1/* 2** 3** Copyright 2010, The Android Open Source Project 4** 5** Licensed under the Apache License, Version 2.0 (the "License"); 6** you may not use this file except in compliance with the License. 7** You may obtain a copy of the License at 8** 9** http://www.apache.org/licenses/LICENSE-2.0 10** 11** Unless required by applicable law or agreed to in writing, software 12** distributed under the License is distributed on an "AS IS" BASIS, 13** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 14** See the License for the specific language governing permissions and 15** limitations under the License. 16*/ 17#include <errno.h> 18#include <fcntl.h> 19#include <stdio.h> 20#include <string.h> 21#include <sys/mman.h> 22#include <sys/stat.h> 23#include <unistd.h> 24 25#include <private/android_filesystem_config.h> 26#include "package.h" 27 28/* 29 * WARNING WARNING WARNING WARNING 30 * 31 * The following code runs as root on production devices, before 32 * the run-as command has dropped the uid/gid. Hence be very 33 * conservative and keep in mind the following: 34 * 35 * - Performance does not matter here, clarity and safety of the code 36 * does however. Documentation is a must. 37 * 38 * - Avoid calling C library functions with complex implementations 39 * like malloc() and printf(). You want to depend on simple system 40 * calls instead, which behaviour is not going to be altered in 41 * unpredictible ways by environment variables or system properties. 42 * 43 * - Do not trust user input and/or the filesystem whenever possible. 44 * 45 */ 46 47/* The file containing the list of installed packages on the system */ 48#define PACKAGES_LIST_FILE "/data/system/packages.list" 49 50/* Copy 'srclen' string bytes from 'src' into buffer 'dst' of size 'dstlen' 51 * This function always zero-terminate the destination buffer unless 52 * 'dstlen' is 0, even in case of overflow. 53 * Returns a pointer into the src string, leaving off where the copy 54 * has stopped. The copy will stop when dstlen, srclen or a null 55 * character on src has been reached. 56 */ 57static const char* 58string_copy(char* dst, size_t dstlen, const char* src, size_t srclen) 59{ 60 const char* srcend = src + srclen; 61 const char* dstend = dst + dstlen; 62 63 if (dstlen == 0) 64 return src; 65 66 dstend--; /* make room for terminating zero */ 67 68 while (dst < dstend && src < srcend && *src != '\0') 69 *dst++ = *src++; 70 71 *dst = '\0'; /* zero-terminate result */ 72 return src; 73} 74 75/* Open 'filename' and map it into our address-space. 76 * Returns buffer address, or NULL on error 77 * On exit, *filesize will be set to the file's size, or 0 on error 78 */ 79static void* 80map_file(const char* filename, size_t* filesize) 81{ 82 int fd, ret, old_errno; 83 struct stat st; 84 size_t length = 0; 85 void* address = NULL; 86 gid_t oldegid; 87 88 *filesize = 0; 89 90 /* 91 * Temporarily switch effective GID to allow us to read 92 * the packages file 93 */ 94 95 oldegid = getegid(); 96 if (setegid(AID_PACKAGE_INFO) < 0) { 97 return NULL; 98 } 99 100 /* open the file for reading */ 101 fd = TEMP_FAILURE_RETRY(open(filename, O_RDONLY)); 102 if (fd < 0) { 103 return NULL; 104 } 105 106 /* restore back to our old egid */ 107 if (setegid(oldegid) < 0) { 108 goto EXIT; 109 } 110 111 /* get its size */ 112 ret = TEMP_FAILURE_RETRY(fstat(fd, &st)); 113 if (ret < 0) 114 goto EXIT; 115 116 /* Ensure that the file is owned by the system user */ 117 if ((st.st_uid != AID_SYSTEM) || (st.st_gid != AID_PACKAGE_INFO)) { 118 goto EXIT; 119 } 120 121 /* Ensure that the file has sane permissions */ 122 if ((st.st_mode & S_IWOTH) != 0) { 123 goto EXIT; 124 } 125 126 /* Ensure that the size is not ridiculously large */ 127 length = (size_t)st.st_size; 128 if ((off_t)length != st.st_size) { 129 errno = ENOMEM; 130 goto EXIT; 131 } 132 133 /* Memory-map the file now */ 134 do { 135 address = mmap(NULL, length, PROT_READ, MAP_PRIVATE, fd, 0); 136 } while (address == MAP_FAILED && errno == EINTR); 137 if (address == MAP_FAILED) { 138 address = NULL; 139 goto EXIT; 140 } 141 142 /* We're good, return size */ 143 *filesize = length; 144 145EXIT: 146 /* close the file, preserve old errno for better diagnostics */ 147 old_errno = errno; 148 close(fd); 149 errno = old_errno; 150 151 return address; 152} 153 154/* unmap the file, but preserve errno */ 155static void 156unmap_file(void* address, size_t size) 157{ 158 int old_errno = errno; 159 TEMP_FAILURE_RETRY(munmap(address, size)); 160 errno = old_errno; 161} 162 163/* Check that a given directory: 164 * - exists 165 * - is owned by a given uid/gid 166 * - is a real directory, not a symlink 167 * - isn't readable or writable by others 168 * 169 * Return 0 on success, or -1 on error. 170 * errno is set to EINVAL in case of failed check. 171 */ 172static int 173check_directory_ownership(const char* path, uid_t uid) 174{ 175 int ret; 176 struct stat st; 177 178 do { 179 ret = lstat(path, &st); 180 } while (ret < 0 && errno == EINTR); 181 182 if (ret < 0) 183 return -1; 184 185 /* /data/user/0 is a known safe symlink */ 186 if (strcmp("/data/user/0", path) == 0) 187 return 0; 188 189 /* must be a real directory, not a symlink */ 190 if (!S_ISDIR(st.st_mode)) 191 goto BAD; 192 193 /* must be owned by specific uid/gid */ 194 if (st.st_uid != uid || st.st_gid != uid) 195 goto BAD; 196 197 /* must not be readable or writable by others */ 198 if ((st.st_mode & (S_IROTH|S_IWOTH)) != 0) 199 goto BAD; 200 201 /* everything ok */ 202 return 0; 203 204BAD: 205 errno = EINVAL; 206 return -1; 207} 208 209/* This function is used to check the data directory path for safety. 210 * We check that every sub-directory is owned by the 'system' user 211 * and exists and is not a symlink. We also check that the full directory 212 * path is properly owned by the user ID. 213 * 214 * Return 0 on success, -1 on error. 215 */ 216int 217check_data_path(const char* dataPath, uid_t uid) 218{ 219 int nn; 220 221 /* the path should be absolute */ 222 if (dataPath[0] != '/') { 223 errno = EINVAL; 224 return -1; 225 } 226 227 /* look for all sub-paths, we do that by finding 228 * directory separators in the input path and 229 * checking each sub-path independently 230 */ 231 for (nn = 1; dataPath[nn] != '\0'; nn++) 232 { 233 char subpath[PATH_MAX]; 234 235 /* skip non-separator characters */ 236 if (dataPath[nn] != '/') 237 continue; 238 239 /* handle trailing separator case */ 240 if (dataPath[nn+1] == '\0') { 241 break; 242 } 243 244 /* found a separator, check that dataPath is not too long. */ 245 if (nn >= (int)(sizeof subpath)) { 246 errno = EINVAL; 247 return -1; 248 } 249 250 /* reject any '..' subpath */ 251 if (nn >= 3 && 252 dataPath[nn-3] == '/' && 253 dataPath[nn-2] == '.' && 254 dataPath[nn-1] == '.') { 255 errno = EINVAL; 256 return -1; 257 } 258 259 /* copy to 'subpath', then check ownership */ 260 memcpy(subpath, dataPath, nn); 261 subpath[nn] = '\0'; 262 263 if (check_directory_ownership(subpath, AID_SYSTEM) < 0) 264 return -1; 265 } 266 267 /* All sub-paths were checked, now verify that the full data 268 * directory is owned by the application uid 269 */ 270 if (check_directory_ownership(dataPath, uid) < 0) 271 return -1; 272 273 /* all clear */ 274 return 0; 275} 276 277/* Return TRUE iff a character is a space or tab */ 278static inline int 279is_space(char c) 280{ 281 return (c == ' ' || c == '\t'); 282} 283 284/* Skip any space or tab character from 'p' until 'end' is reached. 285 * Return new position. 286 */ 287static const char* 288skip_spaces(const char* p, const char* end) 289{ 290 while (p < end && is_space(*p)) 291 p++; 292 293 return p; 294} 295 296/* Skip any non-space and non-tab character from 'p' until 'end'. 297 * Return new position. 298 */ 299static const char* 300skip_non_spaces(const char* p, const char* end) 301{ 302 while (p < end && !is_space(*p)) 303 p++; 304 305 return p; 306} 307 308/* Find the first occurence of 'ch' between 'p' and 'end' 309 * Return its position, or 'end' if none is found. 310 */ 311static const char* 312find_first(const char* p, const char* end, char ch) 313{ 314 while (p < end && *p != ch) 315 p++; 316 317 return p; 318} 319 320/* Check that the non-space string starting at 'p' and eventually 321 * ending at 'end' equals 'name'. Return new position (after name) 322 * on success, or NULL on failure. 323 * 324 * This function fails is 'name' is NULL, empty or contains any space. 325 */ 326static const char* 327compare_name(const char* p, const char* end, const char* name) 328{ 329 /* 'name' must not be NULL or empty */ 330 if (name == NULL || name[0] == '\0' || p == end) 331 return NULL; 332 333 /* compare characters to those in 'name', excluding spaces */ 334 while (*name) { 335 /* note, we don't check for *p == '\0' since 336 * it will be caught in the next conditional. 337 */ 338 if (p >= end || is_space(*p)) 339 goto BAD; 340 341 if (*p != *name) 342 goto BAD; 343 344 p++; 345 name++; 346 } 347 348 /* must be followed by end of line or space */ 349 if (p < end && !is_space(*p)) 350 goto BAD; 351 352 return p; 353 354BAD: 355 return NULL; 356} 357 358/* Parse one or more whitespace characters starting from '*pp' 359 * until 'end' is reached. Updates '*pp' on exit. 360 * 361 * Return 0 on success, -1 on failure. 362 */ 363static int 364parse_spaces(const char** pp, const char* end) 365{ 366 const char* p = *pp; 367 368 if (p >= end || !is_space(*p)) { 369 errno = EINVAL; 370 return -1; 371 } 372 p = skip_spaces(p, end); 373 *pp = p; 374 return 0; 375} 376 377/* Parse a positive decimal number starting from '*pp' until 'end' 378 * is reached. Adjust '*pp' on exit. Return decimal value or -1 379 * in case of error. 380 * 381 * If the value is larger than INT_MAX, -1 will be returned, 382 * and errno set to EOVERFLOW. 383 * 384 * If '*pp' does not start with a decimal digit, -1 is returned 385 * and errno set to EINVAL. 386 */ 387static int 388parse_positive_decimal(const char** pp, const char* end) 389{ 390 const char* p = *pp; 391 int value = 0; 392 int overflow = 0; 393 394 if (p >= end || *p < '0' || *p > '9') { 395 errno = EINVAL; 396 return -1; 397 } 398 399 while (p < end) { 400 int ch = *p; 401 unsigned d = (unsigned)(ch - '0'); 402 int val2; 403 404 if (d >= 10U) /* d is unsigned, no lower bound check */ 405 break; 406 407 val2 = value*10 + (int)d; 408 if (val2 < value) 409 overflow = 1; 410 value = val2; 411 p++; 412 } 413 *pp = p; 414 415 if (overflow) { 416 errno = EOVERFLOW; 417 value = -1; 418 } 419 return value; 420} 421 422/* Read the system's package database and extract information about 423 * 'pkgname'. Return 0 in case of success, or -1 in case of error. 424 * 425 * If the package is unknown, return -1 and set errno to ENOENT 426 * If the package database is corrupted, return -1 and set errno to EINVAL 427 */ 428int 429get_package_info(const char* pkgName, uid_t userId, PackageInfo *info) 430{ 431 char* buffer; 432 size_t buffer_len; 433 const char* p; 434 const char* buffer_end; 435 int result = -1; 436 437 info->uid = 0; 438 info->isDebuggable = 0; 439 info->dataDir[0] = '\0'; 440 info->seinfo[0] = '\0'; 441 442 buffer = map_file(PACKAGES_LIST_FILE, &buffer_len); 443 if (buffer == NULL) 444 return -1; 445 446 p = buffer; 447 buffer_end = buffer + buffer_len; 448 449 /* expect the following format on each line of the control file: 450 * 451 * <pkgName> <uid> <debugFlag> <dataDir> <seinfo> 452 * 453 * where: 454 * <pkgName> is the package's name 455 * <uid> is the application-specific user Id (decimal) 456 * <debugFlag> is 1 if the package is debuggable, or 0 otherwise 457 * <dataDir> is the path to the package's data directory (e.g. /data/data/com.example.foo) 458 * <seinfo> is the seinfo label associated with the package 459 * 460 * The file is generated in com.android.server.PackageManagerService.Settings.writeLP() 461 */ 462 463 while (p < buffer_end) { 464 /* find end of current line and start of next one */ 465 const char* end = find_first(p, buffer_end, '\n'); 466 const char* next = (end < buffer_end) ? end + 1 : buffer_end; 467 const char* q; 468 int uid, debugFlag; 469 470 /* first field is the package name */ 471 p = compare_name(p, end, pkgName); 472 if (p == NULL) 473 goto NEXT_LINE; 474 475 /* skip spaces */ 476 if (parse_spaces(&p, end) < 0) 477 goto BAD_FORMAT; 478 479 /* second field is the pid */ 480 uid = parse_positive_decimal(&p, end); 481 if (uid < 0) 482 return -1; 483 484 info->uid = (uid_t) uid; 485 486 /* skip spaces */ 487 if (parse_spaces(&p, end) < 0) 488 goto BAD_FORMAT; 489 490 /* third field is debug flag (0 or 1) */ 491 debugFlag = parse_positive_decimal(&p, end); 492 switch (debugFlag) { 493 case 0: 494 info->isDebuggable = 0; 495 break; 496 case 1: 497 info->isDebuggable = 1; 498 break; 499 default: 500 goto BAD_FORMAT; 501 } 502 503 /* skip spaces */ 504 if (parse_spaces(&p, end) < 0) 505 goto BAD_FORMAT; 506 507 /* fourth field is data directory path and must not contain 508 * spaces. 509 */ 510 q = skip_non_spaces(p, end); 511 if (q == p) 512 goto BAD_FORMAT; 513 514 /* If userId == 0 (i.e. user is device owner) we can use dataDir value 515 * from packages.list, otherwise compose data directory as 516 * /data/user/$uid/$packageId 517 */ 518 if (userId == 0) { 519 p = string_copy(info->dataDir, sizeof info->dataDir, p, q - p); 520 } else { 521 snprintf(info->dataDir, 522 sizeof info->dataDir, 523 "/data/user/%d/%s", 524 userId, 525 pkgName); 526 p = q; 527 } 528 529 /* skip spaces */ 530 if (parse_spaces(&p, end) < 0) 531 goto BAD_FORMAT; 532 533 /* fifth field is the seinfo string */ 534 q = skip_non_spaces(p, end); 535 if (q == p) 536 goto BAD_FORMAT; 537 538 string_copy(info->seinfo, sizeof info->seinfo, p, q - p); 539 540 /* Ignore the rest */ 541 result = 0; 542 goto EXIT; 543 544 NEXT_LINE: 545 p = next; 546 } 547 548 /* the package is unknown */ 549 errno = ENOENT; 550 result = -1; 551 goto EXIT; 552 553BAD_FORMAT: 554 errno = EINVAL; 555 result = -1; 556 557EXIT: 558 unmap_file(buffer, buffer_len); 559 return result; 560} 561