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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 pthread_rwlock_t log_limiter_lock = PTHREAD_RWLOCK_INITIALIZER;
61 static pthread_mutex_t log_construction_lock = PTHREAD_MUTEX_INITIALIZER;
62 static bool is_initialized = false;
64 extern void __dlog_init_pipe(const struct log_config *conf);
65 extern void __dlog_init_android(const struct log_config *conf);
68 static bool dynamic_config;
69 static bool plog[LOG_ID_MAX];
70 static bool plog_default_values[LOG_ID_MAX];
71 static bool enable_secure_logs = true;
74 static int fatal_assert;
75 static int limiter_apply_to_all_buffers;
76 static _Atomic log_priority priority_filter_level = DLOG_VERBOSE;
78 static void __configure_limiter(struct log_config *config)
85 limiter = __log_limiter_create(config);
88 static int __configure_backend(struct log_config *config)
92 const char *const backend = log_config_get(config, "backend");
96 if (!strcmp(backend, "pipe"))
97 __dlog_init_pipe(config);
98 else if (!strcmp(backend, "logger"))
99 __dlog_init_android(config);
106 static void __set_plog_default_values()
108 for (size_t i = 0; i < NELEMS(plog); ++i)
109 plog_default_values[i] = plog[i];
112 static void __initialize_plog(const struct log_config *config)
116 const bool plog_default = log_config_get_boolean(config, "plog", DEFAULT_CONFIG_PLOG);
117 for (size_t i = 0; i < NELEMS(plog); ++i)
118 plog[i] = plog_default;
119 plog[LOG_ID_APPS] = true; // the default does not apply here for backward compatibility reasons.
120 __set_plog_default_values();
123 static void __configure_parameters(struct log_config *config)
127 __initialize_plog(config);
128 __update_plog(config);
129 __set_plog_default_values();
131 enable_secure_logs = log_config_get_boolean(config, "enable_secure_logs", enable_secure_logs);
132 debugmode = log_config_get_int(config, "debugmode", DEFAULT_CONFIG_DEBUGMODE);
133 fatal_assert = access(DEBUGMODE_FILE, F_OK) != -1;
134 limiter = log_config_get_boolean(config, "limiter", DEFAULT_CONFIG_LIMITER);
135 limiter_apply_to_all_buffers = log_config_get_int(config,
136 "limiter_apply_to_all_buffers",
137 DEFAULT_CONFIG_LIMITER_APPLY_TO_ALL_BUFFERS);
140 void __update_plog(const struct log_config *conf)
144 for (size_t i = 0; i < NELEMS(plog); ++i) {
145 char key[MAX_CONF_KEY_LEN];
146 const int r = snprintf(key, sizeof key, "enable_%s", log_name_by_id((log_id_t)i));
149 plog[i] = log_config_get_boolean(conf, key, plog_default_values[i]);
154 * @brief Configure the library
155 * @details Reads relevant config values
156 * @remarks This is more or less a constructor, but there are some obstacles
157 * to using it as such (i.e. with attribute constructor):
159 * - some important pieces of the system link to dlog, they start very early
160 * such that dlog can't properly initialize (which lasts for program lifetime)
161 * but don't actually log anything until later on and would be fine under lazy
162 * initialisation. The way to do it "properly" would be to expose this function
163 * into the API so that people can manually call it when they're ready, but
164 * one of the design goals of the current API is that it requires absolutely no
165 * other calls than `dlog_print`. Changing it would require somebody with a
166 * bird's eye view of the system to produce a design so I wouldn't count on it.
168 * - the constructor would need to have as high of a priority as possible (so as
169 * to minimize the risk of another library's constructor using uninitialized data)
170 * but at the same time others might want some room to wrap functions before
171 * dlog uses them (think mprobe/mcheck). This would also require a design pass.
176 bool __configure(void)
178 __attribute__((cleanup(log_config_free))) struct log_config config;
180 if (log_config_read(&config) < 0)
183 dynamic_config = __dynamic_config_create(&config);
185 __configure_parameters(&config);
187 if (!__configure_backend(&config)) {
188 __dynamic_config_destroy();
189 dynamic_config = false;
193 __configure_deduplicate(&config);
194 __configure_limiter(&config);
198 static void __attribute__((constructor(101))) __install_pipe_handler(void)
200 /* We mask SIGPIPE signal because most applications do not install their
201 * own SIGPIPE handler. Default behaviour in SIGPIPE case is to abort the
202 * process. SIGPIPE occurs when e.g. dlog daemon closes read pipe endpoint.
204 * We do this in the library constructor (at maximum priority) and not
205 * during regular (lazy) initialisation so as to prevent overwriting the
206 * program's actual signal handler, if it has one.
208 * In theory this is not required for the Android logger backend; however,
209 * this early we don't yet know the backend and also it is good to behave
210 * consistently in this regard anyway.
212 * We don't revert this in a destructor because Unix signals are bonkers
213 * and we have no way to do this cleanly. Most libdlog users don't use
214 * runtime linking so this would mostly done at program exit either way. */
215 signal(SIGPIPE, SIG_IGN);
218 static bool first = true;
219 static bool initialize()
224 /* The mutex acts as a barrier, but otherwise the C language's
225 * machine abstraction is single-threaded. This means that the
226 * compiler is free to rearrange calls inside the mutex according
227 * to the as-if rule because it doesn't care if another thread can
228 * access it in parallel. In particular, `is_initialized = true`
229 * directly after `__configure()` could be rearranged to go in
230 * front of it because it is not touched inside that function
231 * if the compiler thinks it helps somehow (not unlikely: since
232 * it is checked before the mutex, it is very probable for it to
233 * still be in the CPU register or something like that). On top
234 * of that, some architectures (in particular, armv7l) don't have
235 * strict memory guarantees and can reorder actual memory stores
236 * on their own, even if the compiler didn't do anything fancy
237 * when creating machine code. For more info about the issue,
238 * see https://www.aristeia.com/Papers/DDJ_Jul_Aug_2004_revised.pdf
240 * Ultimately this means that there needs to be some sort of
241 * barrier between `__configure` and `is_initialized = true`,
242 * and the simplest way to achieve that is to just wait until
243 * the second entry into the mutex. */
246 pthread_mutex_lock(&log_construction_lock);
248 first = !__configure();
250 is_initialized = true;
252 pthread_mutex_unlock(&log_construction_lock);
257 * @brief Fatal assertion
258 * @details Conditionally crash the sucka who sent the log
259 * @param[in] prio Priority of the log
261 static void __dlog_fatal_assert(int prio)
263 assert(!fatal_assert || (prio != DLOG_FATAL));
267 * @brief Check log validity
268 * @details Checks whether the log is valid and eligible for printing
269 * @param[in] log_id The target buffer ID
270 * @param[in] prio The log's priority
271 * @param[in] tag The log's tag
272 * @return DLOG_ERROR_NONE on success, else an error code.
273 * @retval DLOG_ERROR_INVALID_PARAMETER Invalid parameter
275 static int dlog_check_validity(log_id_t log_id, int prio, const char *tag)
279 return DLOG_ERROR_INVALID_PARAMETER;
281 if (log_id <= LOG_ID_INVALID || LOG_ID_MAX <= log_id)
282 return DLOG_ERROR_INVALID_PARAMETER;
284 return DLOG_ERROR_NONE;
288 * @brief Check log against limiter rules
289 * @details Checks whether the log passes current limiter rules
290 * @param[in] log_id The target buffer ID
291 * @param[in] prio The log's priority
292 * @param[in] tag The log's tag
293 * @return DLOG_ERROR_NONE on success, else an error code.
294 * @retval DLOG_ERROR_NOT_PERMITTED Not permitted
296 static int dlog_check_limiter(log_id_t log_id, int prio, const char *tag)
298 if (!debugmode && prio <= DLOG_DEBUG)
299 return DLOG_ERROR_NOT_PERMITTED;
302 __dynamic_config_update();
306 if (!pthread_rwlock_rdlock(&log_limiter_lock)) {
307 should_log = __log_limiter_pass_log(tag, prio);
308 pthread_rwlock_unlock(&log_limiter_lock);
312 return DLOG_ERROR_NOT_PERMITTED;
313 } else if (should_log < 0) {
315 int result = clock_gettime(CLOCK_MONOTONIC, &tp);
317 return DLOG_ERROR_NOT_PERMITTED;
318 write_to_log(log_id, prio, tag,
319 "Your log has been blocked due to limit of log lines per minute.", &tp);
320 return DLOG_ERROR_NOT_PERMITTED;
324 /* This can change due to __dynamic_config_update(), but is atomic and its
325 * value implies nothing else so does not need to be under a lock. */
327 return DLOG_ERROR_NOT_PERMITTED;
329 return DLOG_ERROR_NONE;
332 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)
334 if (check_should_log && prio < priority_filter_level)
335 return DLOG_ERROR_NONE;
337 if ((check_should_log || limiter_apply_to_all_buffers) && (dlog_check_limiter(log_id, prio, tag) < 0))
338 return DLOG_ERROR_NONE;
340 char buf[LOG_MAX_PAYLOAD_SIZE];
341 size_t len = vsnprintf(buf, sizeof buf, fmt, ap);
343 return DLOG_ERROR_NONE;
344 else if (len >= sizeof buf)
345 len = sizeof buf - 1;
348 int result = clock_gettime(CLOCK_MONOTONIC, &tp);
350 return DLOG_ERROR_NONE;
352 if (deduplicate(buf, len, &tp))
354 return write_to_log(log_id, prio, tag, buf, &tp);
357 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)
359 int ret = dlog_check_validity(log_id, prio, tag);
363 /* Threads can be cancelled before they give up a lock.
364 * Therefore cancellation is temporarily disabled.
365 * This solution is comparatively simple and cheap.
366 * The other solutions (cleanup handlers, robust mutexes)
367 * would be much more complicated and also inflict larger
368 * runtime costs. The downside of disabling cancellation
369 * is not a problem in our case because it is temporary
370 * and very brief so we don't keep an obsolete thread
371 * for much longer than we otherwise would. */
372 int old_cancel_state;
373 pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &old_cancel_state);
375 /* The only thing that needs to be protected here is `write_to_log` since
376 * all other resources already have their own specific locks (and even the
377 * pointer could be made to point at a null handler instead of a true NULL)
378 * but giving this guarantee makes everything a lot simpler as it removes
379 * the risk of something suddenly becoming NULL during processing. */
380 if (!initialize() || !write_to_log)
381 ret = DLOG_ERROR_NOT_PERMITTED;
382 else if (secure_log && !enable_secure_logs)
385 ret = __write_to_log_critical_section(log_id, prio, tag, fmt, ap, check_should_log);
387 pthread_setcancelstate(old_cancel_state, NULL);
392 int __critical_log_append_timestamp(char *buf, size_t buflen)
394 /* NB: the timestamp may slightly differ from the one that gets
395 * added onto the copy that goes into the regular buffer, and
396 * timestamp acquisition is duplicated. This would ideally be
397 * solved, but timestamps are currently added fairly deep in
398 * backend-specific functions so for now this will have to do.
399 * Also, since we're the sender, there is just this one set of
400 * timestamps, i.e. the send timestamp! The usual alternative
401 * set of receive timestamps will never have the opportunity
402 * to get added to the entry since this log is supposed to end
403 * up straight in the file (there's potentially the trusted
404 * writer binary but we're trying to keep the set of actions
405 * it needs to do to the minimum and those timestamps would
406 * in practice be the same anyway). */
409 clock_gettime(CLOCK_REALTIME, &ts);
410 const time_t tt = ts.tv_sec;
411 const long int real_millisec = ts.tv_nsec / 1000000;
412 clock_gettime(CLOCK_MONOTONIC, &ts);
414 struct tm *const ptm = localtime_r(&tt, &tmBuf);
415 assert(ptm); // we're in a short lived fork so asserts are fine and make things simple
417 int len = strftime(buf, buflen, "%m-%d %H:%M:%S", ptm);
420 int tmp_len = snprintf(buf + len, buflen - len, ".%03ld", real_millisec);
422 assert(tmp_len < buflen - len);
425 tmp_len = strftime(buf + len, buflen - len, "%z ", ptm);
426 assert(tmp_len != 0);
429 tmp_len = snprintf(buf + len, buflen - len, "%5lu.%03ld", ts.tv_sec, ts.tv_nsec / 1000000);
431 assert(tmp_len < buflen - len);
437 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)
439 int len = __critical_log_append_timestamp(buf, buflen);
440 const int metadata_len = snprintf(buf + len, buflen - len, " P%5d T%5d B%-6s %c/%-8s: ",
443 log_name_by_id(log_id),
444 filter_pri_to_char(prio),
445 tag ?: "CRITICAL_NO_TAG");
446 assert(metadata_len > 0);
447 if (metadata_len >= buflen - len)
448 return buflen - 1; // can genuinely happen with an exceedingly large tag
451 const int content_len = vsnprintf(buf + len, buflen - len, fmt, ap);
452 assert(content_len >= 0); // 0 is legit with format == ""
453 if (content_len >= buflen - len)
461 __attribute__ ((noreturn))
463 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)
465 char buf[LOG_MAX_PAYLOAD_SIZE + 128]; // extra space for some metadata
466 const int len = __critical_log_build_msg(buf, sizeof buf - 1, main_pid, main_tid, log_id, prio, tag, fmt, ap);
470 static const char *const path = "/usr/libexec/dlog-log-critical";
471 execl(path, path /* argv[0] convention */, buf, (char *) NULL);
474 /* Compilers are sometimes smart enough to recognize _exit's
475 * noreturn attribute, even if we wrap it with something that
476 * returns. This causes it to behave in unexpected ways, for
477 * example it can blow up the program regardless or it can
478 * optimize some conditionals out (and incorrectly enter them
479 * after the exit call fails to actually exit). This makes it
480 * unsuitable for tests. */
482 _exit(1); // not the regular `exit` so as not to trigger any `atexit` handlers prematurely
486 #ifndef UNIT_TEST // contains forks and exits, these don't work well with wrapping (see above)
487 void __critical_log(log_id_t log_id, int prio, const char *tag, const char *fmt, va_list ap)
489 /* Critical log functionality is mostly done in a separate binary
490 * to handle security correctly (else every process would have to
491 * possess the necessary privilege to write onto that file, which
492 * would be opening a fairly nasty can of worms from the security
493 * point of view). Our use of exec() is why a simple thread would
494 * not suffice and we're resorting to a fork.
496 * The double fork, much like a double barreled 12 gauge shotgun,
497 * is an elegant solution designed to stop a zombie army. We'd be
498 * creating zombie processes if we didn't wait() for the children
499 * we spawn, but we don't really want to do that since it results
500 * in a needless delay. Instead, the writer process is actually a
501 * grandchild, with our direct child exiting immediately just for
502 * us to have something to wait on that is guaranteed not to take
503 * too long. The orphaned grandchild is adopted by init, who will
504 * take care to reap it when it dies. In addition to avoiding the
505 * delay, the client will not have any unexpected children (which
506 * could ruin logic in its own waits).
509 * ┌───────┐ ┌─────────┐ ┌─────────────┐ ┌────────┐
510 * │ pid 1 ├──>│ libdlog ├──>│ immediately ├──>│ execs │
511 * │ init │ │ client │ │ exits │ │ writer │
512 * └───────┘ └─────────┘ └─────────────┘ └────────┘
514 * Afterwards, libdlog has no children:
515 * ┌───────┐ ┌─────────┐ ┌────────┐
516 * │ pid 1 ├──>│ libdlog │ ┌─────────>│ writer │
517 * │ init ├─┐ │ client │ │ │ binary │
518 * └───────┘ │ └─────────┘ │ └────────┘
519 * └──────────────────────┘
522 const pid_t main_pid = getpid();
523 const pid_t main_tid = gettid();
525 const int temporary_exiter_pid = fork();
526 if (temporary_exiter_pid < 0)
528 if (temporary_exiter_pid != 0) {
529 waitpid(temporary_exiter_pid, NULL, 0);
533 const int child_pid = fork();
539 __critical_log_child(main_pid, main_tid, log_id, prio, tag, fmt, ap);
542 int __dlog_critical_print(log_id_t log_id, int prio, const char *tag, const char *fmt, ...)
547 __critical_log(log_id, prio, tag, fmt, ap);
551 int ret = __dlog_vprint(log_id, prio, tag, fmt, ap);
558 int dlog_set_minimum_priority(int priority)
560 if (priority < DLOG_DEFAULT || priority > DLOG_PRIO_MAX)
561 return DLOG_ERROR_INVALID_PARAMETER;
563 priority_filter_level = priority;
564 return DLOG_ERROR_NONE;
569 * @details Print a log line
570 * @param[in] log_id The target buffer ID
571 * @param[in] prio Priority
573 * @param[in] fmt Format (same as printf)
574 * @param[in] ap Argument list
575 * @return Bytes written, or negative error
577 int __dlog_vprint(log_id_t log_id, int prio, const char *tag, const char *fmt, va_list ap)
579 int ret = __write_to_log(log_id, prio, tag, fmt, ap, true, false);
580 __dlog_fatal_assert(prio);
587 * @details Print a log line
588 * @param[in] log_id The target buffer ID
589 * @param[in] prio Priority
591 * @param[in] fmt Format (same as printf)
592 * @return Bytes written, or negative error
594 int __dlog_print(log_id_t log_id, int prio, const char *tag, const char *fmt, ...)
599 int ret = __dlog_vprint(log_id, prio, tag, fmt, ap);
607 * @details Print a log line
608 * @param[in] log_id The target buffer ID
609 * @param[in] prio Priority
611 * @param[in] fmt Format (same as printf)
612 * @return Bytes written, or negative error
614 int __dlog_sec_print(log_id_t log_id, int prio, const char *tag, const char *fmt, ...)
616 if (!enable_secure_logs)
622 int ret = __write_to_log(log_id, prio, tag, fmt, ap, true, true);
623 __dlog_fatal_assert(prio);
629 int dlog_vprint(log_priority prio, const char *tag, const char *fmt, va_list ap)
631 return __write_to_log(LOG_ID_APPS, prio, tag, fmt, ap, false, false);
634 int dlog_print(log_priority prio, const char *tag, const char *fmt, ...)
639 int ret = dlog_vprint(prio, tag, fmt, ap);
646 * @brief Finalize DLog
647 * @details Finalizes and deallocates the library
648 * @notes Used directly in tests; brings back the pre-init state
650 void __dlog_fini(void)
652 if (destroy_backend) {
654 destroy_backend = NULL;
657 is_initialized = false;
660 __deduplicate_destroy();
661 __log_limiter_destroy();
662 __dynamic_config_destroy();