com_android_internal_os_Zygote.cpp revision 18cd9f57621b47889bdf81b2b04413569a999ef4
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 45#include "android_runtime/AndroidRuntime.h" 46#include "JNIHelp.h" 47#include "ScopedLocalRef.h" 48#include "ScopedPrimitiveArray.h" 49#include "ScopedUtfChars.h" 50 51namespace { 52 53using android::String8; 54 55static pid_t gSystemServerPid = 0; 56 57static const char kZygoteClassName[] = "com/android/internal/os/Zygote"; 58static jclass gZygoteClass; 59static jmethodID gCallPostForkChildHooks; 60 61// Must match values in com.android.internal.os.Zygote. 62enum MountExternalKind { 63 MOUNT_EXTERNAL_NONE = 0, 64 MOUNT_EXTERNAL_SINGLEUSER = 1, 65 MOUNT_EXTERNAL_MULTIUSER = 2, 66 MOUNT_EXTERNAL_MULTIUSER_ALL = 3, 67}; 68 69static void RuntimeAbort(JNIEnv* env) { 70 env->FatalError("RuntimeAbort"); 71} 72 73// This signal handler is for zygote mode, since the zygote must reap its children 74static void SigChldHandler(int /*signal_number*/) { 75 pid_t pid; 76 int status; 77 78 while ((pid = waitpid(-1, &status, WNOHANG)) > 0) { 79 // Log process-death status that we care about. In general it is 80 // not safe to call LOG(...) from a signal handler because of 81 // possible reentrancy. However, we know a priori that the 82 // current implementation of LOG() is safe to call from a SIGCHLD 83 // handler in the zygote process. If the LOG() implementation 84 // changes its locking strategy or its use of syscalls within the 85 // lazy-init critical section, its use here may become unsafe. 86 if (WIFEXITED(status)) { 87 if (WEXITSTATUS(status)) { 88 ALOGI("Process %d exited cleanly (%d)", pid, WEXITSTATUS(status)); 89 } 90 } else if (WIFSIGNALED(status)) { 91 if (WTERMSIG(status) != SIGKILL) { 92 ALOGI("Process %d exited due to signal (%d)", pid, WTERMSIG(status)); 93 } 94 if (WCOREDUMP(status)) { 95 ALOGI("Process %d dumped core.", pid); 96 } 97 } 98 99 // If the just-crashed process is the system_server, bring down zygote 100 // so that it is restarted by init and system server will be restarted 101 // from there. 102 if (pid == gSystemServerPid) { 103 ALOGE("Exit zygote because system server (%d) has terminated"); 104 kill(getpid(), SIGKILL); 105 } 106 } 107 108 // Note that we shouldn't consider ECHILD an error because 109 // the secondary zygote might have no children left to wait for. 110 if (pid < 0 && errno != ECHILD) { 111 ALOGW("Zygote SIGCHLD error in waitpid: %s", strerror(errno)); 112 } 113} 114 115// Configures the SIGCHLD handler for the zygote process. This is configured 116// very late, because earlier in the runtime we may fork() and exec() 117// other processes, and we want to waitpid() for those rather than 118// have them be harvested immediately. 119// 120// This ends up being called repeatedly before each fork(), but there's 121// no real harm in that. 122static void SetSigChldHandler() { 123 struct sigaction sa; 124 memset(&sa, 0, sizeof(sa)); 125 sa.sa_handler = SigChldHandler; 126 127 int err = sigaction(SIGCHLD, &sa, NULL); 128 if (err < 0) { 129 ALOGW("Error setting SIGCHLD handler: %d", errno); 130 } 131} 132 133// Sets the SIGCHLD handler back to default behavior in zygote children. 134static void UnsetSigChldHandler() { 135 struct sigaction sa; 136 memset(&sa, 0, sizeof(sa)); 137 sa.sa_handler = SIG_DFL; 138 139 int err = sigaction(SIGCHLD, &sa, NULL); 140 if (err < 0) { 141 ALOGW("Error unsetting SIGCHLD handler: %d", errno); 142 } 143} 144 145// Calls POSIX setgroups() using the int[] object as an argument. 146// A NULL argument is tolerated. 147static void SetGids(JNIEnv* env, jintArray javaGids) { 148 if (javaGids == NULL) { 149 return; 150 } 151 152 ScopedIntArrayRO gids(env, javaGids); 153 if (gids.get() == NULL) { 154 RuntimeAbort(env); 155 } 156 int rc = setgroups(gids.size(), reinterpret_cast<const gid_t*>(&gids[0])); 157 if (rc == -1) { 158 ALOGE("setgroups failed"); 159 RuntimeAbort(env); 160 } 161} 162 163// Sets the resource limits via setrlimit(2) for the values in the 164// two-dimensional array of integers that's passed in. The second dimension 165// contains a tuple of length 3: (resource, rlim_cur, rlim_max). NULL is 166// treated as an empty array. 167static void SetRLimits(JNIEnv* env, jobjectArray javaRlimits) { 168 if (javaRlimits == NULL) { 169 return; 170 } 171 172 rlimit rlim; 173 memset(&rlim, 0, sizeof(rlim)); 174 175 for (int i = 0; i < env->GetArrayLength(javaRlimits); ++i) { 176 ScopedLocalRef<jobject> javaRlimitObject(env, env->GetObjectArrayElement(javaRlimits, i)); 177 ScopedIntArrayRO javaRlimit(env, reinterpret_cast<jintArray>(javaRlimitObject.get())); 178 if (javaRlimit.size() != 3) { 179 ALOGE("rlimits array must have a second dimension of size 3"); 180 RuntimeAbort(env); 181 } 182 183 rlim.rlim_cur = javaRlimit[1]; 184 rlim.rlim_max = javaRlimit[2]; 185 186 int rc = setrlimit(javaRlimit[0], &rlim); 187 if (rc == -1) { 188 ALOGE("setrlimit(%d, {%d, %d}) failed", javaRlimit[0], rlim.rlim_cur, rlim.rlim_max); 189 RuntimeAbort(env); 190 } 191 } 192} 193 194// The debug malloc library needs to know whether it's the zygote or a child. 195extern "C" int gMallocLeakZygoteChild; 196 197static void EnableKeepCapabilities(JNIEnv* env) { 198 int rc = prctl(PR_SET_KEEPCAPS, 1, 0, 0, 0); 199 if (rc == -1) { 200 ALOGE("prctl(PR_SET_KEEPCAPS) failed"); 201 RuntimeAbort(env); 202 } 203} 204 205static void DropCapabilitiesBoundingSet(JNIEnv* env) { 206 for (int i = 0; prctl(PR_CAPBSET_READ, i, 0, 0, 0) >= 0; i++) { 207 int rc = prctl(PR_CAPBSET_DROP, i, 0, 0, 0); 208 if (rc == -1) { 209 if (errno == EINVAL) { 210 ALOGE("prctl(PR_CAPBSET_DROP) failed with EINVAL. Please verify " 211 "your kernel is compiled with file capabilities support"); 212 } else { 213 ALOGE("prctl(PR_CAPBSET_DROP) failed"); 214 RuntimeAbort(env); 215 } 216 } 217 } 218} 219 220static void SetCapabilities(JNIEnv* env, int64_t permitted, int64_t effective) { 221 __user_cap_header_struct capheader; 222 memset(&capheader, 0, sizeof(capheader)); 223 capheader.version = _LINUX_CAPABILITY_VERSION_3; 224 capheader.pid = 0; 225 226 __user_cap_data_struct capdata[2]; 227 memset(&capdata, 0, sizeof(capdata)); 228 capdata[0].effective = effective; 229 capdata[1].effective = effective >> 32; 230 capdata[0].permitted = permitted; 231 capdata[1].permitted = permitted >> 32; 232 233 if (capset(&capheader, &capdata[0]) == -1) { 234 ALOGE("capset(%lld, %lld) failed", permitted, effective); 235 RuntimeAbort(env); 236 } 237} 238 239static void SetSchedulerPolicy(JNIEnv* env) { 240 errno = -set_sched_policy(0, SP_DEFAULT); 241 if (errno != 0) { 242 ALOGE("set_sched_policy(0, SP_DEFAULT) failed"); 243 RuntimeAbort(env); 244 } 245} 246 247// Create a private mount namespace and bind mount appropriate emulated 248// storage for the given user. 249static bool MountEmulatedStorage(uid_t uid, jint mount_mode) { 250 if (mount_mode == MOUNT_EXTERNAL_NONE) { 251 return true; 252 } 253 254 // See storage config details at http://source.android.com/tech/storage/ 255 userid_t user_id = multiuser_get_user_id(uid); 256 257 // Create a second private mount namespace for our process 258 if (unshare(CLONE_NEWNS) == -1) { 259 ALOGW("Failed to unshare(): %d", errno); 260 return false; 261 } 262 263 // Create bind mounts to expose external storage 264 if (mount_mode == MOUNT_EXTERNAL_MULTIUSER || mount_mode == MOUNT_EXTERNAL_MULTIUSER_ALL) { 265 // These paths must already be created by init.rc 266 const char* source = getenv("EMULATED_STORAGE_SOURCE"); 267 const char* target = getenv("EMULATED_STORAGE_TARGET"); 268 const char* legacy = getenv("EXTERNAL_STORAGE"); 269 if (source == NULL || target == NULL || legacy == NULL) { 270 ALOGW("Storage environment undefined; unable to provide external storage"); 271 return false; 272 } 273 274 // Prepare source paths 275 276 // /mnt/shell/emulated/0 277 const String8 source_user(String8::format("%s/%d", source, user_id)); 278 // /storage/emulated/0 279 const String8 target_user(String8::format("%s/%d", target, user_id)); 280 281 if (fs_prepare_dir(source_user.string(), 0000, 0, 0) == -1 282 || fs_prepare_dir(target_user.string(), 0000, 0, 0) == -1) { 283 return false; 284 } 285 286 if (mount_mode == MOUNT_EXTERNAL_MULTIUSER_ALL) { 287 // Mount entire external storage tree for all users 288 if (TEMP_FAILURE_RETRY(mount(source, target, NULL, MS_BIND, NULL)) == -1) { 289 ALOGW("Failed to mount %s to %s :%d", source, target, errno); 290 return false; 291 } 292 } else { 293 // Only mount user-specific external storage 294 if (TEMP_FAILURE_RETRY( 295 mount(source_user.string(), target_user.string(), NULL, MS_BIND, NULL)) == -1) { 296 ALOGW("Failed to mount %s to %s: %d", source_user.string(), target_user.string(), errno); 297 return false; 298 } 299 } 300 301 if (fs_prepare_dir(legacy, 0000, 0, 0) == -1) { 302 return false; 303 } 304 305 // Finally, mount user-specific path into place for legacy users 306 if (TEMP_FAILURE_RETRY( 307 mount(target_user.string(), legacy, NULL, MS_BIND | MS_REC, NULL)) == -1) { 308 ALOGW("Failed to mount %s to %s: %d", target_user.string(), legacy, errno); 309 return false; 310 } 311 } else { 312 ALOGW("Mount mode %d unsupported", mount_mode); 313 return false; 314 } 315 316 return true; 317} 318 319static bool NeedsNoRandomizeWorkaround() { 320#if !defined(__arm__) 321 return false; 322#else 323 int major; 324 int minor; 325 struct utsname uts; 326 if (uname(&uts) == -1) { 327 return false; 328 } 329 330 if (sscanf(uts.release, "%d.%d", &major, &minor) != 2) { 331 return false; 332 } 333 334 // Kernels before 3.4.* need the workaround. 335 return (major < 3) || ((major == 3) && (minor < 4)); 336#endif 337} 338 339// Utility to close down the Zygote socket file descriptors while 340// the child is still running as root with Zygote's privileges. Each 341// descriptor (if any) is closed via dup2(), replacing it with a valid 342// (open) descriptor to /dev/null. 343 344static void DetachDescriptors(JNIEnv* env, jintArray fdsToClose) { 345 if (!fdsToClose) { 346 return; 347 } 348 jsize count = env->GetArrayLength(fdsToClose); 349 jint *ar = env->GetIntArrayElements(fdsToClose, 0); 350 if (!ar) { 351 ALOGE("Bad fd array"); 352 RuntimeAbort(env); 353 } 354 jsize i; 355 int devnull; 356 for (i = 0; i < count; i++) { 357 devnull = open("/dev/null", O_RDWR); 358 if (devnull < 0) { 359 ALOGE("Failed to open /dev/null"); 360 RuntimeAbort(env); 361 continue; 362 } 363 ALOGV("Switching descriptor %d to /dev/null: %d", ar[i], errno); 364 if (dup2(devnull, ar[i]) < 0) { 365 ALOGE("Failed dup2() on descriptor %d", ar[i]); 366 RuntimeAbort(env); 367 } 368 close(devnull); 369 } 370} 371 372void SetThreadName(const char* thread_name) { 373 bool hasAt = false; 374 bool hasDot = false; 375 const char* s = thread_name; 376 while (*s) { 377 if (*s == '.') { 378 hasDot = true; 379 } else if (*s == '@') { 380 hasAt = true; 381 } 382 s++; 383 } 384 const int len = s - thread_name; 385 if (len < 15 || hasAt || !hasDot) { 386 s = thread_name; 387 } else { 388 s = thread_name + len - 15; 389 } 390 // pthread_setname_np fails rather than truncating long strings. 391 char buf[16]; // MAX_TASK_COMM_LEN=16 is hard-coded into bionic 392 strlcpy(buf, s, sizeof(buf)-1); 393 errno = pthread_setname_np(pthread_self(), buf); 394 if (errno != 0) { 395 ALOGW("Unable to set the name of current thread to '%s'", buf); 396 } 397} 398 399// Utility routine to fork zygote and specialize the child process. 400static pid_t ForkAndSpecializeCommon(JNIEnv* env, uid_t uid, gid_t gid, jintArray javaGids, 401 jint debug_flags, jobjectArray javaRlimits, 402 jlong permittedCapabilities, jlong effectiveCapabilities, 403 jint mount_external, 404 jstring java_se_info, jstring java_se_name, 405 bool is_system_server, jintArray fdsToClose) { 406 SetSigChldHandler(); 407 408 pid_t pid = fork(); 409 410 if (pid == 0) { 411 // The child process. 412 gMallocLeakZygoteChild = 1; 413 414 // Clean up any descriptors which must be closed immediately 415 DetachDescriptors(env, fdsToClose); 416 417 // Keep capabilities across UID change, unless we're staying root. 418 if (uid != 0) { 419 EnableKeepCapabilities(env); 420 } 421 422 DropCapabilitiesBoundingSet(env); 423 424 if (!MountEmulatedStorage(uid, mount_external)) { 425 ALOGW("Failed to mount emulated storage: %d", errno); 426 if (errno == ENOTCONN || errno == EROFS) { 427 // When device is actively encrypting, we get ENOTCONN here 428 // since FUSE was mounted before the framework restarted. 429 // When encrypted device is booting, we get EROFS since 430 // FUSE hasn't been created yet by init. 431 // In either case, continue without external storage. 432 } else { 433 ALOGE("Cannot continue without emulated storage"); 434 RuntimeAbort(env); 435 } 436 } 437 438 SetGids(env, javaGids); 439 440 SetRLimits(env, javaRlimits); 441 442 int rc = setresgid(gid, gid, gid); 443 if (rc == -1) { 444 ALOGE("setresgid(%d) failed", gid); 445 RuntimeAbort(env); 446 } 447 448 rc = setresuid(uid, uid, uid); 449 if (rc == -1) { 450 ALOGE("setresuid(%d) failed", uid); 451 RuntimeAbort(env); 452 } 453 454 if (NeedsNoRandomizeWorkaround()) { 455 // Work around ARM kernel ASLR lossage (http://b/5817320). 456 int old_personality = personality(0xffffffff); 457 int new_personality = personality(old_personality | ADDR_NO_RANDOMIZE); 458 if (new_personality == -1) { 459 ALOGW("personality(%d) failed", new_personality); 460 } 461 } 462 463 SetCapabilities(env, permittedCapabilities, effectiveCapabilities); 464 465 SetSchedulerPolicy(env); 466 467 const char* se_info_c_str = NULL; 468 ScopedUtfChars* se_info = NULL; 469 if (java_se_info != NULL) { 470 se_info = new ScopedUtfChars(env, java_se_info); 471 se_info_c_str = se_info->c_str(); 472 if (se_info_c_str == NULL) { 473 ALOGE("se_info_c_str == NULL"); 474 RuntimeAbort(env); 475 } 476 } 477 const char* se_name_c_str = NULL; 478 ScopedUtfChars* se_name = NULL; 479 if (java_se_name != NULL) { 480 se_name = new ScopedUtfChars(env, java_se_name); 481 se_name_c_str = se_name->c_str(); 482 if (se_name_c_str == NULL) { 483 ALOGE("se_name_c_str == NULL"); 484 RuntimeAbort(env); 485 } 486 } 487 rc = selinux_android_setcontext(uid, is_system_server, se_info_c_str, se_name_c_str); 488 if (rc == -1) { 489 ALOGE("selinux_android_setcontext(%d, %d, \"%s\", \"%s\") failed", uid, 490 is_system_server, se_info_c_str, se_name_c_str); 491 RuntimeAbort(env); 492 } 493 494 // Make it easier to debug audit logs by setting the main thread's name to the 495 // nice name rather than "app_process". 496 if (se_info_c_str == NULL && is_system_server) { 497 se_name_c_str = "system_server"; 498 } 499 if (se_info_c_str != NULL) { 500 SetThreadName(se_name_c_str); 501 } 502 503 delete se_info; 504 delete se_name; 505 506 UnsetSigChldHandler(); 507 508 env->CallStaticVoidMethod(gZygoteClass, gCallPostForkChildHooks, debug_flags); 509 if (env->ExceptionCheck()) { 510 ALOGE("Error calling post fork hooks."); 511 RuntimeAbort(env); 512 } 513 } else if (pid > 0) { 514 // the parent process 515 } 516 return pid; 517} 518} // anonymous namespace 519 520namespace android { 521 522static jint com_android_internal_os_Zygote_nativeForkAndSpecialize( 523 JNIEnv* env, jclass, jint uid, jint gid, jintArray gids, 524 jint debug_flags, jobjectArray rlimits, 525 jint mount_external, jstring se_info, jstring se_name, 526 jintArray fdsToClose) { 527 return ForkAndSpecializeCommon(env, uid, gid, gids, debug_flags, 528 rlimits, 0, 0, mount_external, se_info, se_name, false, fdsToClose); 529} 530 531static jint com_android_internal_os_Zygote_nativeForkSystemServer( 532 JNIEnv* env, jclass, uid_t uid, gid_t gid, jintArray gids, 533 jint debug_flags, jobjectArray rlimits, jlong permittedCapabilities, 534 jlong effectiveCapabilities) { 535 pid_t pid = ForkAndSpecializeCommon(env, uid, gid, gids, 536 debug_flags, rlimits, 537 permittedCapabilities, effectiveCapabilities, 538 MOUNT_EXTERNAL_NONE, NULL, NULL, true, NULL); 539 if (pid > 0) { 540 // The zygote process checks whether the child process has died or not. 541 ALOGI("System server process %d has been created", pid); 542 gSystemServerPid = pid; 543 // There is a slight window that the system server process has crashed 544 // but it went unnoticed because we haven't published its pid yet. So 545 // we recheck here just to make sure that all is well. 546 int status; 547 if (waitpid(pid, &status, WNOHANG) == pid) { 548 ALOGE("System server process %d has died. Restarting Zygote!", pid); 549 RuntimeAbort(env); 550 } 551 } 552 return pid; 553} 554 555static JNINativeMethod gMethods[] = { 556 { "nativeForkAndSpecialize", "(II[II[[IILjava/lang/String;Ljava/lang/String;[I)I", 557 (void *) com_android_internal_os_Zygote_nativeForkAndSpecialize }, 558 { "nativeForkSystemServer", "(II[II[[IJJ)I", 559 (void *) com_android_internal_os_Zygote_nativeForkSystemServer } 560}; 561 562int register_com_android_internal_os_Zygote(JNIEnv* env) { 563 gZygoteClass = (jclass) env->NewGlobalRef(env->FindClass(kZygoteClassName)); 564 if (gZygoteClass == NULL) { 565 RuntimeAbort(env); 566 } 567 gCallPostForkChildHooks = env->GetStaticMethodID(gZygoteClass, "callPostForkChildHooks", "(I)V"); 568 569 return AndroidRuntime::registerNativeMethods(env, "com/android/internal/os/Zygote", 570 gMethods, NELEM(gMethods)); 571} 572} // namespace android 573 574