUG) << "For path " << path << " block device is " << result;
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return result;
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}
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bool overwrite_with_zeros(int fd, off64_t start, off64_t length) {
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if (lseek64(fd, start, SEEK_SET) != start) {
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PLOG(ERROR) << "Seek failed for zero overwrite";
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return false;
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}
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char buf[BUFSIZ];
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memset(buf, 0, sizeof(buf));
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while (length > 0) {
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size_t wlen = static_cast<size_t>(std::min(static_cast<off64_t>(sizeof(buf)), length));
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auto written = write(fd, buf, wlen);
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if (written < 1) {
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PLOG(ERROR) << "Write of zeroes failed";
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return false;
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}
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length -= written;
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}
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return true;
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}
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}
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