/*
* 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 module creates a special filesystem containing two files.
//
// "/sideload/package.zip" appears to be a normal file, but reading
// from it causes data to be fetched from the adb host. We can use
// this to sideload packages over an adb connection without having to
// store the entire package in RAM on the device.
//
// Because we may not trust the adb host, this filesystem maintains
// the following invariant: each read of a given position returns the
// same data as the first read at that position. That is, once a
// section of the file is read, future reads of that section return
// the same data. (Otherwise, a malicious adb host process could
// return one set of bits when the package is read for signature
// verification, and then different bits for when the package is
// accessed by the installer.) If the adb host returns something
// different than it did on the first read, the reader of the file
// will see their read fail with EINVAL.
//
// The other file, "/sideload/exit", is used to control the subprocess
// that creates this filesystem. Calling stat() on the exit file
// causes the filesystem to be unmounted and the adb process on the
// device shut down.
//
// Note that only the minimal set of file operations needed for these
// two files is implemented. In particular, you can't opendir() or
// readdir() on the "/sideload" directory; ls on it won't work.
#include <ctype.h>
#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <linux/fuse.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/inotify.h>
#include <sys/mount.h>
#include <sys/resource.h>
#include <sys/stat.h>
#include <sys/statfs.h>
#include <sys/time.h>
#include <sys/uio.h>
#include <unistd.h>
#include "mincrypt/sha256.h"
#include "fuse_sideload.h"
#define PACKAGE_FILE_ID (FUSE_ROOT_ID+1)
#define EXIT_FLAG_ID (FUSE_ROOT_ID+2)
#define NO_STATUS 1
#define NO_STATUS_EXIT 2
struct fuse_data {
int ffd; // file descriptor for the fuse socket
struct provider_vtab* vtab;
void* cookie;
uint64_t file_size; // bytes
uint32_t block_size; // block size that the adb host is using to send the file to us
uint32_t file_blocks; // file size in block_size blocks
uid_t uid;
gid_t gid;
uint32_t curr_block; // cache the block most recently read from the host
uint8_t* block_data;
uint8_t* extra_block; // another block of storage for reads that
// span two blocks
uint8_t* hashes; // SHA-256 hash of each block (all zeros
// if block hasn't been read yet)
};
static void fuse_reply(struct fuse_data* fd, __u64 unique, const void *data, size_t len)
{
struct fuse_out_header hdr;
struct iovec vec[2];
int res;
hdr.len = len + sizeof(hdr);
hdr.error = 0;
hdr.unique = unique;
vec[0].iov_base = &hdr;
vec[0].iov_len = sizeof(hdr);
vec[1].iov_base = data;
vec[1].iov_len = len;
res = writev(fd->ffd, vec, 2);
if (res < 0) {
printf("*** REPLY FAILED *** %d\n", errno);
}
}
static int handle_init(void* data, struct fuse_data* fd, const struct fuse_in_header* hdr) {
const struct fuse_init_in* req = data;
struct fuse_init_out out;
out.major = FUSE_KERNEL_VERSION;
out.minor = FUSE_KERNEL_MINOR_VERSION;
out.max_readahead = req->max_readahead;
out.flags = 0;
out.max_background = 32;
out.congestion_threshold = 32;
out.max_write = 4096;
fuse_reply(fd, hdr->unique, &out, sizeof(out));
return NO_STATUS;
}
static void fill_attr(struct fuse_attr* attr, struct fuse_data* fd,
uint64_t nodeid, uint64_t size, uint32_t mode) {
memset(attr, 0, sizeof(*attr));
attr->nlink = 1;
attr->uid = fd->uid;
attr->gid = fd->gid;
attr->blksize = 4096;
attr->ino = nodeid;
attr->size = size;
attr->blocks = (size == 0) ? 0 : (((size-1) / attr->blksize) + 1);
attr->mode = mode;
}
static int handle_getattr(void* data, struct fuse_data* fd, const struct fuse_in_header* hdr) {
const struct fuse_getattr_in* req = data;
struct fuse_attr_out out;
memset(&out, 0, sizeof(out));
out.attr_valid = 10;
if (hdr->nodeid == FUSE_ROOT_ID) {
fill_attr(&(out.attr), fd, hdr->nodeid, 4096, S_IFDIR | 0555);
} else if (hdr->nodeid == PACKAGE_FILE_ID) {
fill_attr(&(out.attr), fd, PACKAGE_FILE_ID, fd->file_size, S_IFREG | 0444);
} else if (hdr->nodeid == EXIT_FLAG_ID) {
fill_attr(&(out.attr), fd, EXIT_FLAG_ID, 0, S_IFREG | 0);
} else {
return -ENOENT;
}
fuse_reply(fd, hdr->unique, &out, sizeof(out));
return (hdr->nodeid == EXIT_FLAG_ID) ? NO_STATUS_EXIT : NO_STATUS;
}
static int handle_lookup(void* data, struct fuse_data* fd,
const struct fuse_in_header* hdr) {
struct fuse_entry_out out;
memset(&out, 0, sizeof(out));
out.entry_valid = 10;
out.attr_valid = 10;
if (strncmp(FUSE_SIDELOAD_HOST_FILENAME, data,
sizeof(FUSE_SIDELOAD_HOST_FILENAME)) == 0) {
out.nodeid = PACKAGE_FILE_ID;
out.generation = PACKAGE_FILE_ID;
fill_attr(&(out.attr), fd, PACKAGE_FILE_ID, fd->file_size, S_IFREG | 0444);
} else if (strncmp(FUSE_SIDELOAD_HOST_EXIT_FLAG, data,
sizeof(FUSE_SIDELOAD_HOST_EXIT_FLAG)) == 0) {
out.nodeid = EXIT_FLAG_ID;
out.generation = EXIT_FLAG_ID;
fill_attr(&(out.attr), fd, EXIT_FLAG_ID, 0, S_IFREG | 0);
} else {
return -ENOENT;
}
fuse_reply(fd, hdr->unique, &out, sizeof(out));
return (out.nodeid == EXIT_FLAG_ID) ? NO_STATUS_EXIT : NO_STATUS;
}
static int handle_open(void* data, struct fuse_data* fd, const struct fuse_in_header* hdr) {
const struct fuse_open_in* req = data;
if (hdr->nodeid == EXIT_FLAG_ID) return -EPERM;
if (hdr->nodeid != PACKAGE_FILE_ID) return -ENOENT;
struct fuse_open_out out;
memset(&out, 0, sizeof(out));
out.fh = 10; // an arbitrary number; we always use the same handle
fuse_reply(fd, hdr->unique, &out, sizeof(out));
return NO_STATUS;
}
static int handle_flush(void* data, struct fuse_data* fd, const struct fuse_in_header* hdr) {
return 0;
}
static int handle_release(void* data, struct fuse_data* fd, const struct fuse_in_header* hdr) {
return 0;
}
// Fetch a block from the host into fd->curr_block and fd->block_data.
// Returns 0 on successful fetch, negative otherwise.
static int fetch_block(struct fuse_data* fd, uint32_t block) {
if (block == fd->curr_block) {
return 0;
}
if (block >= fd->file_blocks) {
memset(fd->block_data, 0, fd->block_size);
fd->curr_block = block;
return 0;
}
size_t fetch_size = fd->block_size;
if (block * fd->block_size + fetch_size > fd->file_size) {
// If we're reading the last (partial) block of the file,
// expect a shorter response from the host, and pad the rest
// of the block with zeroes.
fetch_size = fd->file_size - (block * fd->block_size);
memset(fd->block_data + fetch_size, 0, fd->block_size - fetch_size);
}
int result = fd->vtab->read_block(fd->cookie, block, fd->block_data, fetch_size);
if (result < 0) return result;
fd->curr_block = block;
// Verify the hash of the block we just got from the host.
//
// - If the hash of the just-received data matches the stored hash
// for the block, accept it.
// - If the stored hash is all zeroes, store the new hash and
// accept the block (this is the first time we've read this
// block).
// - Otherwise, return -EINVAL for the read.
uint8_t hash[SHA256_DIGEST_SIZE];
SHA256_hash(fd->block_data, fd->block_size, hash);
uint8_t* blockhash = fd->hashes + block * SHA256_DIGEST_SIZE;
if (memcmp(hash, blockhash, SHA256_DIGEST_SIZE) == 0) {
return 0;
}
int i;
for (i = 0; i < SHA256_DIGEST_SIZE; ++i) {
if (blockhash[i] != 0) {
fd->curr_block = -1;
return -EIO;
}
}
memcpy(blockhash, hash, SHA256_DIGEST_SIZE);
return 0;
}
static int handle_read(void* data, struct fuse_data* fd, const struct fuse_in_header* hdr) {
const struct fuse_read_in* req = data;
struct fuse_out_header outhdr;
struct iovec vec[3];
int vec_used;
int result;
if (hdr->nodeid != PACKAGE_FILE_ID) return -ENOENT;
uint64_t offset = req->offset;
uint32_t size = req->size;
// The docs on the fuse kernel interface are vague about what to
// do when a read request extends past the end of the file. We
// can return a short read -- the return structure does include a
// length field -- but in testing that caused the program using
// the file to segfault. (I speculate that this is due to the
// reading program accessing it via mmap; maybe mmap dislikes when
// you return something short of a whole page?) To fix this we
// zero-pad reads that extend past the end of the file so we're
// always returning exactly as many bytes as were requested.
// (Users of the mapped file have to know its real length anyway.)
outhdr.len = sizeof(outhdr) + size;
outhdr.error = 0;
outhdr.unique = hdr->unique;
vec[0].iov_base = &outhdr;
vec[0].iov_len = sizeof(outhdr);
uint32_t block = offset / fd->block_size;
result = fetch_block(fd, block);
if (result != 0) return result;
// Two cases:
//
// - the read request is entirely within this block. In this
// case we can reply immediately.
//
// - the read request goes over into the next block. Note that
// since we mount the filesystem with max_read=block_size, a
// read can never span more than two blocks. In this case we
// copy the block to extra_block and issue a fetch for the
// following block.
uint32_t block_offset = offset - (block * fd->block_size);
if (size + block_offset <= fd->block_size) {
// First case: the read fits entirely in the first block.
vec[1].iov_base = fd->block_data + block_offset;
vec[1].iov_len = size;
vec_used = 2;
} else {
// Second case: the read spills over into the next block.
memcpy(fd->extra_block, fd->block_data + block_offset,
fd->block_size - block_offset);
vec[1].iov_base = fd->extra_block;
vec[1].iov_len = fd->block_size - block_offset;
result = fetch_block(fd, block+1);
if (result != 0) return result;
vec[2].iov_base = fd->block_data;
vec[2].iov_len = size - vec[1].iov_len;
vec_used = 3;
}
if (writev(fd->ffd, vec, vec_used) < 0) {
printf("*** READ REPLY FAILED: %s ***\n", strerror(errno));
}
return NO_STATUS;
}
int run_fuse_sideload(struct provider_vtab* vtab, void* cookie,
uint64_t file_size, uint32_t block_size)
{
int result;
// If something's already mounted on our mountpoint, try to remove
// it. (Mostly in case of a previous abnormal exit.)
umount2(FUSE_SIDELOAD_HOST_MOUNTPOINT, MNT_FORCE);
if (block_size < 1024) {
fprintf(stderr, "block size (%u) is too small\n", block_size);
return -1;
}
if (block_size > (1<<22)) { // 4 MiB
fprintf(stderr, "block size (%u) is too large\n", block_size);
return -1;
}
struct fuse_data fd;
memset(&fd, 0, sizeof(fd));
fd.vtab = vtab;
fd.cookie = cookie;
fd.file_size = file_size;
fd.block_size = block_size;
fd.file_blocks = (file_size == 0) ? 0 : (((file_size-1) / block_size) + 1);
if (fd.file_blocks > (1<<18)) {
fprintf(stderr, "file has too many blocks (%u)\n", fd.file_blocks);
result = -1;
goto done;
}
fd.hashes = (uint8_t*)calloc(fd.file_blocks, SHA256_DIGEST_SIZE);
if (fd.hashes == NULL) {
fprintf(stderr, "failed to allocate %d bites for hashes\n",
fd.file_blocks * SHA256_DIGEST_SIZE);
result = -1;
goto done;
}
fd.uid = getuid();
fd.gid = getgid();
fd.curr_block = -1;
fd.block_data = (uint8_t*)malloc(block_size);
if (fd.block_data == NULL) {
fprintf(stderr, "failed to allocate %d bites for block_data\n", block_size);
result = -1;
goto done;
}
fd.extra_block = (uint8_t*)malloc(block_size);
if (fd.extra_block == NULL) {
fprintf(stderr, "failed to allocate %d bites for extra_block\n", block_size);
result = -1;
goto done;
}
fd.ffd = open("/dev/fuse", O_RDWR);
if (fd.ffd < 0) {
perror("open /dev/fuse");
result = -1;
goto done;
}
char opts[256];
snprintf(opts, sizeof(opts),
("fd=%d,user_id=%d,group_id=%d,max_read=%zu,"
"allow_other,rootmode=040000"),
fd.ffd, fd.uid, fd.gid, block_size);
result = mount("/dev/fuse", FUSE_SIDELOAD_HOST_MOUNTPOINT,
"fuse", MS_NOSUID | MS_NODEV | MS_RDONLY | MS_NOEXEC, opts);
if (result < 0) {
perror("mount");
goto done;
}
uint8_t request_buffer[sizeof(struct fuse_in_header) + PATH_MAX*8];
for (;;) {
ssize_t len = read(fd.ffd, request_buffer, sizeof(request_buffer));
if (len < 0) {
if (errno != EINTR) {
perror("read request");
if (errno == ENODEV) {
result = -1;
break;
}
}
continue;
}
if ((size_t)len < sizeof(struct fuse_in_header)) {
fprintf(stderr, "request too short: len=%zu\n", (size_t)len);
continue;
}
struct fuse_in_header* hdr = (struct fuse_in_header*) request_buffer;
void* data = request_buffer + sizeof(struct fuse_in_header);
result = -ENOSYS;
switch (hdr->opcode) {
case FUSE_INIT:
result = handle_init(data, &fd, hdr);
break;
case FUSE_LOOKUP:
result = handle_lookup(data, &fd, hdr);
break;
case FUSE_GETATTR:
result = handle_getattr(data, &fd, hdr);
break;
case FUSE_OPEN:
result = handle_open(data, &fd, hdr);
break;
case FUSE_READ:
result = handle_read(data, &fd, hdr);
break;
case FUSE_FLUSH:
result = handle_flush(data, &fd, hdr);
break;
case FUSE_RELEASE:
result = handle_release(data, &fd, hdr);
break;
default:
fprintf(stderr, "unknown fuse request opcode %d\n", hdr->opcode);
break;
}
if (result == NO_STATUS_EXIT) {
result = 0;
break;
}
if (result != NO_STATUS) {
struct fuse_out_header outhdr;
outhdr.len = sizeof(outhdr);
outhdr.error = result;
outhdr.unique = hdr->unique;
write(fd.ffd, &outhdr, sizeof(outhdr));
}
}
done:
fd.vtab->close(fd.cookie);
result = umount2(FUSE_SIDELOAD_HOST_MOUNTPOINT, MNT_DETACH);
if (result < 0) {
printf("fuse_sideload umount failed: %s\n", strerror(errno));
}
if (fd.ffd) close(fd.ffd);
free(fd.hashes);
free(fd.block_data);
free(fd.extra_block);
return result;
}