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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;
79 static int fatal_assert;
80 static int limiter_apply_to_all_buffers;
81 static _Atomic log_priority priority_filter_level = DLOG_VERBOSE;
83 static void __configure_limiter(struct log_config *config)
90 limiter = __log_limiter_create(config);
93 static int __configure_backend(struct log_config *config)
97 const char *const backend = log_config_get(config, "backend");
101 if (!strcmp(backend, "pipe"))
102 __dlog_init_pipe(config);
103 else if (!strcmp(backend, "logger"))
104 __dlog_init_android(config);
111 static void __set_plog_default_values()
113 for (size_t i = 0; i < NELEMS(plog); ++i)
114 plog_default_values[i] = plog[i];
117 static void __initialize_plog(const struct log_config *config)
121 const bool plog_default = log_config_get_boolean(config, "plog", DEFAULT_CONFIG_PLOG);
122 for (size_t i = 0; i < NELEMS(plog); ++i)
123 plog[i] = plog_default;
124 plog[LOG_ID_APPS] = true; // the default does not apply here for backward compatibility reasons.
125 __set_plog_default_values();
128 static void __configure_parameters(struct log_config *config)
132 __initialize_plog(config);
133 __update_plog(config);
134 __set_plog_default_values();
136 enable_secure_logs = log_config_get_boolean(config, "enable_secure_logs", enable_secure_logs);
137 debugmode = log_config_get_int(config, "debugmode", DEFAULT_CONFIG_DEBUGMODE);
138 fatal_assert = access(DEBUGMODE_FILE, F_OK) != -1;
139 limiter = log_config_get_boolean(config, "limiter", DEFAULT_CONFIG_LIMITER);
140 limiter_apply_to_all_buffers = log_config_get_int(config,
141 "limiter_apply_to_all_buffers",
142 DEFAULT_CONFIG_LIMITER_APPLY_TO_ALL_BUFFERS);
144 const char *stash_failed_log_method = log_config_get(config, "stash_failed_log_method");
145 if (stash_failed_log_method) {
147 if (strcmp(stash_failed_log_method, "critical") == 0)
148 stash_failed_log = stash_critical;
153 void __update_plog(const struct log_config *conf)
157 for (size_t i = 0; i < NELEMS(plog); ++i) {
158 char key[MAX_CONF_KEY_LEN];
159 const int r = snprintf(key, sizeof key, "enable_%s", log_name_by_id((log_id_t)i));
162 plog[i] = log_config_get_boolean(conf, key, plog_default_values[i]);
167 * @brief Configure the library
168 * @details Reads relevant config values
169 * @remarks This is more or less a constructor, but there are some obstacles
170 * to using it as such (i.e. with attribute constructor):
172 * - some important pieces of the system link to dlog, they start very early
173 * such that dlog can't properly initialize (which lasts for program lifetime)
174 * but don't actually log anything until later on and would be fine under lazy
175 * initialisation. The way to do it "properly" would be to expose this function
176 * into the API so that people can manually call it when they're ready, but
177 * one of the design goals of the current API is that it requires absolutely no
178 * other calls than `dlog_print`. Changing it would require somebody with a
179 * bird's eye view of the system to produce a design so I wouldn't count on it.
181 * - the constructor would need to have as high of a priority as possible (so as
182 * to minimize the risk of another library's constructor using uninitialized data)
183 * but at the same time others might want some room to wrap functions before
184 * dlog uses them (think mprobe/mcheck). This would also require a design pass.
189 bool __configure(void)
191 __attribute__((cleanup(log_config_free))) struct log_config config;
193 if (log_config_read(&config) < 0)
196 dynamic_config = __dynamic_config_create(&config);
198 __configure_parameters(&config);
200 if (!__configure_backend(&config)) {
201 __dynamic_config_destroy();
202 dynamic_config = false;
206 __configure_deduplicate(&config);
207 __configure_limiter(&config);
211 static void __attribute__((constructor(101))) __install_pipe_handler(void)
213 /* We mask SIGPIPE signal because most applications do not install their
214 * own SIGPIPE handler. Default behaviour in SIGPIPE case is to abort the
215 * process. SIGPIPE occurs when e.g. dlog daemon closes read pipe endpoint.
217 * We do this in the library constructor (at maximum priority) and not
218 * during regular (lazy) initialisation so as to prevent overwriting the
219 * program's actual signal handler, if it has one.
221 * In theory this is not required for the Android logger backend; however,
222 * this early we don't yet know the backend and also it is good to behave
223 * consistently in this regard anyway.
225 * We don't revert this in a destructor because Unix signals are bonkers
226 * and we have no way to do this cleanly. Most libdlog users don't use
227 * runtime linking so this would mostly done at program exit either way. */
228 signal(SIGPIPE, SIG_IGN);
231 static bool first = true;
232 static bool initialize()
237 /* The mutex acts as a barrier, but otherwise the C language's
238 * machine abstraction is single-threaded. This means that the
239 * compiler is free to rearrange calls inside the mutex according
240 * to the as-if rule because it doesn't care if another thread can
241 * access it in parallel. In particular, `is_initialized = true`
242 * directly after `__configure()` could be rearranged to go in
243 * front of it because it is not touched inside that function
244 * if the compiler thinks it helps somehow (not unlikely: since
245 * it is checked before the mutex, it is very probable for it to
246 * still be in the CPU register or something like that). On top
247 * of that, some architectures (in particular, armv7l) don't have
248 * strict memory guarantees and can reorder actual memory stores
249 * on their own, even if the compiler didn't do anything fancy
250 * when creating machine code. For more info about the issue,
251 * see https://www.aristeia.com/Papers/DDJ_Jul_Aug_2004_revised.pdf
253 * Ultimately this means that there needs to be some sort of
254 * barrier between `__configure` and `is_initialized = true`,
255 * and the simplest way to achieve that is to just wait until
256 * the second entry into the mutex. */
259 pthread_mutex_lock(&log_construction_lock);
261 first = !__configure();
263 is_initialized = true;
265 pthread_mutex_unlock(&log_construction_lock);
270 * @brief Fatal assertion
271 * @details Conditionally crash the sucka who sent the log
272 * @param[in] prio Priority of the log
274 static void __dlog_fatal_assert(int prio)
276 assert(!fatal_assert || (prio != DLOG_FATAL));
280 * @brief Check log validity
281 * @details Checks whether the log is valid and eligible for printing
282 * @param[in] log_id The target buffer ID
283 * @param[in] prio The log's priority
284 * @param[in] tag The log's tag
285 * @return DLOG_ERROR_NONE on success, else an error code.
286 * @retval DLOG_ERROR_INVALID_PARAMETER Invalid parameter
288 static int dlog_check_validity(log_id_t log_id, int prio, const char *tag)
292 return DLOG_ERROR_INVALID_PARAMETER;
294 if (log_id <= LOG_ID_INVALID || LOG_ID_MAX <= log_id)
295 return DLOG_ERROR_INVALID_PARAMETER;
297 return DLOG_ERROR_NONE;
301 * @brief Check log against limiter rules
302 * @details Checks whether the log passes current limiter rules
303 * @param[in] log_id The target buffer ID
304 * @param[in] prio The log's priority
305 * @param[in] tag The log's tag
306 * @return DLOG_ERROR_NONE on success, else an error code.
307 * @retval DLOG_ERROR_NOT_PERMITTED Not permitted
309 static int dlog_check_limiter(log_id_t log_id, int prio, const char *tag)
311 if (!debugmode && prio <= DLOG_DEBUG)
312 return DLOG_ERROR_NOT_PERMITTED;
315 __dynamic_config_update();
318 struct pass_log_result should_log = { .decision = DECISION_DENIED };
319 if (!pthread_rwlock_rdlock(&log_limiter_lock)) {
320 should_log = __log_limiter_pass_log(tag, prio);
321 pthread_rwlock_unlock(&log_limiter_lock);
324 switch (should_log.decision) {
325 case DECISION_DENIED:
326 return DLOG_ERROR_NOT_PERMITTED;
328 case DECISION_TAG_LIMIT_EXCEEDED_MESSAGE:
329 case DECISION_PID_LIMIT_EXCEEDED_MESSAGE: {
331 int result = clock_gettime(CLOCK_MONOTONIC, &tp);
333 return DLOG_ERROR_NOT_PERMITTED;
335 snprintf(buf, sizeof(buf),
336 "Your log has been blocked due to per-%s limit of %d logs per %d seconds.",
337 should_log.decision == DECISION_TAG_LIMIT_EXCEEDED_MESSAGE ? "tag" : "PID",
338 should_log.logs_per_period, should_log.period_s);
339 write_to_log(log_id, prio, tag, buf, &tp);
340 return DLOG_ERROR_NOT_PERMITTED;
343 case DECISION_ALLOWED:
348 /* This can change due to __dynamic_config_update(), but is atomic and its
349 * value implies nothing else so does not need to be under a lock. */
351 return DLOG_ERROR_NOT_PERMITTED;
353 return DLOG_ERROR_NONE;
356 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)
358 if (check_should_log && prio < priority_filter_level)
359 return DLOG_ERROR_NONE;
361 if ((check_should_log || limiter_apply_to_all_buffers) && (dlog_check_limiter(log_id, prio, tag) < 0))
362 return DLOG_ERROR_NONE;
364 char buf[LOG_MAX_PAYLOAD_SIZE];
365 int len = vsnprintf(buf, sizeof buf, fmt, ap);
367 return DLOG_ERROR_NONE;
368 else if (len >= sizeof buf)
369 len = sizeof buf - 1;
373 if (deduplicate_func && !clock_gettime(CLOCK_MONOTONIC, &tp)) {
374 dlog_deduplicate_e ret = deduplicate_func(buf, len, &tp);
375 if (ret == DLOG_DEDUPLICATE)
376 return DLOG_ERROR_NONE;
377 else if (ret == DLOG_DO_NOT_DEDUPLICATE_BUT_WARN)
378 deduplicate_warn(buf, sizeof buf, len);
379 r = write_to_log(log_id, prio, tag, buf, &tp);
381 r = write_to_log(log_id, prio, tag, buf, NULL);
383 if (r < 0 && stash_failed_log)
384 r = stash_failed_log(log_id, prio, tag, buf);
389 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)
391 int ret = dlog_check_validity(log_id, prio, tag);
395 /* Threads can be cancelled before they give up a lock.
396 * Therefore cancellation is temporarily disabled.
397 * This solution is comparatively simple and cheap.
398 * The other solutions (cleanup handlers, robust mutexes)
399 * would be much more complicated and also inflict larger
400 * runtime costs. The downside of disabling cancellation
401 * is not a problem in our case because it is temporary
402 * and very brief so we don't keep an obsolete thread
403 * for much longer than we otherwise would. */
404 int old_cancel_state;
405 pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &old_cancel_state);
407 /* The only thing that needs to be protected here is `write_to_log` since
408 * all other resources already have their own specific locks (and even the
409 * pointer could be made to point at a null handler instead of a true NULL)
410 * but giving this guarantee makes everything a lot simpler as it removes
411 * the risk of something suddenly becoming NULL during processing. */
412 if (!initialize() || !write_to_log)
413 // TODO: We could consider stashing the failed log here
414 ret = DLOG_ERROR_NOT_PERMITTED;
415 else if (secure_log && !enable_secure_logs)
418 ret = __write_to_log_critical_section(log_id, prio, tag, fmt, ap, check_should_log);
420 pthread_setcancelstate(old_cancel_state, NULL);
425 int __critical_log_append_timestamp(char *buf, size_t buflen)
427 /* NB: the timestamp may slightly differ from the one that gets
428 * added onto the copy that goes into the regular buffer, and
429 * timestamp acquisition is duplicated. This would ideally be
430 * solved, but timestamps are currently added fairly deep in
431 * backend-specific functions so for now this will have to do.
432 * Also, since we're the sender, there is just this one set of
433 * timestamps, i.e. the send timestamp! The usual alternative
434 * set of receive timestamps will never have the opportunity
435 * to get added to the entry since this log is supposed to end
436 * up straight in the file (there's potentially the trusted
437 * writer binary but we're trying to keep the set of actions
438 * it needs to do to the minimum and those timestamps would
439 * in practice be the same anyway). */
442 clock_gettime(CLOCK_REALTIME, &ts);
443 const time_t tt = ts.tv_sec;
444 const long int real_millisec = ts.tv_nsec / 1000000;
445 clock_gettime(CLOCK_MONOTONIC, &ts);
447 struct tm *const ptm = localtime_r(&tt, &tmBuf);
448 assert(ptm); // we're in a short lived fork so asserts are fine and make things simple
450 int len = strftime(buf, buflen, "%m-%d %H:%M:%S", ptm);
453 int tmp_len = snprintf(buf + len, buflen - len, ".%03ld", real_millisec);
455 assert(tmp_len < buflen - len);
458 tmp_len = strftime(buf + len, buflen - len, "%z ", ptm);
459 assert(tmp_len != 0);
462 tmp_len = snprintf(buf + len, buflen - len, "%5lu.%03ld", ts.tv_sec, ts.tv_nsec / 1000000);
464 assert(tmp_len < buflen - len);
470 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)
472 int len = __critical_log_append_timestamp(buf, buflen);
473 const int metadata_len = snprintf(buf + len, buflen - len, " P%5d T%5d B%-6s %c/%-8s: ",
476 log_name_by_id(log_id),
477 filter_pri_to_char(prio),
478 tag ?: "CRITICAL_NO_TAG");
479 assert(metadata_len > 0);
480 if (metadata_len >= buflen - len)
481 return buflen - 1; // can genuinely happen with an exceedingly large tag
484 const int content_len = vsnprintf(buf + len, buflen - len, fmt, ap);
485 assert(content_len >= 0); // 0 is legit with format == ""
486 if (content_len >= buflen - len)
494 __attribute__ ((noreturn))
496 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)
498 char buf[LOG_MAX_PAYLOAD_SIZE + 128]; // extra space for some metadata
499 const int len = __critical_log_build_msg(buf, sizeof buf - 1, main_pid, main_tid, log_id, prio, tag, fmt, ap);
503 static const char *const path = "/usr/libexec/dlog-log-critical";
504 execl(path, path /* argv[0] convention */, buf, (char *) NULL);
507 /* Compilers are sometimes smart enough to recognize _exit's
508 * noreturn attribute, even if we wrap it with something that
509 * returns. This causes it to behave in unexpected ways, for
510 * example it can blow up the program regardless or it can
511 * optimize some conditionals out (and incorrectly enter them
512 * after the exit call fails to actually exit). This makes it
513 * unsuitable for tests. */
515 _exit(1); // not the regular `exit` so as not to trigger any `atexit` handlers prematurely
519 #ifndef UNIT_TEST // contains forks and exits, these don't work well with wrapping (see above)
520 void __critical_log(log_id_t log_id, int prio, const char *tag, const char *fmt, va_list ap)
522 /* Critical log functionality is mostly done in a separate binary
523 * to handle security correctly (else every process would have to
524 * possess the necessary privilege to write onto that file, which
525 * would be opening a fairly nasty can of worms from the security
526 * point of view). Our use of exec() is why a simple thread would
527 * not suffice and we're resorting to a fork.
529 * The double fork, much like a double barreled 12 gauge shotgun,
530 * is an elegant solution designed to stop a zombie army. We'd be
531 * creating zombie processes if we didn't wait() for the children
532 * we spawn, but we don't really want to do that since it results
533 * in a needless delay. Instead, the writer process is actually a
534 * grandchild, with our direct child exiting immediately just for
535 * us to have something to wait on that is guaranteed not to take
536 * too long. The orphaned grandchild is adopted by init, who will
537 * take care to reap it when it dies. In addition to avoiding the
538 * delay, the client will not have any unexpected children (which
539 * could ruin logic in its own waits).
542 * ┌───────┐ ┌─────────┐ ┌─────────────┐ ┌────────┐
543 * │ pid 1 ├──>│ libdlog ├──>│ immediately ├──>│ execs │
544 * │ init │ │ client │ │ exits │ │ writer │
545 * └───────┘ └─────────┘ └─────────────┘ └────────┘
547 * Afterwards, libdlog has no children:
548 * ┌───────┐ ┌─────────┐ ┌────────┐
549 * │ pid 1 ├──>│ libdlog │ ┌─────────>│ writer │
550 * │ init ├─┐ │ client │ │ │ binary │
551 * └───────┘ │ └─────────┘ │ └────────┘
552 * └──────────────────────┘
555 const pid_t main_pid = getpid();
556 const pid_t main_tid = gettid();
558 const int temporary_exiter_pid = fork();
559 if (temporary_exiter_pid < 0)
561 if (temporary_exiter_pid != 0) {
562 waitpid(temporary_exiter_pid, NULL, 0);
566 const int child_pid = fork();
572 __critical_log_child(main_pid, main_tid, log_id, prio, tag, fmt, ap);
575 static void stash_critical_inner(log_id_t log_id, log_priority prio, const char *tag, const char *fmt, ...)
580 __critical_log(log_id, prio, tag, fmt, ap);
584 static int stash_critical(log_id_t log_id, log_priority prio, const char *tag, const char *msg)
586 stash_critical_inner(log_id, prio, tag, "FAILED TO LOG: %s", msg);
590 int __dlog_critical_print(log_id_t log_id, int prio, const char *tag, const char *fmt, ...)
595 __critical_log(log_id, prio, tag, fmt, ap);
599 int ret = __dlog_vprint(log_id, prio, tag, fmt, ap);
606 int dlog_set_minimum_priority(int priority)
608 if (priority < DLOG_DEFAULT || priority > DLOG_PRIO_MAX)
609 return DLOG_ERROR_INVALID_PARAMETER;
611 priority_filter_level = priority;
612 return DLOG_ERROR_NONE;
617 * @details Print a log line
618 * @param[in] log_id The target buffer ID
619 * @param[in] prio Priority
621 * @param[in] fmt Format (same as printf)
622 * @param[in] ap Argument list
623 * @return Bytes written, or negative error
625 int __dlog_vprint(log_id_t log_id, int prio, const char *tag, const char *fmt, va_list ap)
627 int ret = __write_to_log(log_id, prio, tag, fmt, ap, true, false);
628 __dlog_fatal_assert(prio);
635 * @details Print a log line
636 * @param[in] log_id The target buffer ID
637 * @param[in] prio Priority
639 * @param[in] fmt Format (same as printf)
640 * @return Bytes written, or negative error
642 int __dlog_print(log_id_t log_id, int prio, const char *tag, const char *fmt, ...)
647 int ret = __dlog_vprint(log_id, prio, tag, fmt, ap);
655 * @details Print a log line
656 * @param[in] log_id The target buffer ID
657 * @param[in] prio Priority
659 * @param[in] fmt Format (same as printf)
660 * @return Bytes written, or negative error
662 int __dlog_sec_print(log_id_t log_id, int prio, const char *tag, const char *fmt, ...)
664 if (!enable_secure_logs)
670 int ret = __write_to_log(log_id, prio, tag, fmt, ap, true, true);
671 __dlog_fatal_assert(prio);
677 int dlog_vprint(log_priority prio, const char *tag, const char *fmt, va_list ap)
679 return __write_to_log(LOG_ID_APPS, prio, tag, fmt, ap, false, false);
682 int dlog_print(log_priority prio, const char *tag, const char *fmt, ...)
687 int ret = dlog_vprint(prio, tag, fmt, ap);
694 * @brief Finalize DLog
695 * @details Finalizes and deallocates the library
696 * @notes Used directly in tests; brings back the pre-init state
698 void __dlog_fini(void)
700 if (destroy_backend) {
702 destroy_backend = NULL;
705 is_initialized = false;
708 enable_secure_logs = true;
709 __deduplicate_destroy();
710 __log_limiter_destroy();
711 __dynamic_config_destroy();