program to store unencrypted files in an encrypted filesystem

uncrypt can read a file on an encrypted filesystem and rewrite it to
the same blocks on the underlying (unencrypted) block device.  This
destroys the contents of the file as far as the encrypted filesystem
is concerned, but allows the data to be read without the encryption
key if you know which blocks of the raw device to access.  uncrypt
produces a "block map" file which lists the blocks that contain the file.

For unencrypted filesystem, uncrypt will produce the block map without
touching the data.

Bug: 12188746
Change-Id: Ib7259b9e14dac8af406796b429d58378a00c7c63

2 files changed, 405 insertions, 0 deletions

diff --git a/uncrypt/Android.mk b/uncrypt/Android.mk
new file mode 100644
index 0000000..756bc96
--- /dev/null
+++ b/uncrypt/Android.mk
@@ -0,0 +1,28 @@
+# Copyright (C) 2014 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.
+
+LOCAL_PATH := $(call my-dir)
+
+include $(CLEAR_VARS)
+
+LOCAL_SRC_FILES := uncrypt.c
+
+LOCAL_MODULE := uncrypt
+
+LOCAL_STATIC_LIBRARIES := \
+	libfs_mgr \
+	libcutils \
+	libc
+
+include $(BUILD_EXECUTABLE)
diff --git a/uncrypt/uncrypt.c b/uncrypt/uncrypt.c
new file mode 100644
index 0000000..1f0f59d
--- /dev/null
+++ b/uncrypt/uncrypt.c
@@ -0,0 +1,377 @@
+/*
+ * Copyright (C) 2014 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.
+ */
+
+// This program takes a file on an ext4 filesystem and produces a list
+// of the blocks that file occupies, which enables the file contents
+// to be read directly from the block device without mounting the
+// filesystem.
+//
+// If the filesystem is using an encrypted block device, it will also
+// read the file and rewrite it to the same blocks of the underlying
+// (unencrypted) block device, so the file contents can be read
+// without the need for the decryption key.
+//
+// The output of this program is a "block map" which looks like this:
+//
+//     /dev/block/platform/msm_sdcc.1/by-name/userdata     # block device
+//     49652 4096                        # file size in bytes, block size
+//     3                                 # count of block ranges
+//     1000 1008                         # block range 0
+//     2100 2102                         # ... block range 1
+//     30 33                             # ... block range 2
+//
+// Each block range represents a half-open interval; the line "30 33"
+// reprents the blocks [30, 31, 32].
+//
+// Recovery can take this block map file and retrieve the underlying
+// file data to use as an update package.
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdarg.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <linux/fs.h>
+#include <sys/mman.h>
+
+#include <cutils/properties.h>
+#include <fs_mgr.h>
+
+#define WINDOW_SIZE 5
+#define RECOVERY_COMMAND_FILE "/cache/recovery/command"
+#define RECOVERY_COMMAND_FILE_TMP "/cache/recovery/command.tmp"
+#define CACHE_BLOCK_MAP "/cache/recovery/block.map"
+
+static int write_at_offset(unsigned char* buffer, size_t size,
+                           int wfd, off64_t offset)
+{
+    lseek64(wfd, offset, SEEK_SET);
+    size_t written = 0;
+    while (written < size) {
+        ssize_t wrote = write(wfd, buffer + written, size - written);
+        if (wrote < 0) {
+            fprintf(stderr, "error writing offset %lld: %s\n", offset, strerror(errno));
+            return -1;
+        }
+        written += wrote;
+    }
+    return 0;
+}
+
+void add_block_to_ranges(int** ranges, int* range_alloc, int* range_used, int new_block)
+{
+    // If the current block start is < 0, set the start to the new
+    // block.  (This only happens for the very first block of the very
+    // first range.)
+    if ((*ranges)[*range_used*2-2] < 0) {
+        (*ranges)[*range_used*2-2] = new_block;
+        (*ranges)[*range_used*2-1] = new_block;
+    }
+
+    if (new_block == (*ranges)[*range_used*2-1]) {
+        // If the new block comes immediately after the current range,
+        // all we have to do is extend the current range.
+        ++(*ranges)[*range_used*2-1];
+    } else {
+        // We need to start a new range.
+
+        // If there isn't enough room in the array, we need to expand it.
+        if (*range_used >= *range_alloc) {
+            *range_alloc *= 2;
+            *ranges = realloc(*ranges, *range_alloc * 2 * sizeof(int));
+        }
+
+        ++*range_used;
+        (*ranges)[*range_used*2-2] = new_block;
+        (*ranges)[*range_used*2-1] = new_block+1;
+    }
+}
+
+const char* find_block_device(const char* path, int* encryptable, int* encrypted)
+{
+    // The fstab path is always "/fstab.${ro.hardware}".
+    char fstab_path[PATH_MAX+1] = "/fstab.";
+    if (!property_get("ro.hardware", fstab_path+strlen(fstab_path), "")) {
+        fprintf(stderr, "failed to get ro.hardware\n");
+        return NULL;
+    }
+
+    struct fstab* fstab = fs_mgr_read_fstab(fstab_path);
+    if (!fstab) {
+        fprintf(stderr, "failed to read %s\n", fstab_path);
+        return NULL;
+    }
+
+    // Look for a volume whose mount point is the prefix of path and
+    // return its block device.  Set encrypted if it's currently
+    // encrypted.
+    int i;
+    for (i = 0; i < fstab->num_entries; ++i) {
+        struct fstab_rec* v = &fstab->recs[i];
+        if (!v->mount_point) continue;
+        int len = strlen(v->mount_point);
+        if (strncmp(path, v->mount_point, len) == 0 &&
+            (path[len] == '/' || path[len] == 0)) {
+            *encrypted = 0;
+            *encryptable = 0;
+            if (fs_mgr_is_encryptable(v)) {
+                *encryptable = 1;
+                char buffer[PROPERTY_VALUE_MAX+1];
+                if (property_get("ro.crypto.state", buffer, "") &&
+                    strcmp(buffer, "encrypted") == 0) {
+                    *encrypted = 1;
+                }
+            }
+            return v->blk_device;
+        }
+    }
+
+    return NULL;
+}
+
+char* parse_recovery_command_file()
+{
+    char* fn = NULL;
+    int count = 0;
+    char temp[1024];
+
+    FILE* fo = fopen(RECOVERY_COMMAND_FILE_TMP, "w");
+
+    FILE* f = fopen(RECOVERY_COMMAND_FILE, "r");
+    while (fgets(temp, sizeof(temp), f)) {
+        printf("read: %s", temp);
+        if (strncmp(temp, "--update_package=", strlen("--update_package=")) == 0) {
+            fn = strdup(temp + strlen("--update_package="));
+            strcpy(temp, "--update_package=@" CACHE_BLOCK_MAP "\n");
+        }
+        fputs(temp, fo);
+    }
+    fclose(f);
+    fclose(fo);
+
+    if (fn) {
+        char* newline = strchr(fn, '\n');
+        if (newline) *newline = 0;
+    }
+    return fn;
+}
+
+int produce_block_map(const char* path, const char* map_file, const char* blk_dev,
+                      int encrypted)
+{
+    struct stat sb;
+    int ret;
+
+    FILE* mapf = fopen(map_file, "w");
+
+    ret = stat(path, &sb);
+    if (ret != 0) {
+        fprintf(stderr, "failed to stat %s\n", path);
+        return -1;
+    }
+
+    printf(" block size: %ld bytes\n", sb.st_blksize);
+
+    int blocks = ((sb.st_size-1) / sb.st_blksize) + 1;
+    printf("  file size: %lld bytes, %d blocks\n", sb.st_size, blocks);
+
+    int* ranges;
+    int range_alloc = 1;
+    int range_used = 1;
+    ranges = malloc(range_alloc * 2 * sizeof(int));
+    ranges[0] = -1;
+    ranges[1] = -1;
+
+    fprintf(mapf, "%s\n%lld %lu\n", blk_dev, sb.st_size, sb.st_blksize);
+
+    unsigned char* buffers[WINDOW_SIZE];
+    int i;
+    if (encrypted) {
+        for (i = 0; i < WINDOW_SIZE; ++i) {
+            buffers[i] = malloc(sb.st_blksize);
+        }
+    }
+    int head_block = 0;
+    int head = 0, tail = 0;
+    size_t pos = 0;
+
+    int fd = open(path, O_RDONLY);
+    if (fd < 0) {
+        fprintf(stderr, "failed to open fd for reading: %s\n", strerror(errno));
+        return -1;
+    }
+    fsync(fd);
+
+    int wfd = -1;
+    if (encrypted) {
+        wfd = open(blk_dev, O_WRONLY);
+        if (wfd < 0) {
+            fprintf(stderr, "failed to open fd for writing: %s\n", strerror(errno));
+            return -1;
+        }
+    }
+
+    while (pos < sb.st_size) {
+        if ((tail+1) % WINDOW_SIZE == head) {
+            // write out head buffer
+            int block = head_block;
+            ret = ioctl(fd, FIBMAP, &block);
+            if (ret != 0) {
+                fprintf(stderr, "failed to find block %d\n", head_block);
+                return -1;
+            }
+            add_block_to_ranges(&ranges, &range_alloc, &range_used, block);
+            if (encrypted) {
+                if (write_at_offset(buffers[head], sb.st_blksize, wfd, (off64_t)sb.st_blksize * block) != 0) {
+                    return -1;
+                }
+            }
+            head = (head + 1) % WINDOW_SIZE;
+            ++head_block;
+        }
+
+        // read next block to tail
+        if (encrypted) {
+            size_t so_far = 0;
+            while (so_far < sb.st_blksize && pos < sb.st_size) {
+                ssize_t this_read = read(fd, buffers[tail] + so_far, sb.st_blksize - so_far);
+                if (this_read < 0) {
+                    fprintf(stderr, "failed to read: %s\n", strerror(errno));
+                    return -1;
+                }
+                so_far += this_read;
+                pos += this_read;
+            }
+        } else {
+            // If we're not encrypting; we don't need to actually read
+            // anything, just skip pos forward as if we'd read a
+            // block.
+            pos += sb.st_blksize;
+        }
+        tail = (tail+1) % WINDOW_SIZE;
+    }
+
+    while (head != tail) {
+        // write out head buffer
+        int block = head_block;
+        ret = ioctl(fd, FIBMAP, &block);
+        if (ret != 0) {
+            fprintf(stderr, "failed to find block %d\n", head_block);
+            return -1;
+        }
+        add_block_to_ranges(&ranges, &range_alloc, &range_used, block);
+        if (encrypted) {
+            if (write_at_offset(buffers[head], sb.st_blksize, wfd, (off64_t)sb.st_blksize * block) != 0) {
+                return -1;
+            }
+        }
+        head = (head + 1) % WINDOW_SIZE;
+        ++head_block;
+    }
+
+    fprintf(mapf, "%d\n", range_used);
+    for (i = 0; i < range_used; ++i) {
+        fprintf(mapf, "%d %d\n", ranges[i*2], ranges[i*2+1]);
+    }
+
+    fclose(mapf);
+    close(fd);
+    if (encrypted) {
+        close(wfd);
+    }
+
+    return 0;
+}
+
+void reboot_to_recovery() {
+    property_set("sys.powerctl", "reboot,recovery");
+    sleep(10);
+}
+
+int main(int argc, char** argv)
+{
+    const char* input_path;
+    const char* map_file;
+    int do_reboot = 1;
+
+    if (argc != 1 && argc != 3) {
+        fprintf(stderr, "usage: %s [<transform_path> <map_file>]\n", argv[0]);
+        return 2;
+    }
+
+    if (argc == 3) {
+        // when command-line args are given this binary is being used
+        // for debugging; don't reboot to recovery at the end.
+        input_path = argv[1];
+        map_file = argv[2];
+        do_reboot = 0;
+    } else {
+        input_path = parse_recovery_command_file();
+        if (input_path == NULL) {
+            // if we're rebooting to recovery without a package (say,
+            // to wipe data), then we don't need to do anything before
+            // going to recovery.
+            fprintf(stderr, "no recovery command file or no update package arg");
+            reboot_to_recovery();
+            return 1;
+        }
+        map_file = CACHE_BLOCK_MAP;
+    }
+
+    // Turn the name of the file we're supposed to convert into an
+    // absolute path, so we can find what filesystem it's on.
+    char path[PATH_MAX+1];
+    if (realpath(input_path, path) == NULL) {
+        fprintf(stderr, "failed to convert %s to absolute path: %s\n", input_path, strerror(errno));
+        return 1;
+    }
+
+    int encryptable;
+    int encrypted;
+    const char* blk_dev = find_block_device(path, &encryptable, &encrypted);
+    if (blk_dev == NULL) {
+        fprintf(stderr, "failed to find block device for %s\n", path);
+        return 1;
+    }
+
+    // If the filesystem it's on isn't encrypted, we only produce the
+    // block map, we don't rewrite the file contents (it would be
+    // pointless to do so).
+    printf("encryptable: %s\n", encryptable ? "yes" : "no");
+    printf("  encrypted: %s\n", encrypted ? "yes" : "no");
+
+    if (!encryptable) {
+        // If the file is on a filesystem that doesn't support
+        // encryption (eg, /cache), then leave it alone.
+        //
+        // TODO: change this to be !encrypted -- if the file is on
+        // /data but /data isn't encrypted, we don't need to use the
+        // block map mechanism.  We do for now so as to get more
+        // testing of it (since most dogfood devices aren't
+        // encrypted).
+
+        unlink(RECOVERY_COMMAND_FILE_TMP);
+    } else {
+        if (produce_block_map(path, map_file, blk_dev, encrypted) != 0) {
+            return 1;
+        }
+    }
+
+    rename(RECOVERY_COMMAND_FILE_TMP, RECOVERY_COMMAND_FILE);
+    reboot_to_recovery();
+    return 0;
+}