1 /*
2 * Copyright (C) 2014 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 // This module creates a special filesystem containing two files.
18 //
19 // "/sideload/package.zip" appears to be a normal file, but reading
20 // from it causes data to be fetched from the adb host. We can use
21 // this to sideload packages over an adb connection without having to
22 // store the entire package in RAM on the device.
23 //
24 // Because we may not trust the adb host, this filesystem maintains
25 // the following invariant: each read of a given position returns the
26 // same data as the first read at that position. That is, once a
27 // section of the file is read, future reads of that section return
28 // the same data. (Otherwise, a malicious adb host process could
29 // return one set of bits when the package is read for signature
30 // verification, and then different bits for when the package is
31 // accessed by the installer.) If the adb host returns something
32 // different than it did on the first read, the reader of the file
33 // will see their read fail with EINVAL.
34 //
35 // The other file, "/sideload/exit", is used to control the subprocess
36 // that creates this filesystem. Calling stat() on the exit file
37 // causes the filesystem to be unmounted and the adb process on the
38 // device shut down.
39 //
40 // Note that only the minimal set of file operations needed for these
41 // two files is implemented. In particular, you can't opendir() or
42 // readdir() on the "/sideload" directory; ls on it won't work.
43
44 #include "fuse_sideload.h"
45
46 #include <errno.h>
47 #include <fcntl.h>
48 #include <limits.h> // PATH_MAX
49 #include <linux/fuse.h>
50 #include <stdint.h>
51 #include <stdio.h>
52 #include <stdlib.h>
53 #include <string.h>
54 #include <sys/mount.h>
55 #include <sys/param.h> // MIN
56 #include <sys/stat.h>
57 #include <sys/uio.h>
58 #include <unistd.h>
59
60 #include <array>
61 #include <string>
62 #include <vector>
63
64 #include <android-base/stringprintf.h>
65 #include <android-base/unique_fd.h>
66 #include <openssl/sha.h>
67
68 static constexpr uint64_t PACKAGE_FILE_ID = FUSE_ROOT_ID + 1;
69 static constexpr uint64_t EXIT_FLAG_ID = FUSE_ROOT_ID + 2;
70
71 static constexpr int NO_STATUS = 1;
72 static constexpr int NO_STATUS_EXIT = 2;
73
74 using SHA256Digest = std::array<uint8_t, SHA256_DIGEST_LENGTH>;
75
76 struct fuse_data {
77 android::base::unique_fd ffd; // file descriptor for the fuse socket
78
79 provider_vtab vtab;
80
81 uint64_t file_size; // bytes
82
83 uint32_t block_size; // block size that the adb host is using to send the file to us
84 uint32_t file_blocks; // file size in block_size blocks
85
86 uid_t uid;
87 gid_t gid;
88
89 uint32_t curr_block; // cache the block most recently read from the host
90 uint8_t* block_data;
91
92 uint8_t* extra_block; // another block of storage for reads that span two blocks
93
94 std::vector<SHA256Digest>
95 hashes; // SHA-256 hash of each block (all zeros if block hasn't been read yet)
96 };
97
fuse_reply(const fuse_data * fd,uint64_t unique,const void * data,size_t len)98 static void fuse_reply(const fuse_data* fd, uint64_t unique, const void* data, size_t len) {
99 fuse_out_header hdr;
100 hdr.len = len + sizeof(hdr);
101 hdr.error = 0;
102 hdr.unique = unique;
103
104 struct iovec vec[2];
105 vec[0].iov_base = &hdr;
106 vec[0].iov_len = sizeof(hdr);
107 vec[1].iov_base = const_cast<void*>(data);
108 vec[1].iov_len = len;
109
110 int res = writev(fd->ffd, vec, 2);
111 if (res == -1) {
112 printf("*** REPLY FAILED *** %s\n", strerror(errno));
113 }
114 }
115
handle_init(void * data,fuse_data * fd,const fuse_in_header * hdr)116 static int handle_init(void* data, fuse_data* fd, const fuse_in_header* hdr) {
117 const fuse_init_in* req = static_cast<const fuse_init_in*>(data);
118
119 // Kernel 2.6.16 is the first stable kernel with struct fuse_init_out defined (fuse version 7.6).
120 // The structure is the same from 7.6 through 7.22. Beginning with 7.23, the structure increased
121 // in size and added new parameters.
122 if (req->major != FUSE_KERNEL_VERSION || req->minor < 6) {
123 printf("Fuse kernel version mismatch: Kernel version %d.%d, Expected at least %d.6", req->major,
124 req->minor, FUSE_KERNEL_VERSION);
125 return -1;
126 }
127
128 fuse_init_out out;
129 out.minor = MIN(req->minor, FUSE_KERNEL_MINOR_VERSION);
130 size_t fuse_struct_size = sizeof(out);
131 #if defined(FUSE_COMPAT_22_INIT_OUT_SIZE)
132 /* FUSE_KERNEL_VERSION >= 23. */
133
134 // If the kernel only works on minor revs older than or equal to 22, then use the older structure
135 // size since this code only uses the 7.22 version of the structure.
136 if (req->minor <= 22) {
137 fuse_struct_size = FUSE_COMPAT_22_INIT_OUT_SIZE;
138 }
139 #endif
140
141 out.major = FUSE_KERNEL_VERSION;
142 out.max_readahead = req->max_readahead;
143 out.flags = 0;
144 out.max_background = 32;
145 out.congestion_threshold = 32;
146 out.max_write = 4096;
147 fuse_reply(fd, hdr->unique, &out, fuse_struct_size);
148
149 return NO_STATUS;
150 }
151
fill_attr(fuse_attr * attr,const fuse_data * fd,uint64_t nodeid,uint64_t size,uint32_t mode)152 static void fill_attr(fuse_attr* attr, const fuse_data* fd, uint64_t nodeid, uint64_t size,
153 uint32_t mode) {
154 *attr = {};
155 attr->nlink = 1;
156 attr->uid = fd->uid;
157 attr->gid = fd->gid;
158 attr->blksize = 4096;
159
160 attr->ino = nodeid;
161 attr->size = size;
162 attr->blocks = (size == 0) ? 0 : (((size - 1) / attr->blksize) + 1);
163 attr->mode = mode;
164 }
165
handle_getattr(void *,const fuse_data * fd,const fuse_in_header * hdr)166 static int handle_getattr(void* /* data */, const fuse_data* fd, const fuse_in_header* hdr) {
167 fuse_attr_out out = {};
168 out.attr_valid = 10;
169
170 if (hdr->nodeid == FUSE_ROOT_ID) {
171 fill_attr(&(out.attr), fd, hdr->nodeid, 4096, S_IFDIR | 0555);
172 } else if (hdr->nodeid == PACKAGE_FILE_ID) {
173 fill_attr(&(out.attr), fd, PACKAGE_FILE_ID, fd->file_size, S_IFREG | 0444);
174 } else if (hdr->nodeid == EXIT_FLAG_ID) {
175 fill_attr(&(out.attr), fd, EXIT_FLAG_ID, 0, S_IFREG | 0);
176 } else {
177 return -ENOENT;
178 }
179
180 fuse_reply(fd, hdr->unique, &out, sizeof(out));
181 return (hdr->nodeid == EXIT_FLAG_ID) ? NO_STATUS_EXIT : NO_STATUS;
182 }
183
handle_lookup(void * data,const fuse_data * fd,const fuse_in_header * hdr)184 static int handle_lookup(void* data, const fuse_data* fd, const fuse_in_header* hdr) {
185 if (data == nullptr) return -ENOENT;
186
187 fuse_entry_out out = {};
188 out.entry_valid = 10;
189 out.attr_valid = 10;
190
191 std::string filename(static_cast<const char*>(data));
192 if (filename == FUSE_SIDELOAD_HOST_FILENAME) {
193 out.nodeid = PACKAGE_FILE_ID;
194 out.generation = PACKAGE_FILE_ID;
195 fill_attr(&(out.attr), fd, PACKAGE_FILE_ID, fd->file_size, S_IFREG | 0444);
196 } else if (filename == FUSE_SIDELOAD_HOST_EXIT_FLAG) {
197 out.nodeid = EXIT_FLAG_ID;
198 out.generation = EXIT_FLAG_ID;
199 fill_attr(&(out.attr), fd, EXIT_FLAG_ID, 0, S_IFREG | 0);
200 } else {
201 return -ENOENT;
202 }
203
204 fuse_reply(fd, hdr->unique, &out, sizeof(out));
205 return (out.nodeid == EXIT_FLAG_ID) ? NO_STATUS_EXIT : NO_STATUS;
206 }
207
handle_open(void *,const fuse_data * fd,const fuse_in_header * hdr)208 static int handle_open(void* /* data */, const fuse_data* fd, const fuse_in_header* hdr) {
209 if (hdr->nodeid == EXIT_FLAG_ID) return -EPERM;
210 if (hdr->nodeid != PACKAGE_FILE_ID) return -ENOENT;
211
212 fuse_open_out out = {};
213 out.fh = 10; // an arbitrary number; we always use the same handle
214 fuse_reply(fd, hdr->unique, &out, sizeof(out));
215 return NO_STATUS;
216 }
217
handle_flush(void *,fuse_data *,const fuse_in_header *)218 static int handle_flush(void* /* data */, fuse_data* /* fd */, const fuse_in_header* /* hdr */) {
219 return 0;
220 }
221
handle_release(void *,fuse_data *,const fuse_in_header *)222 static int handle_release(void* /* data */, fuse_data* /* fd */, const fuse_in_header* /* hdr */) {
223 return 0;
224 }
225
226 // Fetch a block from the host into fd->curr_block and fd->block_data.
227 // Returns 0 on successful fetch, negative otherwise.
fetch_block(fuse_data * fd,uint32_t block)228 static int fetch_block(fuse_data* fd, uint32_t block) {
229 if (block == fd->curr_block) {
230 return 0;
231 }
232
233 if (block >= fd->file_blocks) {
234 memset(fd->block_data, 0, fd->block_size);
235 fd->curr_block = block;
236 return 0;
237 }
238
239 size_t fetch_size = fd->block_size;
240 if (block * fd->block_size + fetch_size > fd->file_size) {
241 // If we're reading the last (partial) block of the file, expect a shorter response from the
242 // host, and pad the rest of the block with zeroes.
243 fetch_size = fd->file_size - (block * fd->block_size);
244 memset(fd->block_data + fetch_size, 0, fd->block_size - fetch_size);
245 }
246
247 int result = fd->vtab.read_block(block, fd->block_data, fetch_size);
248 if (result < 0) return result;
249
250 fd->curr_block = block;
251
252 // Verify the hash of the block we just got from the host.
253 //
254 // - If the hash of the just-received data matches the stored hash for the block, accept it.
255 // - If the stored hash is all zeroes, store the new hash and accept the block (this is the first
256 // time we've read this block).
257 // - Otherwise, return -EINVAL for the read.
258
259 SHA256Digest hash;
260 SHA256(fd->block_data, fd->block_size, hash.data());
261
262 const SHA256Digest& blockhash = fd->hashes[block];
263 if (hash == blockhash) {
264 return 0;
265 }
266
267 for (uint8_t i : blockhash) {
268 if (i != 0) {
269 fd->curr_block = -1;
270 return -EIO;
271 }
272 }
273
274 fd->hashes[block] = hash;
275 return 0;
276 }
277
handle_read(void * data,fuse_data * fd,const fuse_in_header * hdr)278 static int handle_read(void* data, fuse_data* fd, const fuse_in_header* hdr) {
279 if (hdr->nodeid != PACKAGE_FILE_ID) return -ENOENT;
280
281 const fuse_read_in* req = static_cast<const fuse_read_in*>(data);
282 uint64_t offset = req->offset;
283 uint32_t size = req->size;
284
285 // The docs on the fuse kernel interface are vague about what to do when a read request extends
286 // past the end of the file. We can return a short read -- the return structure does include a
287 // length field -- but in testing that caused the program using the file to segfault. (I
288 // speculate that this is due to the reading program accessing it via mmap; maybe mmap dislikes
289 // when you return something short of a whole page?) To fix this we zero-pad reads that extend
290 // past the end of the file so we're always returning exactly as many bytes as were requested.
291 // (Users of the mapped file have to know its real length anyway.)
292
293 fuse_out_header outhdr;
294 outhdr.len = sizeof(outhdr) + size;
295 outhdr.error = 0;
296 outhdr.unique = hdr->unique;
297
298 struct iovec vec[3];
299 vec[0].iov_base = &outhdr;
300 vec[0].iov_len = sizeof(outhdr);
301
302 uint32_t block = offset / fd->block_size;
303 int result = fetch_block(fd, block);
304 if (result != 0) return result;
305
306 // Two cases:
307 //
308 // - the read request is entirely within this block. In this case we can reply immediately.
309 //
310 // - the read request goes over into the next block. Note that since we mount the filesystem
311 // with max_read=block_size, a read can never span more than two blocks. In this case we copy
312 // the block to extra_block and issue a fetch for the following block.
313
314 uint32_t block_offset = offset - (block * fd->block_size);
315
316 int vec_used;
317 if (size + block_offset <= fd->block_size) {
318 // First case: the read fits entirely in the first block.
319
320 vec[1].iov_base = fd->block_data + block_offset;
321 vec[1].iov_len = size;
322 vec_used = 2;
323 } else {
324 // Second case: the read spills over into the next block.
325
326 memcpy(fd->extra_block, fd->block_data + block_offset, fd->block_size - block_offset);
327 vec[1].iov_base = fd->extra_block;
328 vec[1].iov_len = fd->block_size - block_offset;
329
330 result = fetch_block(fd, block + 1);
331 if (result != 0) return result;
332 vec[2].iov_base = fd->block_data;
333 vec[2].iov_len = size - vec[1].iov_len;
334 vec_used = 3;
335 }
336
337 if (writev(fd->ffd, vec, vec_used) == -1) {
338 printf("*** READ REPLY FAILED: %s ***\n", strerror(errno));
339 }
340 return NO_STATUS;
341 }
342
run_fuse_sideload(const provider_vtab & vtab,uint64_t file_size,uint32_t block_size,const char * mount_point)343 int run_fuse_sideload(const provider_vtab& vtab, uint64_t file_size, uint32_t block_size,
344 const char* mount_point) {
345 // If something's already mounted on our mountpoint, try to remove it. (Mostly in case of a
346 // previous abnormal exit.)
347 umount2(mount_point, MNT_FORCE);
348
349 // fs/fuse/inode.c in kernel code uses the greater of 4096 and the passed-in max_read.
350 if (block_size < 4096) {
351 fprintf(stderr, "block size (%u) is too small\n", block_size);
352 return -1;
353 }
354 if (block_size > (1 << 22)) { // 4 MiB
355 fprintf(stderr, "block size (%u) is too large\n", block_size);
356 return -1;
357 }
358
359 fuse_data fd = {};
360 fd.vtab = vtab;
361 fd.file_size = file_size;
362 fd.block_size = block_size;
363 fd.file_blocks = (file_size == 0) ? 0 : (((file_size - 1) / block_size) + 1);
364
365 int result;
366 if (fd.file_blocks > (1 << 18)) {
367 fprintf(stderr, "file has too many blocks (%u)\n", fd.file_blocks);
368 result = -1;
369 goto done;
370 }
371
372 // All hashes will be zero-initialized.
373 fd.hashes.resize(fd.file_blocks);
374 fd.uid = getuid();
375 fd.gid = getgid();
376
377 fd.curr_block = -1;
378 fd.block_data = static_cast<uint8_t*>(malloc(block_size));
379 if (fd.block_data == nullptr) {
380 fprintf(stderr, "failed to allocate %d bites for block_data\n", block_size);
381 result = -1;
382 goto done;
383 }
384 fd.extra_block = static_cast<uint8_t*>(malloc(block_size));
385 if (fd.extra_block == nullptr) {
386 fprintf(stderr, "failed to allocate %d bites for extra_block\n", block_size);
387 result = -1;
388 goto done;
389 }
390
391 fd.ffd.reset(open("/dev/fuse", O_RDWR));
392 if (!fd.ffd) {
393 perror("open /dev/fuse");
394 result = -1;
395 goto done;
396 }
397
398 {
399 std::string opts = android::base::StringPrintf(
400 "fd=%d,user_id=%d,group_id=%d,max_read=%u,allow_other,rootmode=040000", fd.ffd.get(),
401 fd.uid, fd.gid, block_size);
402
403 result = mount("/dev/fuse", mount_point, "fuse", MS_NOSUID | MS_NODEV | MS_RDONLY | MS_NOEXEC,
404 opts.c_str());
405 if (result == -1) {
406 perror("mount");
407 goto done;
408 }
409 }
410
411 uint8_t request_buffer[sizeof(fuse_in_header) + PATH_MAX * 8];
412 for (;;) {
413 ssize_t len = TEMP_FAILURE_RETRY(read(fd.ffd, request_buffer, sizeof(request_buffer)));
414 if (len == -1) {
415 perror("read request");
416 if (errno == ENODEV) {
417 result = -1;
418 break;
419 }
420 continue;
421 }
422
423 if (static_cast<size_t>(len) < sizeof(fuse_in_header)) {
424 fprintf(stderr, "request too short: len=%zd\n", len);
425 continue;
426 }
427
428 fuse_in_header* hdr = reinterpret_cast<fuse_in_header*>(request_buffer);
429 void* data = request_buffer + sizeof(fuse_in_header);
430
431 result = -ENOSYS;
432
433 switch (hdr->opcode) {
434 case FUSE_INIT:
435 result = handle_init(data, &fd, hdr);
436 break;
437
438 case FUSE_LOOKUP:
439 result = handle_lookup(data, &fd, hdr);
440 break;
441
442 case FUSE_GETATTR:
443 result = handle_getattr(data, &fd, hdr);
444 break;
445
446 case FUSE_OPEN:
447 result = handle_open(data, &fd, hdr);
448 break;
449
450 case FUSE_READ:
451 result = handle_read(data, &fd, hdr);
452 break;
453
454 case FUSE_FLUSH:
455 result = handle_flush(data, &fd, hdr);
456 break;
457
458 case FUSE_RELEASE:
459 result = handle_release(data, &fd, hdr);
460 break;
461
462 default:
463 fprintf(stderr, "unknown fuse request opcode %d\n", hdr->opcode);
464 break;
465 }
466
467 if (result == NO_STATUS_EXIT) {
468 result = 0;
469 break;
470 }
471
472 if (result != NO_STATUS) {
473 fuse_out_header outhdr;
474 outhdr.len = sizeof(outhdr);
475 outhdr.error = result;
476 outhdr.unique = hdr->unique;
477 TEMP_FAILURE_RETRY(write(fd.ffd, &outhdr, sizeof(outhdr)));
478 }
479 }
480
481 done:
482 fd.vtab.close();
483
484 if (umount2(mount_point, MNT_DETACH) == -1) {
485 fprintf(stderr, "fuse_sideload umount failed: %s\n", strerror(errno));
486 }
487
488 free(fd.block_data);
489 free(fd.extra_block);
490
491 return result;
492 }
493