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35 #include "deduplicate.h"
36 #include <dynamic_config.h>
38 #include <logcommon.h>
39 #include "logconfig.h"
40 #include "loglimiter.h"
42 #define DEFAULT_CONFIG_LIMITER false
43 #define DEFAULT_CONFIG_PLOG true
44 #define DEFAULT_CONFIG_DEBUGMODE 0
45 #define DEFAULT_CONFIG_LIMITER_APPLY_TO_ALL_BUFFERS 0
48 * @brief Points to a function which writes a log message
49 * @details The function pointed to depends on the backend used
50 * @param[in] log_id ID of the buffer to log to. Belongs to (LOG_ID_INVALID, LOG_ID_MAX) non-inclusive
51 * @param[in] prio Priority of the message.
52 * @param[in] tag The message tag, identifies the sender.
53 * @param[in] msg The contents of the message.
54 * @return Returns the number of bytes written on success and a negative error value on error.
55 * @see __dlog_init_backend
57 int (*write_to_log)(log_id_t log_id, log_priority prio, const char *tag, const char *msg, struct timespec *tp_mono) = NULL;
58 void (*destroy_backend)();
60 int (*stash_failed_log)(log_id_t log_id, log_priority prio, const char *tag, const char *msg) = NULL;
62 static int stash_critical(log_id_t log_id, log_priority prio, const char *tag, const char *msg);
65 pthread_rwlock_t log_limiter_lock = PTHREAD_RWLOCK_INITIALIZER;
66 static pthread_mutex_t log_construction_lock = PTHREAD_MUTEX_INITIALIZER;
67 static bool is_initialized = false;
69 extern void __dlog_init_pipe(const struct log_config *conf);
70 extern void __dlog_init_android(const struct log_config *conf);
73 static bool dynamic_config;
74 static bool plog[LOG_ID_MAX];
75 static bool plog_default_values[LOG_ID_MAX];
76 static bool enable_secure_logs = true;
77 static bool enable_critical = true;
80 static int fatal_assert;
81 static int limiter_apply_to_all_buffers;
82 static _Atomic log_priority priority_filter_level = DLOG_VERBOSE;
84 static void __configure_limiter(struct log_config *config)
91 limiter = __log_limiter_create(config);
94 static int __configure_backend(struct log_config *config)
98 const char *const backend = log_config_get(config, "backend");
102 if (!strcmp(backend, "pipe"))
103 __dlog_init_pipe(config);
104 else if (!strcmp(backend, "logger"))
105 __dlog_init_android(config);
112 static void __set_plog_default_values()
114 for (size_t i = 0; i < NELEMS(plog); ++i)
115 plog_default_values[i] = plog[i];
118 static void __initialize_plog(const struct log_config *config)
122 const bool plog_default = log_config_get_boolean(config, "plog", DEFAULT_CONFIG_PLOG);
123 for (size_t i = 0; i < NELEMS(plog); ++i)
124 plog[i] = plog_default;
125 plog[LOG_ID_APPS] = true; // the default does not apply here for backward compatibility reasons.
126 __set_plog_default_values();
129 static void __configure_parameters(struct log_config *config)
133 __initialize_plog(config);
134 __update_plog(config);
135 __set_plog_default_values();
137 enable_secure_logs = log_config_get_boolean(config, "enable_secure_logs", enable_secure_logs);
138 enable_critical = log_config_get_boolean(config, "enable_critical", enable_critical);
139 debugmode = log_config_get_int(config, "debugmode", DEFAULT_CONFIG_DEBUGMODE);
140 fatal_assert = access(DEBUGMODE_FILE, F_OK) != -1;
141 limiter = log_config_get_boolean(config, "limiter", DEFAULT_CONFIG_LIMITER);
142 limiter_apply_to_all_buffers = log_config_get_int(config,
143 "limiter_apply_to_all_buffers",
144 DEFAULT_CONFIG_LIMITER_APPLY_TO_ALL_BUFFERS);
146 const char *stash_failed_log_method = log_config_get(config, "stash_failed_log_method");
147 if (stash_failed_log_method) {
149 if (strcmp(stash_failed_log_method, "critical") == 0)
150 stash_failed_log = stash_critical;
155 void __update_plog(const struct log_config *conf)
159 for (size_t i = 0; i < NELEMS(plog); ++i) {
160 char key[MAX_CONF_KEY_LEN];
161 const int r = snprintf(key, sizeof key, "enable_%s", log_name_by_id((log_id_t)i));
164 plog[i] = log_config_get_boolean(conf, key, plog_default_values[i]);
169 * @brief Configure the library
170 * @details Reads relevant config values
171 * @remarks This is more or less a constructor, but there are some obstacles
172 * to using it as such (i.e. with attribute constructor):
174 * - some important pieces of the system link to dlog, they start very early
175 * such that dlog can't properly initialize (which lasts for program lifetime)
176 * but don't actually log anything until later on and would be fine under lazy
177 * initialisation. The way to do it "properly" would be to expose this function
178 * into the API so that people can manually call it when they're ready, but
179 * one of the design goals of the current API is that it requires absolutely no
180 * other calls than `dlog_print`. Changing it would require somebody with a
181 * bird's eye view of the system to produce a design so I wouldn't count on it.
183 * - the constructor would need to have as high of a priority as possible (so as
184 * to minimize the risk of another library's constructor using uninitialized data)
185 * but at the same time others might want some room to wrap functions before
186 * dlog uses them (think mprobe/mcheck). This would also require a design pass.
191 bool __configure(void)
193 __attribute__((cleanup(log_config_free))) struct log_config config;
195 if (log_config_read(&config) < 0)
198 dynamic_config = __dynamic_config_create(&config);
200 __configure_parameters(&config);
202 if (!__configure_backend(&config)) {
203 __dynamic_config_destroy();
204 dynamic_config = false;
208 __configure_deduplicate(&config);
209 __configure_limiter(&config);
213 static void __attribute__((constructor(101))) __install_pipe_handler(void)
215 /* We mask SIGPIPE signal because most applications do not install their
216 * own SIGPIPE handler. Default behaviour in SIGPIPE case is to abort the
217 * process. SIGPIPE occurs when e.g. dlog daemon closes read pipe endpoint.
219 * We do this in the library constructor (at maximum priority) and not
220 * during regular (lazy) initialisation so as to prevent overwriting the
221 * program's actual signal handler, if it has one.
223 * In theory this is not required for the Android logger backend; however,
224 * this early we don't yet know the backend and also it is good to behave
225 * consistently in this regard anyway.
227 * We don't revert this in a destructor because Unix signals are bonkers
228 * and we have no way to do this cleanly. Most libdlog users don't use
229 * runtime linking so this would mostly done at program exit either way. */
230 signal(SIGPIPE, SIG_IGN);
233 static bool first = true;
234 static bool initialize()
239 /* The mutex acts as a barrier, but otherwise the C language's
240 * machine abstraction is single-threaded. This means that the
241 * compiler is free to rearrange calls inside the mutex according
242 * to the as-if rule because it doesn't care if another thread can
243 * access it in parallel. In particular, `is_initialized = true`
244 * directly after `__configure()` could be rearranged to go in
245 * front of it because it is not touched inside that function
246 * if the compiler thinks it helps somehow (not unlikely: since
247 * it is checked before the mutex, it is very probable for it to
248 * still be in the CPU register or something like that). On top
249 * of that, some architectures (in particular, armv7l) don't have
250 * strict memory guarantees and can reorder actual memory stores
251 * on their own, even if the compiler didn't do anything fancy
252 * when creating machine code. For more info about the issue,
253 * see https://www.aristeia.com/Papers/DDJ_Jul_Aug_2004_revised.pdf
255 * Ultimately this means that there needs to be some sort of
256 * barrier between `__configure` and `is_initialized = true`,
257 * and the simplest way to achieve that is to just wait until
258 * the second entry into the mutex. */
261 pthread_mutex_lock(&log_construction_lock);
263 first = !__configure();
265 is_initialized = true;
267 pthread_mutex_unlock(&log_construction_lock);
272 * @brief Fatal assertion
273 * @details Conditionally crash the sucka who sent the log
274 * @param[in] prio Priority of the log
276 static void __dlog_fatal_assert(int prio)
278 assert(!fatal_assert || (prio != DLOG_FATAL));
282 * @brief Check log validity
283 * @details Checks whether the log is valid and eligible for printing
284 * @param[in] log_id The target buffer ID
285 * @param[in] prio The log's priority
286 * @param[in] tag The log's tag
287 * @return DLOG_ERROR_NONE on success, else an error code.
288 * @retval DLOG_ERROR_INVALID_PARAMETER Invalid parameter
290 static int dlog_check_validity(log_id_t log_id, int prio, const char *tag)
294 return DLOG_ERROR_INVALID_PARAMETER;
296 if (log_id <= LOG_ID_INVALID || LOG_ID_MAX <= log_id)
297 return DLOG_ERROR_INVALID_PARAMETER;
299 return DLOG_ERROR_NONE;
303 * @brief Check log against limiter rules
304 * @details Checks whether the log passes current limiter rules
305 * @param[in] log_id The target buffer ID
306 * @param[in] prio The log's priority
307 * @param[in] tag The log's tag
308 * @return DLOG_ERROR_NONE on success, else an error code.
309 * @retval DLOG_ERROR_NOT_PERMITTED Not permitted
311 static int dlog_check_limiter(log_id_t log_id, int prio, const char *tag)
313 if (!debugmode && prio <= DLOG_DEBUG)
314 return DLOG_ERROR_NOT_PERMITTED;
317 __dynamic_config_update();
320 struct pass_log_result should_log = { .decision = DECISION_DENIED };
321 if (!pthread_rwlock_rdlock(&log_limiter_lock)) {
322 should_log = __log_limiter_pass_log(tag, prio);
323 pthread_rwlock_unlock(&log_limiter_lock);
326 switch (should_log.decision) {
327 case DECISION_DENIED:
328 return DLOG_ERROR_NOT_PERMITTED;
330 case DECISION_TAG_LIMIT_EXCEEDED_MESSAGE:
331 case DECISION_PID_LIMIT_EXCEEDED_MESSAGE: {
333 int result = clock_gettime(CLOCK_MONOTONIC, &tp);
335 return DLOG_ERROR_NOT_PERMITTED;
337 snprintf(buf, sizeof(buf),
338 "Your log has been blocked due to per-%s limit of %d logs per %d seconds.",
339 should_log.decision == DECISION_TAG_LIMIT_EXCEEDED_MESSAGE ? "tag" : "PID",
340 should_log.logs_per_period, should_log.period_s);
341 write_to_log(log_id, prio, tag, buf, &tp);
342 return DLOG_ERROR_NOT_PERMITTED;
345 case DECISION_ALLOWED:
350 /* This can change due to __dynamic_config_update(), but is atomic and its
351 * value implies nothing else so does not need to be under a lock. */
353 return DLOG_ERROR_NOT_PERMITTED;
355 return DLOG_ERROR_NONE;
358 static int __write_to_log_critical_section(log_id_t log_id, int prio, const char *tag, const char *fmt, va_list ap, bool check_should_log)
360 if (check_should_log && prio < priority_filter_level)
361 return DLOG_ERROR_NONE;
363 if ((check_should_log || limiter_apply_to_all_buffers) && (dlog_check_limiter(log_id, prio, tag) < 0))
364 return DLOG_ERROR_NONE;
366 char buf[LOG_MAX_PAYLOAD_SIZE];
367 int len = vsnprintf(buf, sizeof buf, fmt, ap);
369 return DLOG_ERROR_NONE;
370 else if (len >= sizeof buf)
371 len = sizeof buf - 1;
375 if (deduplicate_func && !clock_gettime(CLOCK_MONOTONIC, &tp)) {
376 dlog_deduplicate_e ret = deduplicate_func(buf, len, &tp);
377 if (ret == DLOG_DEDUPLICATE)
378 return DLOG_ERROR_NONE;
379 else if (ret == DLOG_DO_NOT_DEDUPLICATE_BUT_WARN)
380 deduplicate_warn(buf, sizeof buf, len);
381 r = write_to_log(log_id, prio, tag, buf, &tp);
383 r = write_to_log(log_id, prio, tag, buf, NULL);
385 if (r < 0 && stash_failed_log)
386 r = stash_failed_log(log_id, prio, tag, buf);
391 static int __write_to_log(log_id_t log_id, int prio, const char *tag, const char *fmt, va_list ap, bool check_should_log, bool secure_log)
393 int ret = dlog_check_validity(log_id, prio, tag);
397 /* Threads can be cancelled before they give up a lock.
398 * Therefore cancellation is temporarily disabled.
399 * This solution is comparatively simple and cheap.
400 * The other solutions (cleanup handlers, robust mutexes)
401 * would be much more complicated and also inflict larger
402 * runtime costs. The downside of disabling cancellation
403 * is not a problem in our case because it is temporary
404 * and very brief so we don't keep an obsolete thread
405 * for much longer than we otherwise would. */
406 int old_cancel_state;
407 pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &old_cancel_state);
409 /* The only thing that needs to be protected here is `write_to_log` since
410 * all other resources already have their own specific locks (and even the
411 * pointer could be made to point at a null handler instead of a true NULL)
412 * but giving this guarantee makes everything a lot simpler as it removes
413 * the risk of something suddenly becoming NULL during processing. */
414 if (!initialize() || !write_to_log)
415 // TODO: We could consider stashing the failed log here
416 ret = DLOG_ERROR_NOT_PERMITTED;
417 else if (secure_log && !enable_secure_logs)
420 ret = __write_to_log_critical_section(log_id, prio, tag, fmt, ap, check_should_log);
422 pthread_setcancelstate(old_cancel_state, NULL);
427 int __critical_log_append_timestamp(char *buf, size_t buflen)
429 /* NB: the timestamp may slightly differ from the one that gets
430 * added onto the copy that goes into the regular buffer, and
431 * timestamp acquisition is duplicated. This would ideally be
432 * solved, but timestamps are currently added fairly deep in
433 * backend-specific functions so for now this will have to do.
434 * Also, since we're the sender, there is just this one set of
435 * timestamps, i.e. the send timestamp! The usual alternative
436 * set of receive timestamps will never have the opportunity
437 * to get added to the entry since this log is supposed to end
438 * up straight in the file (there's potentially the trusted
439 * writer binary but we're trying to keep the set of actions
440 * it needs to do to the minimum and those timestamps would
441 * in practice be the same anyway). */
444 clock_gettime(CLOCK_REALTIME, &ts);
445 const time_t tt = ts.tv_sec;
446 const long int real_millisec = ts.tv_nsec / 1000000;
447 clock_gettime(CLOCK_MONOTONIC, &ts);
449 struct tm *const ptm = localtime_r(&tt, &tmBuf);
450 assert(ptm); // we're in a short lived fork so asserts are fine and make things simple
452 int len = strftime(buf, buflen, "%m-%d %H:%M:%S", ptm);
455 int tmp_len = snprintf(buf + len, buflen - len, ".%03ld", real_millisec);
457 assert(tmp_len < buflen - len);
460 tmp_len = strftime(buf + len, buflen - len, "%z ", ptm);
461 assert(tmp_len != 0);
464 tmp_len = snprintf(buf + len, buflen - len, "%5lu.%03ld", ts.tv_sec, ts.tv_nsec / 1000000);
466 assert(tmp_len < buflen - len);
472 int __critical_log_build_msg(char *buf, size_t buflen, pid_t main_pid, pid_t main_tid, log_id_t log_id, int prio, const char *tag, const char *fmt, va_list ap)
474 int len = __critical_log_append_timestamp(buf, buflen);
475 const int metadata_len = snprintf(buf + len, buflen - len, " P%5d T%5d B%-6s %c/%-8s: ",
478 log_name_by_id(log_id),
479 filter_pri_to_char(prio),
480 tag ?: "CRITICAL_NO_TAG");
481 assert(metadata_len > 0);
482 if (metadata_len >= buflen - len)
483 return buflen - 1; // can genuinely happen with an exceedingly large tag
486 const int content_len = vsnprintf(buf + len, buflen - len, fmt, ap);
487 assert(content_len >= 0); // 0 is legit with format == ""
488 if (content_len >= buflen - len)
496 __attribute__ ((noreturn))
498 void __critical_log_child(pid_t main_pid, pid_t main_tid, log_id_t log_id, int prio, const char *tag, const char *fmt, va_list ap)
500 char buf[LOG_MAX_PAYLOAD_SIZE + 128]; // extra space for some metadata
501 const int len = __critical_log_build_msg(buf, sizeof buf - 1, main_pid, main_tid, log_id, prio, tag, fmt, ap);
505 static const char *const path = "/usr/libexec/dlog-log-critical";
506 execl(path, path /* argv[0] convention */, buf, (char *) NULL);
509 /* Compilers are sometimes smart enough to recognize _exit's
510 * noreturn attribute, even if we wrap it with something that
511 * returns. This causes it to behave in unexpected ways, for
512 * example it can blow up the program regardless or it can
513 * optimize some conditionals out (and incorrectly enter them
514 * after the exit call fails to actually exit). This makes it
515 * unsuitable for tests. */
517 _exit(1); // not the regular `exit` so as not to trigger any `atexit` handlers prematurely
521 #ifndef UNIT_TEST // contains forks and exits, these don't work well with wrapping (see above)
522 void __critical_log(log_id_t log_id, int prio, const char *tag, const char *fmt, va_list ap)
524 /* Critical log functionality is mostly done in a separate binary
525 * to handle security correctly (else every process would have to
526 * possess the necessary privilege to write onto that file, which
527 * would be opening a fairly nasty can of worms from the security
528 * point of view). Our use of exec() is why a simple thread would
529 * not suffice and we're resorting to a fork.
531 * The double fork, much like a double barreled 12 gauge shotgun,
532 * is an elegant solution designed to stop a zombie army. We'd be
533 * creating zombie processes if we didn't wait() for the children
534 * we spawn, but we don't really want to do that since it results
535 * in a needless delay. Instead, the writer process is actually a
536 * grandchild, with our direct child exiting immediately just for
537 * us to have something to wait on that is guaranteed not to take
538 * too long. The orphaned grandchild is adopted by init, who will
539 * take care to reap it when it dies. In addition to avoiding the
540 * delay, the client will not have any unexpected children (which
541 * could ruin logic in its own waits).
544 * ┌───────┐ ┌─────────┐ ┌─────────────┐ ┌────────┐
545 * │ pid 1 ├──>│ libdlog ├──>│ immediately ├──>│ execs │
546 * │ init │ │ client │ │ exits │ │ writer │
547 * └───────┘ └─────────┘ └─────────────┘ └────────┘
549 * Afterwards, libdlog has no children:
550 * ┌───────┐ ┌─────────┐ ┌────────┐
551 * │ pid 1 ├──>│ libdlog │ ┌─────────>│ writer │
552 * │ init ├─┐ │ client │ │ │ binary │
553 * └───────┘ │ └─────────┘ │ └────────┘
554 * └──────────────────────┘
559 if (!enable_critical)
562 const pid_t main_pid = getpid();
563 const pid_t main_tid = gettid();
565 const int temporary_exiter_pid = fork();
566 if (temporary_exiter_pid < 0)
568 if (temporary_exiter_pid != 0) {
569 waitpid(temporary_exiter_pid, NULL, 0);
573 const int child_pid = fork();
579 __critical_log_child(main_pid, main_tid, log_id, prio, tag, fmt, ap);
582 static void stash_critical_inner(log_id_t log_id, log_priority prio, const char *tag, const char *fmt, ...)
587 __critical_log(log_id, prio, tag, fmt, ap);
591 static int stash_critical(log_id_t log_id, log_priority prio, const char *tag, const char *msg)
593 stash_critical_inner(log_id, prio, tag, "FAILED TO LOG: %s", msg);
597 int __dlog_critical_print(log_id_t log_id, int prio, const char *tag, const char *fmt, ...)
602 __critical_log(log_id, prio, tag, fmt, ap);
606 int ret = __dlog_vprint(log_id, prio, tag, fmt, ap);
613 int dlog_set_minimum_priority(int priority)
615 if (priority < DLOG_DEFAULT || priority > DLOG_PRIO_MAX)
616 return DLOG_ERROR_INVALID_PARAMETER;
618 priority_filter_level = priority;
619 return DLOG_ERROR_NONE;
624 * @details Print a log line
625 * @param[in] log_id The target buffer ID
626 * @param[in] prio Priority
628 * @param[in] fmt Format (same as printf)
629 * @param[in] ap Argument list
630 * @return Bytes written, or negative error
632 int __dlog_vprint(log_id_t log_id, int prio, const char *tag, const char *fmt, va_list ap)
634 int ret = __write_to_log(log_id, prio, tag, fmt, ap, true, false);
635 __dlog_fatal_assert(prio);
642 * @details Print a log line
643 * @param[in] log_id The target buffer ID
644 * @param[in] prio Priority
646 * @param[in] fmt Format (same as printf)
647 * @return Bytes written, or negative error
649 int __dlog_print(log_id_t log_id, int prio, const char *tag, const char *fmt, ...)
654 int ret = __dlog_vprint(log_id, prio, tag, fmt, ap);
662 * @details Print a log line
663 * @param[in] log_id The target buffer ID
664 * @param[in] prio Priority
666 * @param[in] fmt Format (same as printf)
667 * @return Bytes written, or negative error
669 int __dlog_sec_print(log_id_t log_id, int prio, const char *tag, const char *fmt, ...)
671 if (!enable_secure_logs)
677 int ret = __write_to_log(log_id, prio, tag, fmt, ap, true, true);
678 __dlog_fatal_assert(prio);
684 int dlog_vprint(log_priority prio, const char *tag, const char *fmt, va_list ap)
686 return __write_to_log(LOG_ID_APPS, prio, tag, fmt, ap, false, false);
689 int dlog_print(log_priority prio, const char *tag, const char *fmt, ...)
694 int ret = dlog_vprint(prio, tag, fmt, ap);
701 * @brief Finalize DLog
702 * @details Finalizes and deallocates the library
703 * @notes Used directly in tests; brings back the pre-init state
705 void __dlog_fini(void)
707 if (destroy_backend) {
709 destroy_backend = NULL;
712 is_initialized = false;
715 enable_secure_logs = true;
716 enable_critical = false;
717 __deduplicate_destroy();
718 __log_limiter_destroy();
719 __dynamic_config_destroy();