summaryrefslogtreecommitdiffstats
blob: bd202ff14d08a5eb4e265934d32e1138599e549b (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
/*
 * Copyright (C) 2008 The Android Open Source Project
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *  * Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *  * Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include "debuggerd/handler.h"

#include <errno.h>
#include <fcntl.h>
#include <inttypes.h>
#include <linux/futex.h>
#include <pthread.h>
#include <sched.h>
#include <signal.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/capability.h>
#include <sys/mman.h>
#include <sys/prctl.h>
#include <sys/socket.h>
#include <sys/syscall.h>
#include <sys/un.h>
#include <sys/wait.h>
#include <unistd.h>

#include <android-base/unique_fd.h>
#include <async_safe/log.h>

#include "dump_type.h"

using android::base::unique_fd;

// see man(2) prctl, specifically the section about PR_GET_NAME
#define MAX_TASK_NAME_LEN (16)

#if defined(__LP64__)
#define CRASH_DUMP_NAME "crash_dump64"
#else
#define CRASH_DUMP_NAME "crash_dump32"
#endif

#define CRASH_DUMP_PATH "/system/bin/" CRASH_DUMP_NAME

// Wrappers that directly invoke the respective syscalls, in case the cached values are invalid.
#pragma GCC poison getpid gettid
static pid_t __getpid() {
  return syscall(__NR_getpid);
}

static pid_t __gettid() {
  return syscall(__NR_gettid);
}

static inline void futex_wait(volatile void* ftx, int value) {
  syscall(__NR_futex, ftx, FUTEX_WAIT, value, nullptr, nullptr, 0);
}

class ErrnoRestorer {
 public:
  ErrnoRestorer() : saved_errno_(errno) {
  }

  ~ErrnoRestorer() {
    errno = saved_errno_;
  }

 private:
  int saved_errno_;
};

extern "C" void debuggerd_fallback_handler(siginfo_t*, ucontext_t*, void*);

static debuggerd_callbacks_t g_callbacks;

// Mutex to ensure only one crashing thread dumps itself.
static pthread_mutex_t crash_mutex = PTHREAD_MUTEX_INITIALIZER;

// Don't use async_safe_fatal because it exits via abort, which might put us back into
// a signal handler.
static void __noreturn __printflike(1, 2) fatal(const char* fmt, ...) {
  va_list args;
  va_start(args, fmt);
  async_safe_format_log_va_list(ANDROID_LOG_FATAL, "libc", fmt, args);
  _exit(1);
}

static void __noreturn __printflike(1, 2) fatal_errno(const char* fmt, ...) {
  int err = errno;
  va_list args;
  va_start(args, fmt);

  char buf[4096];
  async_safe_format_buffer_va_list(buf, sizeof(buf), fmt, args);
  fatal("%s: %s", buf, strerror(err));
}

static bool get_main_thread_name(char* buf, size_t len) {
  unique_fd fd(open("/proc/self/comm", O_RDONLY | O_CLOEXEC));
  if (fd == -1) {
    return false;
  }

  ssize_t rc = read(fd, buf, len);
  if (rc == -1) {
    return false;
  } else if (rc == 0) {
    // Should never happen?
    return false;
  }

  // There's a trailing newline, replace it with a NUL.
  buf[rc - 1] = '\0';
  return true;
}

/*
 * Writes a summary of the signal to the log file.  We do this so that, if
 * for some reason we're not able to contact debuggerd, there is still some
 * indication of the failure in the log.
 *
 * We could be here as a result of native heap corruption, or while a
 * mutex is being held, so we don't want to use any libc functions that
 * could allocate memory or hold a lock.
 */
static void log_signal_summary(int signum, const siginfo_t* info) {
  char thread_name[MAX_TASK_NAME_LEN + 1];  // one more for termination
  if (prctl(PR_GET_NAME, reinterpret_cast<unsigned long>(thread_name), 0, 0, 0) != 0) {
    strcpy(thread_name, "<name unknown>");
  } else {
    // short names are null terminated by prctl, but the man page
    // implies that 16 byte names are not.
    thread_name[MAX_TASK_NAME_LEN] = 0;
  }

  if (signum == DEBUGGER_SIGNAL) {
    async_safe_format_log(ANDROID_LOG_INFO, "libc", "Requested dump for tid %d (%s)", __gettid(),
                          thread_name);
    return;
  }

  const char* signal_name = "???";
  bool has_address = false;
  switch (signum) {
    case SIGABRT:
      signal_name = "SIGABRT";
      break;
    case SIGBUS:
      signal_name = "SIGBUS";
      has_address = true;
      break;
    case SIGFPE:
      signal_name = "SIGFPE";
      has_address = true;
      break;
    case SIGILL:
      signal_name = "SIGILL";
      has_address = true;
      break;
    case SIGSEGV:
      signal_name = "SIGSEGV";
      has_address = true;
      break;
#if defined(SIGSTKFLT)
    case SIGSTKFLT:
      signal_name = "SIGSTKFLT";
      break;
#endif
    case SIGSYS:
      signal_name = "SIGSYS";
      break;
    case SIGTRAP:
      signal_name = "SIGTRAP";
      break;
  }

  // "info" will be null if the siginfo_t information was not available.
  // Many signals don't have an address or a code.
  char code_desc[32];  // ", code -6"
  char addr_desc[32];  // ", fault addr 0x1234"
  addr_desc[0] = code_desc[0] = 0;
  if (info != nullptr) {
    async_safe_format_buffer(code_desc, sizeof(code_desc), ", code %d", info->si_code);
    if (has_address) {
      async_safe_format_buffer(addr_desc, sizeof(addr_desc), ", fault addr %p", info->si_addr);
    }
  }

  char main_thread_name[MAX_TASK_NAME_LEN + 1];
  if (!get_main_thread_name(main_thread_name, sizeof(main_thread_name))) {
    strncpy(main_thread_name, "<unknown>", sizeof(main_thread_name));
  }

  async_safe_format_log(
      ANDROID_LOG_FATAL, "libc", "Fatal signal %d (%s)%s%s in tid %d (%s), pid %d (%s)", signum,
      signal_name, code_desc, addr_desc, __gettid(), thread_name, __getpid(), main_thread_name);
}

/*
 * Returns true if the handler for signal "signum" has SA_SIGINFO set.
 */
static bool have_siginfo(int signum) {
  struct sigaction old_action;
  if (sigaction(signum, nullptr, &old_action) < 0) {
    async_safe_format_log(ANDROID_LOG_WARN, "libc", "Failed testing for SA_SIGINFO: %s",
                          strerror(errno));
    return false;
  }
  return (old_action.sa_flags & SA_SIGINFO) != 0;
}

static void raise_caps() {
  // Raise CapInh to match CapPrm, so that we can set the ambient bits.
  __user_cap_header_struct capheader;
  memset(&capheader, 0, sizeof(capheader));
  capheader.version = _LINUX_CAPABILITY_VERSION_3;
  capheader.pid = 0;

  __user_cap_data_struct capdata[2];
  if (capget(&capheader, &capdata[0]) == -1) {
    fatal_errno("capget failed");
  }

  if (capdata[0].permitted != capdata[0].inheritable ||
      capdata[1].permitted != capdata[1].inheritable) {
    capdata[0].inheritable = capdata[0].permitted;
    capdata[1].inheritable = capdata[1].permitted;

    if (capset(&capheader, &capdata[0]) == -1) {
      async_safe_format_log(ANDROID_LOG_ERROR, "libc", "capset failed: %s", strerror(errno));
    }
  }

  // Set the ambient capability bits so that crash_dump gets all of our caps and can ptrace us.
  uint64_t capmask = capdata[0].inheritable;
  capmask |= static_cast<uint64_t>(capdata[1].inheritable) << 32;
  for (unsigned long i = 0; i < 64; ++i) {
    if (capmask & (1ULL << i)) {
      if (prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_RAISE, i, 0, 0) != 0) {
        async_safe_format_log(ANDROID_LOG_ERROR, "libc",
                              "failed to raise ambient capability %lu: %s", i, strerror(errno));
      }
    }
  }
}

struct debugger_thread_info {
  bool crash_dump_started;
  pid_t crashing_tid;
  pid_t pseudothread_tid;
  int signal_number;
  siginfo_t* info;
};

// Logging and contacting debuggerd requires free file descriptors, which we might not have.
// Work around this by spawning a "thread" that shares its parent's address space, but not its file
// descriptor table, so that we can close random file descriptors without affecting the original
// process. Note that this doesn't go through pthread_create, so TLS is shared with the spawning
// process.
static void* pseudothread_stack;

static DebuggerdDumpType get_dump_type(const debugger_thread_info* thread_info) {
  if (thread_info->signal_number == DEBUGGER_SIGNAL && thread_info->info->si_value.sival_int) {
    return kDebuggerdNativeBacktrace;
  }

  return kDebuggerdTombstone;
}

static int debuggerd_dispatch_pseudothread(void* arg) {
  debugger_thread_info* thread_info = static_cast<debugger_thread_info*>(arg);

  for (int i = 0; i < 1024; ++i) {
    close(i);
  }

  int devnull = TEMP_FAILURE_RETRY(open("/dev/null", O_RDWR));

  // devnull will be 0.
  TEMP_FAILURE_RETRY(dup2(devnull, STDOUT_FILENO));
  TEMP_FAILURE_RETRY(dup2(devnull, STDERR_FILENO));

  unique_fd pipe_read, pipe_write;
  if (!android::base::Pipe(&pipe_read, &pipe_write)) {
    fatal_errno("failed to create pipe");
  }

  // Don't use fork(2) to avoid calling pthread_atfork handlers.
  int forkpid = clone(nullptr, nullptr, 0, nullptr);
  if (forkpid == -1) {
    async_safe_format_log(ANDROID_LOG_FATAL, "libc",
                          "failed to fork in debuggerd signal handler: %s", strerror(errno));
  } else if (forkpid == 0) {
    TEMP_FAILURE_RETRY(dup2(pipe_write.get(), STDOUT_FILENO));
    pipe_write.reset();
    pipe_read.reset();

    raise_caps();

    char main_tid[10];
    char pseudothread_tid[10];
    char debuggerd_dump_type[10];
    async_safe_format_buffer(main_tid, sizeof(main_tid), "%d", thread_info->crashing_tid);
    async_safe_format_buffer(pseudothread_tid, sizeof(pseudothread_tid), "%d",
                             thread_info->pseudothread_tid);
    async_safe_format_buffer(debuggerd_dump_type, sizeof(debuggerd_dump_type), "%d",
                             get_dump_type(thread_info));

    execle(CRASH_DUMP_PATH, CRASH_DUMP_NAME, main_tid, pseudothread_tid, debuggerd_dump_type,
           nullptr, nullptr);

    fatal_errno("exec failed");
  } else {
    pipe_write.reset();
    char buf[4];
    ssize_t rc = TEMP_FAILURE_RETRY(read(pipe_read.get(), &buf, sizeof(buf)));
    if (rc == -1) {
      async_safe_format_log(ANDROID_LOG_FATAL, "libc", "read of IPC pipe failed: %s",
                            strerror(errno));
    } else if (rc == 0) {
      async_safe_format_log(ANDROID_LOG_FATAL, "libc", "crash_dump helper failed to exec");
    } else if (rc != 1) {
      async_safe_format_log(ANDROID_LOG_FATAL, "libc",
                            "read of IPC pipe returned unexpected value: %zd", rc);
    } else {
      if (buf[0] != '\1') {
        async_safe_format_log(ANDROID_LOG_FATAL, "libc", "crash_dump helper reported failure");
      } else {
        thread_info->crash_dump_started = true;
      }
    }
    pipe_read.reset();

    // Don't leave a zombie child.
    int status;
    if (TEMP_FAILURE_RETRY(waitpid(forkpid, &status, 0)) == -1) {
      async_safe_format_log(ANDROID_LOG_FATAL, "libc", "failed to wait for crash_dump helper: %s",
                            strerror(errno));
    } else if (WIFSTOPPED(status) || WIFSIGNALED(status)) {
      async_safe_format_log(ANDROID_LOG_FATAL, "libc", "crash_dump helper crashed or stopped");
      thread_info->crash_dump_started = false;
    }
  }

  syscall(__NR_exit, 0);
  return 0;
}

static void resend_signal(siginfo_t* info, bool crash_dump_started) {
  // Signals can either be fatal or nonfatal.
  // For fatal signals, crash_dump will send us the signal we crashed with
  // before resuming us, so that processes using waitpid on us will see that we
  // exited with the correct exit status (e.g. so that sh will report
  // "Segmentation fault" instead of "Killed"). For this to work, we need
  // to deregister our signal handler for that signal before continuing.
  if (info->si_signo != DEBUGGER_SIGNAL) {
    signal(info->si_signo, SIG_DFL);
  }

  // We need to return from our signal handler so that crash_dump can see the
  // signal via ptrace and dump the thread that crashed. However, returning
  // does not guarantee that the signal will be thrown again, even for SIGSEGV
  // and friends, since the signal could have been sent manually. We blocked
  // all signals when registering the handler, so resending the signal (using
  // rt_tgsigqueueinfo(2) to preserve SA_SIGINFO) will cause it to be delivered
  // when our signal handler returns.
  if (crash_dump_started || info->si_signo != DEBUGGER_SIGNAL) {
    int rc = syscall(SYS_rt_tgsigqueueinfo, __getpid(), __gettid(), info->si_signo, info);
    if (rc != 0) {
      fatal_errno("failed to resend signal during crash");
    }
  }
}

// Handler that does crash dumping by forking and doing the processing in the child.
// Do this by ptracing the relevant thread, and then execing debuggerd to do the actual dump.
static void debuggerd_signal_handler(int signal_number, siginfo_t* info, void* context) {
  // Make sure we don't change the value of errno, in case a signal comes in between the process
  // making a syscall and checking errno.
  ErrnoRestorer restorer;

  // It's possible somebody cleared the SA_SIGINFO flag, which would mean
  // our "info" arg holds an undefined value.
  if (!have_siginfo(signal_number)) {
    info = nullptr;
  }

  struct siginfo si = {};
  if (!info) {
    memset(&si, 0, sizeof(si));
    si.si_signo = signal_number;
    si.si_code = SI_USER;
    si.si_pid = __getpid();
    si.si_uid = getuid();
    info = &si;
  } else if (info->si_code >= 0 || info->si_code == SI_TKILL) {
    // rt_tgsigqueueinfo(2)'s documentation appears to be incorrect on kernels
    // that contain commit 66dd34a (3.9+). The manpage claims to only allow
    // negative si_code values that are not SI_TKILL, but 66dd34a changed the
    // check to allow all si_code values in calls coming from inside the house.
  }

  void* abort_message = nullptr;
  if (g_callbacks.get_abort_message) {
    abort_message = g_callbacks.get_abort_message();
  }

  // If sival_int is ~0, it means that the fallback handler has been called
  // once before and this function is being called again to dump the stack
  // of a specific thread. It is possible that the prctl call might return 1,
  // then return 0 in subsequent calls, so check the sival_int to determine if
  // the fallback handler should be called first.
  if (info->si_value.sival_int == ~0 || prctl(PR_GET_NO_NEW_PRIVS, 0, 0, 0, 0) == 1) {
    // This check might be racy if another thread sets NO_NEW_PRIVS, but this should be unlikely,
    // you can only set NO_NEW_PRIVS to 1, and the effect should be at worst a single missing
    // ANR trace.
    debuggerd_fallback_handler(info, static_cast<ucontext_t*>(context), abort_message);
    resend_signal(info, false);
    return;
  }

  // Only allow one thread to handle a signal at a time.
  int ret = pthread_mutex_lock(&crash_mutex);
  if (ret != 0) {
    async_safe_format_log(ANDROID_LOG_INFO, "libc", "pthread_mutex_lock failed: %s", strerror(ret));
    return;
  }

  log_signal_summary(signal_number, info);

  // If this was a fatal crash, populate si_value with the abort message address if possible.
  // Note that applications can set an abort message without aborting.
  if (abort_message && signal_number != DEBUGGER_SIGNAL) {
    info->si_value.sival_ptr = abort_message;
  }

  debugger_thread_info thread_info = {
    .crash_dump_started = false,
    .pseudothread_tid = -1,
    .crashing_tid = __gettid(),
    .signal_number = signal_number,
    .info = info
  };

  // Set PR_SET_DUMPABLE to 1, so that crash_dump can ptrace us.
  int orig_dumpable = prctl(PR_GET_DUMPABLE);
  if (prctl(PR_SET_DUMPABLE, 1) != 0) {
    fatal_errno("failed to set dumpable");
  }

  // Essentially pthread_create without CLONE_FILES (see debuggerd_dispatch_pseudothread).
  pid_t child_pid =
    clone(debuggerd_dispatch_pseudothread, pseudothread_stack,
          CLONE_THREAD | CLONE_SIGHAND | CLONE_VM | CLONE_CHILD_SETTID | CLONE_CHILD_CLEARTID,
          &thread_info, nullptr, nullptr, &thread_info.pseudothread_tid);
  if (child_pid == -1) {
    fatal_errno("failed to spawn debuggerd dispatch thread");
  }

  // Wait for the child to start...
  futex_wait(&thread_info.pseudothread_tid, -1);

  // and then wait for it to finish.
  futex_wait(&thread_info.pseudothread_tid, child_pid);

  // Restore PR_SET_DUMPABLE to its original value.
  if (prctl(PR_SET_DUMPABLE, orig_dumpable) != 0) {
    fatal_errno("failed to restore dumpable");
  }

  // Signals can either be fatal or nonfatal.
  // For fatal signals, crash_dump will PTRACE_CONT us with the signal we
  // crashed with, so that processes using waitpid on us will see that we
  // exited with the correct exit status (e.g. so that sh will report
  // "Segmentation fault" instead of "Killed"). For this to work, we need
  // to deregister our signal handler for that signal before continuing.
  if (signal_number != DEBUGGER_SIGNAL) {
    signal(signal_number, SIG_DFL);
  }

  resend_signal(info, thread_info.crash_dump_started);
  if (info->si_signo == DEBUGGER_SIGNAL) {
    // If the signal is fatal, don't unlock the mutex to prevent other crashing threads from
    // starting to dump right before our death.
    pthread_mutex_unlock(&crash_mutex);
  }
}

void debuggerd_init(debuggerd_callbacks_t* callbacks) {
  if (callbacks) {
    g_callbacks = *callbacks;
  }

  void* thread_stack_allocation =
    mmap(nullptr, PAGE_SIZE * 3, PROT_NONE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
  if (thread_stack_allocation == MAP_FAILED) {
    fatal_errno("failed to allocate debuggerd thread stack");
  }

  char* stack = static_cast<char*>(thread_stack_allocation) + PAGE_SIZE;
  if (mprotect(stack, PAGE_SIZE, PROT_READ | PROT_WRITE) != 0) {
    fatal_errno("failed to mprotect debuggerd thread stack");
  }

  // Stack grows negatively, set it to the last byte in the page...
  stack = (stack + PAGE_SIZE - 1);
  // and align it.
  stack -= 15;
  pseudothread_stack = stack;

  struct sigaction action;
  memset(&action, 0, sizeof(action));
  sigfillset(&action.sa_mask);
  action.sa_sigaction = debuggerd_signal_handler;
  action.sa_flags = SA_RESTART | SA_SIGINFO;

  // Use the alternate signal stack if available so we can catch stack overflows.
  action.sa_flags |= SA_ONSTACK;
  debuggerd_register_handlers(&action);
}