com_android_internal_os_Zygote.cpp revision 0161bbc6e54744d5e0348af3d123858818f966e9
1/* 2 * Copyright (C) 2008 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#define LOG_TAG "Zygote" 18 19// sys/mount.h has to come before linux/fs.h due to redefinition of MS_RDONLY, MS_BIND, etc 20#include <sys/mount.h> 21#include <linux/fs.h> 22 23#include <grp.h> 24#include <fcntl.h> 25#include <paths.h> 26#include <signal.h> 27#include <stdlib.h> 28#include <unistd.h> 29#include <sys/capability.h> 30#include <sys/personality.h> 31#include <sys/prctl.h> 32#include <sys/resource.h> 33#include <sys/stat.h> 34#include <sys/types.h> 35#include <sys/utsname.h> 36#include <sys/wait.h> 37 38 39#include <cutils/fs.h> 40#include <cutils/multiuser.h> 41#include <cutils/sched_policy.h> 42#include <utils/String8.h> 43#include <selinux/android.h> 44#include <processgroup/processgroup.h> 45 46#include "android_runtime/AndroidRuntime.h" 47#include "JNIHelp.h" 48#include "ScopedLocalRef.h" 49#include "ScopedPrimitiveArray.h" 50#include "ScopedUtfChars.h" 51 52namespace { 53 54using android::String8; 55 56static pid_t gSystemServerPid = 0; 57 58static const char kZygoteClassName[] = "com/android/internal/os/Zygote"; 59static jclass gZygoteClass; 60static jmethodID gCallPostForkChildHooks; 61 62// Must match values in com.android.internal.os.Zygote. 63enum MountExternalKind { 64 MOUNT_EXTERNAL_NONE = 0, 65 MOUNT_EXTERNAL_SINGLEUSER = 1, 66 MOUNT_EXTERNAL_MULTIUSER = 2, 67 MOUNT_EXTERNAL_MULTIUSER_ALL = 3, 68}; 69 70static void RuntimeAbort(JNIEnv* env) { 71 env->FatalError("RuntimeAbort"); 72} 73 74// This signal handler is for zygote mode, since the zygote must reap its children 75static void SigChldHandler(int /*signal_number*/) { 76 pid_t pid; 77 int status; 78 79 while ((pid = waitpid(-1, &status, WNOHANG)) > 0) { 80 // Log process-death status that we care about. In general it is 81 // not safe to call LOG(...) from a signal handler because of 82 // possible reentrancy. However, we know a priori that the 83 // current implementation of LOG() is safe to call from a SIGCHLD 84 // handler in the zygote process. If the LOG() implementation 85 // changes its locking strategy or its use of syscalls within the 86 // lazy-init critical section, its use here may become unsafe. 87 if (WIFEXITED(status)) { 88 if (WEXITSTATUS(status)) { 89 ALOGI("Process %d exited cleanly (%d)", pid, WEXITSTATUS(status)); 90 } 91 } else if (WIFSIGNALED(status)) { 92 if (WTERMSIG(status) != SIGKILL) { 93 ALOGI("Process %d exited due to signal (%d)", pid, WTERMSIG(status)); 94 } 95 if (WCOREDUMP(status)) { 96 ALOGI("Process %d dumped core.", pid); 97 } 98 } 99 100 // If the just-crashed process is the system_server, bring down zygote 101 // so that it is restarted by init and system server will be restarted 102 // from there. 103 if (pid == gSystemServerPid) { 104 ALOGE("Exit zygote because system server (%d) has terminated"); 105 kill(getpid(), SIGKILL); 106 } 107 } 108 109 // Note that we shouldn't consider ECHILD an error because 110 // the secondary zygote might have no children left to wait for. 111 if (pid < 0 && errno != ECHILD) { 112 ALOGW("Zygote SIGCHLD error in waitpid: %s", strerror(errno)); 113 } 114} 115 116// Configures the SIGCHLD handler for the zygote process. This is configured 117// very late, because earlier in the runtime we may fork() and exec() 118// other processes, and we want to waitpid() for those rather than 119// have them be harvested immediately. 120// 121// This ends up being called repeatedly before each fork(), but there's 122// no real harm in that. 123static void SetSigChldHandler() { 124 struct sigaction sa; 125 memset(&sa, 0, sizeof(sa)); 126 sa.sa_handler = SigChldHandler; 127 128 int err = sigaction(SIGCHLD, &sa, NULL); 129 if (err < 0) { 130 ALOGW("Error setting SIGCHLD handler: %d", errno); 131 } 132} 133 134// Sets the SIGCHLD handler back to default behavior in zygote children. 135static void UnsetSigChldHandler() { 136 struct sigaction sa; 137 memset(&sa, 0, sizeof(sa)); 138 sa.sa_handler = SIG_DFL; 139 140 int err = sigaction(SIGCHLD, &sa, NULL); 141 if (err < 0) { 142 ALOGW("Error unsetting SIGCHLD handler: %d", errno); 143 } 144} 145 146// Calls POSIX setgroups() using the int[] object as an argument. 147// A NULL argument is tolerated. 148static void SetGids(JNIEnv* env, jintArray javaGids) { 149 if (javaGids == NULL) { 150 return; 151 } 152 153 ScopedIntArrayRO gids(env, javaGids); 154 if (gids.get() == NULL) { 155 RuntimeAbort(env); 156 } 157 int rc = setgroups(gids.size(), reinterpret_cast<const gid_t*>(&gids[0])); 158 if (rc == -1) { 159 ALOGE("setgroups failed"); 160 RuntimeAbort(env); 161 } 162} 163 164// Sets the resource limits via setrlimit(2) for the values in the 165// two-dimensional array of integers that's passed in. The second dimension 166// contains a tuple of length 3: (resource, rlim_cur, rlim_max). NULL is 167// treated as an empty array. 168static void SetRLimits(JNIEnv* env, jobjectArray javaRlimits) { 169 if (javaRlimits == NULL) { 170 return; 171 } 172 173 rlimit rlim; 174 memset(&rlim, 0, sizeof(rlim)); 175 176 for (int i = 0; i < env->GetArrayLength(javaRlimits); ++i) { 177 ScopedLocalRef<jobject> javaRlimitObject(env, env->GetObjectArrayElement(javaRlimits, i)); 178 ScopedIntArrayRO javaRlimit(env, reinterpret_cast<jintArray>(javaRlimitObject.get())); 179 if (javaRlimit.size() != 3) { 180 ALOGE("rlimits array must have a second dimension of size 3"); 181 RuntimeAbort(env); 182 } 183 184 rlim.rlim_cur = javaRlimit[1]; 185 rlim.rlim_max = javaRlimit[2]; 186 187 int rc = setrlimit(javaRlimit[0], &rlim); 188 if (rc == -1) { 189 ALOGE("setrlimit(%d, {%d, %d}) failed", javaRlimit[0], rlim.rlim_cur, rlim.rlim_max); 190 RuntimeAbort(env); 191 } 192 } 193} 194 195// The debug malloc library needs to know whether it's the zygote or a child. 196extern "C" int gMallocLeakZygoteChild; 197 198static void EnableKeepCapabilities(JNIEnv* env) { 199 int rc = prctl(PR_SET_KEEPCAPS, 1, 0, 0, 0); 200 if (rc == -1) { 201 ALOGE("prctl(PR_SET_KEEPCAPS) failed"); 202 RuntimeAbort(env); 203 } 204} 205 206static void DropCapabilitiesBoundingSet(JNIEnv* env) { 207 for (int i = 0; prctl(PR_CAPBSET_READ, i, 0, 0, 0) >= 0; i++) { 208 int rc = prctl(PR_CAPBSET_DROP, i, 0, 0, 0); 209 if (rc == -1) { 210 if (errno == EINVAL) { 211 ALOGE("prctl(PR_CAPBSET_DROP) failed with EINVAL. Please verify " 212 "your kernel is compiled with file capabilities support"); 213 } else { 214 ALOGE("prctl(PR_CAPBSET_DROP) failed"); 215 RuntimeAbort(env); 216 } 217 } 218 } 219} 220 221static void SetCapabilities(JNIEnv* env, int64_t permitted, int64_t effective) { 222 __user_cap_header_struct capheader; 223 memset(&capheader, 0, sizeof(capheader)); 224 capheader.version = _LINUX_CAPABILITY_VERSION_3; 225 capheader.pid = 0; 226 227 __user_cap_data_struct capdata[2]; 228 memset(&capdata, 0, sizeof(capdata)); 229 capdata[0].effective = effective; 230 capdata[1].effective = effective >> 32; 231 capdata[0].permitted = permitted; 232 capdata[1].permitted = permitted >> 32; 233 234 if (capset(&capheader, &capdata[0]) == -1) { 235 ALOGE("capset(%lld, %lld) failed", permitted, effective); 236 RuntimeAbort(env); 237 } 238} 239 240static void SetSchedulerPolicy(JNIEnv* env) { 241 errno = -set_sched_policy(0, SP_DEFAULT); 242 if (errno != 0) { 243 ALOGE("set_sched_policy(0, SP_DEFAULT) failed"); 244 RuntimeAbort(env); 245 } 246} 247 248// Create a private mount namespace and bind mount appropriate emulated 249// storage for the given user. 250static bool MountEmulatedStorage(uid_t uid, jint mount_mode) { 251 if (mount_mode == MOUNT_EXTERNAL_NONE) { 252 return true; 253 } 254 255 // See storage config details at http://source.android.com/tech/storage/ 256 userid_t user_id = multiuser_get_user_id(uid); 257 258 // Create a second private mount namespace for our process 259 if (unshare(CLONE_NEWNS) == -1) { 260 ALOGW("Failed to unshare(): %d", errno); 261 return false; 262 } 263 264 // Create bind mounts to expose external storage 265 if (mount_mode == MOUNT_EXTERNAL_MULTIUSER || mount_mode == MOUNT_EXTERNAL_MULTIUSER_ALL) { 266 // These paths must already be created by init.rc 267 const char* source = getenv("EMULATED_STORAGE_SOURCE"); 268 const char* target = getenv("EMULATED_STORAGE_TARGET"); 269 const char* legacy = getenv("EXTERNAL_STORAGE"); 270 if (source == NULL || target == NULL || legacy == NULL) { 271 ALOGW("Storage environment undefined; unable to provide external storage"); 272 return false; 273 } 274 275 // Prepare source paths 276 277 // /mnt/shell/emulated/0 278 const String8 source_user(String8::format("%s/%d", source, user_id)); 279 // /storage/emulated/0 280 const String8 target_user(String8::format("%s/%d", target, user_id)); 281 282 if (fs_prepare_dir(source_user.string(), 0000, 0, 0) == -1 283 || fs_prepare_dir(target_user.string(), 0000, 0, 0) == -1) { 284 return false; 285 } 286 287 if (mount_mode == MOUNT_EXTERNAL_MULTIUSER_ALL) { 288 // Mount entire external storage tree for all users 289 if (TEMP_FAILURE_RETRY(mount(source, target, NULL, MS_BIND, NULL)) == -1) { 290 ALOGW("Failed to mount %s to %s :%d", source, target, errno); 291 return false; 292 } 293 } else { 294 // Only mount user-specific external storage 295 if (TEMP_FAILURE_RETRY( 296 mount(source_user.string(), target_user.string(), NULL, MS_BIND, NULL)) == -1) { 297 ALOGW("Failed to mount %s to %s: %d", source_user.string(), target_user.string(), errno); 298 return false; 299 } 300 } 301 302 if (fs_prepare_dir(legacy, 0000, 0, 0) == -1) { 303 return false; 304 } 305 306 // Finally, mount user-specific path into place for legacy users 307 if (TEMP_FAILURE_RETRY( 308 mount(target_user.string(), legacy, NULL, MS_BIND | MS_REC, NULL)) == -1) { 309 ALOGW("Failed to mount %s to %s: %d", target_user.string(), legacy, errno); 310 return false; 311 } 312 } else { 313 ALOGW("Mount mode %d unsupported", mount_mode); 314 return false; 315 } 316 317 return true; 318} 319 320static bool NeedsNoRandomizeWorkaround() { 321#if !defined(__arm__) 322 return false; 323#else 324 int major; 325 int minor; 326 struct utsname uts; 327 if (uname(&uts) == -1) { 328 return false; 329 } 330 331 if (sscanf(uts.release, "%d.%d", &major, &minor) != 2) { 332 return false; 333 } 334 335 // Kernels before 3.4.* need the workaround. 336 return (major < 3) || ((major == 3) && (minor < 4)); 337#endif 338} 339 340// Utility to close down the Zygote socket file descriptors while 341// the child is still running as root with Zygote's privileges. Each 342// descriptor (if any) is closed via dup2(), replacing it with a valid 343// (open) descriptor to /dev/null. 344 345static void DetachDescriptors(JNIEnv* env, jintArray fdsToClose) { 346 if (!fdsToClose) { 347 return; 348 } 349 jsize count = env->GetArrayLength(fdsToClose); 350 jint *ar = env->GetIntArrayElements(fdsToClose, 0); 351 if (!ar) { 352 ALOGE("Bad fd array"); 353 RuntimeAbort(env); 354 } 355 jsize i; 356 int devnull; 357 for (i = 0; i < count; i++) { 358 devnull = open("/dev/null", O_RDWR); 359 if (devnull < 0) { 360 ALOGE("Failed to open /dev/null"); 361 RuntimeAbort(env); 362 continue; 363 } 364 ALOGV("Switching descriptor %d to /dev/null: %d", ar[i], errno); 365 if (dup2(devnull, ar[i]) < 0) { 366 ALOGE("Failed dup2() on descriptor %d", ar[i]); 367 RuntimeAbort(env); 368 } 369 close(devnull); 370 } 371} 372 373void SetThreadName(const char* thread_name) { 374 bool hasAt = false; 375 bool hasDot = false; 376 const char* s = thread_name; 377 while (*s) { 378 if (*s == '.') { 379 hasDot = true; 380 } else if (*s == '@') { 381 hasAt = true; 382 } 383 s++; 384 } 385 const int len = s - thread_name; 386 if (len < 15 || hasAt || !hasDot) { 387 s = thread_name; 388 } else { 389 s = thread_name + len - 15; 390 } 391 // pthread_setname_np fails rather than truncating long strings. 392 char buf[16]; // MAX_TASK_COMM_LEN=16 is hard-coded into bionic 393 strlcpy(buf, s, sizeof(buf)-1); 394 errno = pthread_setname_np(pthread_self(), buf); 395 if (errno != 0) { 396 ALOGW("Unable to set the name of current thread to '%s'", buf); 397 } 398} 399 400// Utility routine to fork zygote and specialize the child process. 401static pid_t ForkAndSpecializeCommon(JNIEnv* env, uid_t uid, gid_t gid, jintArray javaGids, 402 jint debug_flags, jobjectArray javaRlimits, 403 jlong permittedCapabilities, jlong effectiveCapabilities, 404 jint mount_external, 405 jstring java_se_info, jstring java_se_name, 406 bool is_system_server, jintArray fdsToClose) { 407 SetSigChldHandler(); 408 409 pid_t pid = fork(); 410 411 if (pid == 0) { 412 // The child process. 413 gMallocLeakZygoteChild = 1; 414 415 // Clean up any descriptors which must be closed immediately 416 DetachDescriptors(env, fdsToClose); 417 418 // Keep capabilities across UID change, unless we're staying root. 419 if (uid != 0) { 420 EnableKeepCapabilities(env); 421 } 422 423 DropCapabilitiesBoundingSet(env); 424 425 if (!MountEmulatedStorage(uid, mount_external)) { 426 ALOGW("Failed to mount emulated storage: %d", errno); 427 if (errno == ENOTCONN || errno == EROFS) { 428 // When device is actively encrypting, we get ENOTCONN here 429 // since FUSE was mounted before the framework restarted. 430 // When encrypted device is booting, we get EROFS since 431 // FUSE hasn't been created yet by init. 432 // In either case, continue without external storage. 433 } else { 434 ALOGE("Cannot continue without emulated storage"); 435 RuntimeAbort(env); 436 } 437 } 438 439 if (!is_system_server) { 440 int rc = createProcessGroup(uid, getpid()); 441 if (rc != 0) { 442 ALOGE("createProcessGroup(%d, %d) failed: %s", uid, pid, strerror(-rc)); 443 RuntimeAbort(env); 444 } 445 } 446 447 SetGids(env, javaGids); 448 449 SetRLimits(env, javaRlimits); 450 451 int rc = setresgid(gid, gid, gid); 452 if (rc == -1) { 453 ALOGE("setresgid(%d) failed", gid); 454 RuntimeAbort(env); 455 } 456 457 rc = setresuid(uid, uid, uid); 458 if (rc == -1) { 459 ALOGE("setresuid(%d) failed", uid); 460 RuntimeAbort(env); 461 } 462 463 if (NeedsNoRandomizeWorkaround()) { 464 // Work around ARM kernel ASLR lossage (http://b/5817320). 465 int old_personality = personality(0xffffffff); 466 int new_personality = personality(old_personality | ADDR_NO_RANDOMIZE); 467 if (new_personality == -1) { 468 ALOGW("personality(%d) failed", new_personality); 469 } 470 } 471 472 SetCapabilities(env, permittedCapabilities, effectiveCapabilities); 473 474 SetSchedulerPolicy(env); 475 476 const char* se_info_c_str = NULL; 477 ScopedUtfChars* se_info = NULL; 478 if (java_se_info != NULL) { 479 se_info = new ScopedUtfChars(env, java_se_info); 480 se_info_c_str = se_info->c_str(); 481 if (se_info_c_str == NULL) { 482 ALOGE("se_info_c_str == NULL"); 483 RuntimeAbort(env); 484 } 485 } 486 const char* se_name_c_str = NULL; 487 ScopedUtfChars* se_name = NULL; 488 if (java_se_name != NULL) { 489 se_name = new ScopedUtfChars(env, java_se_name); 490 se_name_c_str = se_name->c_str(); 491 if (se_name_c_str == NULL) { 492 ALOGE("se_name_c_str == NULL"); 493 RuntimeAbort(env); 494 } 495 } 496 rc = selinux_android_setcontext(uid, is_system_server, se_info_c_str, se_name_c_str); 497 if (rc == -1) { 498 ALOGE("selinux_android_setcontext(%d, %d, \"%s\", \"%s\") failed", uid, 499 is_system_server, se_info_c_str, se_name_c_str); 500 RuntimeAbort(env); 501 } 502 503 // Make it easier to debug audit logs by setting the main thread's name to the 504 // nice name rather than "app_process". 505 if (se_info_c_str == NULL && is_system_server) { 506 se_name_c_str = "system_server"; 507 } 508 if (se_info_c_str != NULL) { 509 SetThreadName(se_name_c_str); 510 } 511 512 delete se_info; 513 delete se_name; 514 515 UnsetSigChldHandler(); 516 517 env->CallStaticVoidMethod(gZygoteClass, gCallPostForkChildHooks, debug_flags); 518 if (env->ExceptionCheck()) { 519 ALOGE("Error calling post fork hooks."); 520 RuntimeAbort(env); 521 } 522 } else if (pid > 0) { 523 // the parent process 524 } 525 return pid; 526} 527} // anonymous namespace 528 529namespace android { 530 531static jint com_android_internal_os_Zygote_nativeForkAndSpecialize( 532 JNIEnv* env, jclass, jint uid, jint gid, jintArray gids, 533 jint debug_flags, jobjectArray rlimits, 534 jint mount_external, jstring se_info, jstring se_name, 535 jintArray fdsToClose) { 536 return ForkAndSpecializeCommon(env, uid, gid, gids, debug_flags, 537 rlimits, 0, 0, mount_external, se_info, se_name, false, fdsToClose); 538} 539 540static jint com_android_internal_os_Zygote_nativeForkSystemServer( 541 JNIEnv* env, jclass, uid_t uid, gid_t gid, jintArray gids, 542 jint debug_flags, jobjectArray rlimits, jlong permittedCapabilities, 543 jlong effectiveCapabilities) { 544 pid_t pid = ForkAndSpecializeCommon(env, uid, gid, gids, 545 debug_flags, rlimits, 546 permittedCapabilities, effectiveCapabilities, 547 MOUNT_EXTERNAL_NONE, NULL, NULL, true, NULL); 548 if (pid > 0) { 549 // The zygote process checks whether the child process has died or not. 550 ALOGI("System server process %d has been created", pid); 551 gSystemServerPid = pid; 552 // There is a slight window that the system server process has crashed 553 // but it went unnoticed because we haven't published its pid yet. So 554 // we recheck here just to make sure that all is well. 555 int status; 556 if (waitpid(pid, &status, WNOHANG) == pid) { 557 ALOGE("System server process %d has died. Restarting Zygote!", pid); 558 RuntimeAbort(env); 559 } 560 } 561 return pid; 562} 563 564static JNINativeMethod gMethods[] = { 565 { "nativeForkAndSpecialize", "(II[II[[IILjava/lang/String;Ljava/lang/String;[I)I", 566 (void *) com_android_internal_os_Zygote_nativeForkAndSpecialize }, 567 { "nativeForkSystemServer", "(II[II[[IJJ)I", 568 (void *) com_android_internal_os_Zygote_nativeForkSystemServer } 569}; 570 571int register_com_android_internal_os_Zygote(JNIEnv* env) { 572 gZygoteClass = (jclass) env->NewGlobalRef(env->FindClass(kZygoteClassName)); 573 if (gZygoteClass == NULL) { 574 RuntimeAbort(env); 575 } 576 gCallPostForkChildHooks = env->GetStaticMethodID(gZygoteClass, "callPostForkChildHooks", "(I)V"); 577 578 return AndroidRuntime::registerNativeMethods(env, "com/android/internal/os/Zygote", 579 gMethods, NELEM(gMethods)); 580} 581} // namespace android 582 583