Don't wait until lazy init to block SIGPIPE

[platform/core/system/dlog.git] / src / libdlog / log.c

/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: t -*-
 * DLOG
 * Copyright (c) 2005-2008, The Android Open Source Project
 * Copyright (c) 2012-2013 Samsung Electronics Co., Ltd.
 *
 * Licensed under the Apache License, Version 2.0 (the License);
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

// C
#include <assert.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>

// POSIX
#include <pthread.h>
#include <sys/wait.h>
#include <unistd.h>

// DLog
#include <dynamic_config.h>
#include <libdlog.h>
#include <logcommon.h>
#include "logconfig.h"
#include "loglimiter.h"

#define DEFAULT_CONFIG_LIMITER false
#define DEFAULT_CONFIG_PLOG true
#define DEFAULT_CONFIG_DEBUGMODE 0
#define DEFAULT_CONFIG_LIMITER_APPLY_TO_ALL_BUFFERS 0

/**
 * @brief Points to a function which writes a log message
 * @details The function pointed to depends on the backend used
 * @param[in] log_id ID of the buffer to log to. Belongs to (LOG_ID_INVALID, LOG_ID_MAX) non-inclusive
 * @param[in] prio Priority of the message.
 * @param[in] tag The message tag, identifies the sender.
 * @param[in] msg The contents of the message.
 * @return Returns the number of bytes written on success and a negative error value on error.
 * @see __dlog_init_backend
 */
int (*write_to_log)(log_id_t log_id, log_priority prio, const char *tag, const char *msg) = NULL;
void (*destroy_backend)();

pthread_rwlock_t log_limiter_lock = PTHREAD_RWLOCK_INITIALIZER;
static pthread_mutex_t log_construction_lock = PTHREAD_MUTEX_INITIALIZER;
static bool is_initialized = false;

extern void __dlog_init_pipe(const struct log_config *conf);
extern void __dlog_init_android(const struct log_config *conf);

bool limiter;
static bool dynamic_config;
static bool plog[LOG_ID_MAX];
static bool plog_default_values[LOG_ID_MAX];

static int debugmode;
static int fatal_assert;
static int limiter_apply_to_all_buffers;

static void __configure_limiter(struct log_config *config)
{
        assert(config);

        if (!limiter)
                return;

        limiter = __log_limiter_create(config);
}

static int __configure_backend(struct log_config *config)
{
        assert(config);

        const char *const backend = log_config_get(config, "backend");
        if (!backend)
                return 0;

        if (!strcmp(backend, "pipe"))
                __dlog_init_pipe(config);
        else if (!strcmp(backend, "logger"))
                __dlog_init_android(config);
        else
                return 0;

        return 1;
}

static void __set_plog_default_values()
{
        for (int i = 0; i < NELEMS(plog); ++i)
                plog_default_values[i] = plog[i];
}

static void __initialize_plog(const struct log_config *config)
{
        assert(config);

        const bool plog_default = log_config_get_boolean(config, "plog", DEFAULT_CONFIG_PLOG);
        for (int i = 0; i < NELEMS(plog); ++i)
                plog[i] = plog_default;
        plog[LOG_ID_APPS] = true; // the default does not apply here for backward compatibility reasons.
        __set_plog_default_values();
}

static void __configure_parameters(struct log_config *config)
{
        assert(config);

        __initialize_plog(config);
        __update_plog(config);
        __set_plog_default_values();

        debugmode = log_config_get_int(config, "debugmode", DEFAULT_CONFIG_DEBUGMODE);
        fatal_assert = access(DEBUGMODE_FILE, F_OK) != -1;
        limiter = log_config_get_boolean(config, "limiter", DEFAULT_CONFIG_LIMITER);
        limiter_apply_to_all_buffers = log_config_get_int(config,
                                                                        "limiter_apply_to_all_buffers",
                                                                        DEFAULT_CONFIG_LIMITER_APPLY_TO_ALL_BUFFERS);
}

void __update_plog(const struct log_config *conf)
{
        assert(conf);

        for (int i = 0; i < NELEMS(plog); ++i) {
                char key[MAX_CONF_KEY_LEN];
                const int r = snprintf(key, sizeof key, "enable_%s", log_name_by_id((log_id_t)i));
                if (r < 0)
                        continue;
                plog[i] = log_config_get_boolean(conf, key, plog_default_values[i]);
        }
}

/**
 * @brief Configure the library
 * @details Reads relevant config values
 * @remarks This is more or less a constructor, but there are some obstacles
 *          to using it as such (i.e. with attribute constructor):
 *
 *  - some important pieces of the system link to dlog, they start very early
 *    such that dlog can't properly initialize (which lasts for program lifetime)
 *    but don't actually log anything until later on and would be fine under lazy
 *    initialisation. The way to do it "properly" would be to expose this function
 *    into the API so that people can manually call it when they're ready, but
 *    one of the design goals of the current API is that it requires absolutely no
 *    other calls than `dlog_print`. Changing it would require somebody with a
 *    bird's eye view of the system to produce a design so I wouldn't count on it.
 *
 *  - the constructor would need to have as high of a priority as possible (so as
 *    to minimize the risk of another library's constructor using uninitialized data)
 *    but at the same time others might want some room to wrap functions before
 *    dlog uses them (think mprobe/mcheck). This would also require a design pass.
 */
#ifndef UNIT_TEST
static
#endif
bool __configure(void)
{
        __attribute__((cleanup(log_config_free))) struct log_config config;

        if (log_config_read(&config) < 0)
                return false;

        dynamic_config = __dynamic_config_create(&config);

        __configure_parameters(&config);

        if (!__configure_backend(&config)) {
                __dynamic_config_destroy();
                dynamic_config = false;
                return false;
        }

        __configure_limiter(&config);
        return true;
}

static void __attribute__((constructor(101))) __install_pipe_handler(void)
{
        /* We mask SIGPIPE signal because most applications do not install their
         * own SIGPIPE handler. Default behaviour in SIGPIPE case is to abort the
         * process. SIGPIPE occurs when e.g. dlog daemon closes read pipe endpoint.
         *
         * We do this in the library constructor (at maximum priority) and not
         * during regular (lazy) initialisation so as to prevent overwriting the
         * program's actual signal handler, if it has one.
         *
         * In theory this is not required for the Android logger backend; however,
         * this early we don't yet know the backend and also it is good to behave
         * consistently in this regard anyway.
         *
         * We don't revert this in a destructor because Unix signals are bonkers
         * and we have no way to do this cleanly. Most libdlog users don't use
         * runtime linking so this would mostly done at program exit either way. */
        signal(SIGPIPE, SIG_IGN);
}

static bool first = true;
static bool initialize()
{
        if (is_initialized)
                return true;

        /* The mutex acts as a barrier, but otherwise the C language's
         * machine abstraction is single-threaded. This means that the
         * compiler is free to rearrange calls inside the mutex according
         * to the as-if rule because it doesn't care if another thread can
         * access it in parallel. In particular, `is_initialized = true`
         * directly after `__configure()` could be rearranged to go in
         * front of it because it is not touched inside that function
         * if the compiler thinks it helps somehow (not unlikely: since
         * it is checked before the mutex, it is very probable for it to
         * still be in the CPU register or something like that). On top
         * of that, some architectures (in particular, armv7l) don't have
         * strict memory guarantees and can reorder actual memory stores
         * on their own, even if the compiler didn't do anything fancy
         * when creating machine code. For more info about the issue,
         * see https://www.aristeia.com/Papers/DDJ_Jul_Aug_2004_revised.pdf
         *
         * Ultimately this means that there needs to be some sort of
         * barrier between `__configure` and `is_initialized = true`,
         * and the simplest way to achieve that is to just wait until
         * the second entry into the mutex. */

        bool ret;
        pthread_mutex_lock(&log_construction_lock);
                if (first)
                        first = !__configure();
                else
                        is_initialized = true;
                ret = !first;
        pthread_mutex_unlock(&log_construction_lock);
        return ret;
}

/**
 * @brief Fatal assertion
 * @details Conditionally crash the sucka who sent the log
 * @param[in] prio Priority of the log
 */
static void __dlog_fatal_assert(int prio)
{
        assert(!fatal_assert || (prio != DLOG_FATAL));
}

/**
 * @brief Check log validity
 * @details Checks whether the log is valid and eligible for printing
 * @param[in] log_id The target buffer ID
 * @param[in] prio The log's priority
 * @param[in] tag The log's tag
 * @return DLOG_ERROR_NONE on success, else an error code.
 * @retval DLOG_ERROR_INVALID_PARAMETER Invalid parameter
 */
static int dlog_check_validity(log_id_t log_id, int prio, const char *tag)
{
        if (!tag)
                return DLOG_ERROR_INVALID_PARAMETER;

        if (log_id <= LOG_ID_INVALID || LOG_ID_MAX <= log_id)
                return DLOG_ERROR_INVALID_PARAMETER;

        return DLOG_ERROR_NONE;
}

/**
 * @brief Check log against limiter rules
 * @details Checks whether the log passes current limiter rules
 * @param[in] log_id The target buffer ID
 * @param[in] prio The log's priority
 * @param[in] tag The log's tag
 * @return DLOG_ERROR_NONE on success, else an error code.
 * @retval DLOG_ERROR_NOT_PERMITTED Not permitted
 */
static int dlog_check_limiter(log_id_t log_id, int prio, const char *tag)
{
        if (!debugmode && prio <= DLOG_DEBUG)
                return DLOG_ERROR_NOT_PERMITTED;

        if (dynamic_config)
                __dynamic_config_update();

        if (limiter) {
                int should_log = 0;
                if (!pthread_rwlock_rdlock(&log_limiter_lock)) {
                        should_log = __log_limiter_pass_log(tag, prio);
                        pthread_rwlock_unlock(&log_limiter_lock);
                }

                if (!should_log) {
                        return DLOG_ERROR_NOT_PERMITTED;
                } else if (should_log < 0) {
                        write_to_log(log_id, prio, tag,
                                        "Your log has been blocked due to limit of log lines per minute.");
                        return DLOG_ERROR_NOT_PERMITTED;
                }
        }

        /* This can change due to __dynamic_config_update(), but is atomic and its
         * value implies nothing else so does not need to be under a lock. */
        if (!plog[log_id])
                return DLOG_ERROR_NOT_PERMITTED;

        return DLOG_ERROR_NONE;
}

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)
{
        if ((check_should_log || limiter_apply_to_all_buffers) && (dlog_check_limiter(log_id, prio, tag) < 0))
                return DLOG_ERROR_NONE;

        char buf[LOG_MAX_PAYLOAD_SIZE];
        vsnprintf(buf, sizeof buf, fmt, ap);
        return write_to_log(log_id, prio, tag, buf);
}

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)
{
        int ret = dlog_check_validity(log_id, prio, tag);
        if (ret < 0)
                return ret;

        /* Threads can be cancelled before they give up a lock.
         * Therefore cancellation is temporarily disabled.
         * This solution is comparatively simple and cheap.
         * The other solutions (cleanup handlers, robust mutexes)
         * would be much more complicated and also inflict larger
         * runtime costs. The downside of disabling cancellation
         * is not a problem in our case because it is temporary
         * and very brief so we don't keep an obsolete thread
         * for much longer than we otherwise would. */
        int old_cancel_state;
        pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &old_cancel_state);

        /* The only thing that needs to be protected here is `write_to_log` since
         * all other resources already have their own specific locks (and even the
         * pointer could be made to point at a null handler instead of a true NULL)
         * but giving this guarantee makes everything a lot simpler as it removes
         * the risk of something suddenly becoming NULL during processing. */
        ret = !initialize() || !write_to_log
                ? DLOG_ERROR_NOT_PERMITTED
                : __write_to_log_critical_section(log_id, prio, tag, fmt, ap, check_should_log)
                ;

        pthread_setcancelstate(old_cancel_state, NULL);

        return ret;
}

int __critical_log_append_timestamp(char *buf, size_t buflen)
{
        /* NB: the timestamp may slightly differ from the one that gets
         * added onto the copy that goes into the regular buffer, and
         * timestamp acquisition is duplicated. This would ideally be
         * solved, but timestamps are currently added fairly deep in
         * backend-specific functions so for now this will have to do.
         * Also, since we're the sender, there is just this one set of
         * timestamps, i.e. the send timestamp! The usual alternative
         * set of receive timestamps will never have the opportunity
         * to get added to the entry since this log is supposed to end
         * up straight in the file (there's potentially the trusted
         * writer binary but we're trying to keep the set of actions
         * it needs to do to the minimum and those timestamps would
         * in practice be the same anyway). */

        struct timespec ts;
        clock_gettime(CLOCK_REALTIME, &ts);
        const time_t tt = ts.tv_sec;
        const long int real_millisec = ts.tv_nsec / 1000000;
        clock_gettime(CLOCK_MONOTONIC, &ts);
#ifdef HAVE_LOCALTIME_R
        struct tm tmBuf;
        struct tm *const ptm = localtime_r(&tt, &tmBuf);
#else
        struct tm *const ptm = localtime(&tt);
#endif
        assert(ptm); // we're in a short lived fork so asserts are fine and make things simple

        int len = strftime(buf, buflen, "%m-%d %H:%M:%S", ptm);
        assert(len != 0);

        int tmp_len = snprintf(buf + len, buflen - len, ".%03ld", real_millisec);
        assert(tmp_len > 0);
        assert(tmp_len < buflen - len);
        len += tmp_len;

        tmp_len = strftime(buf + len, buflen - len, "%z ", ptm);
        assert(tmp_len != 0);
        len += tmp_len;

        tmp_len = snprintf(buf + len, buflen - len, "%5lu.%03ld", ts.tv_sec, ts.tv_nsec / 1000000);
        assert(tmp_len > 0);
        assert(tmp_len < buflen - len);
        len += tmp_len;

        return len;
}

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)
{
        int len = __critical_log_append_timestamp(buf, buflen);
        const int metadata_len = snprintf(buf + len, buflen - len, " P%5d T%5d B%-6s %c/%-8s: ",
                main_pid,
                main_tid,
                log_name_by_id(log_id),
                filter_pri_to_char(prio),
                tag ?: "CRITICAL_NO_TAG");
        assert(metadata_len > 0);
        if (metadata_len >= buflen - len)
                return buflen - 1; // can genuinely happen with an exceedingly large tag
        len += metadata_len;

        const int content_len = vsnprintf(buf + len, buflen - len, fmt, ap);
        assert(content_len >= 0); // 0 is legit with format == ""
        if (content_len >= buflen - len)
                return buflen - 1;
        len += content_len;

        return len;
}

#ifndef UNIT_TEST
__attribute__ ((noreturn))
#endif
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)
{
        char buf[LOG_MAX_PAYLOAD_SIZE + 128]; // extra space for some metadata
        const int len = __critical_log_build_msg(buf, sizeof buf - 1, main_pid, main_tid, log_id, prio, tag, fmt, ap);
        buf[len] = '\n';
        buf[len + 1] = '\0';

        static const char *const path = "/usr/libexec/dlog-log-critical";
        execl(path, path /* argv[0] convention */, buf, (char *) NULL);

#ifndef UNIT_TEST
        /* Compilers are sometimes smart enough to recognize _exit's
         * noreturn attribute, even if we wrap it with something that
         * returns. This causes it to behave in unexpected ways, for
         * example it can blow up the program regardless or it can
         * optimize some conditionals out (and incorrectly enter them
         * after the exit call fails to actually exit). This makes it
         * unsuitable for tests. */

        _exit(1); // not the regular `exit` so as not to trigger any `atexit` handlers prematurely
#endif
}

#ifndef UNIT_TEST // contains forks and exits, these don't work well with wrapping (see above)
void __critical_log(log_id_t log_id, int prio, const char *tag, const char *fmt, va_list ap)
{
        /* Critical log functionality is mostly done in a separate binary
         * to handle security correctly (else every process would have to
         * possess the necessary privilege to write onto that file, which
         * would be opening a fairly nasty can of worms from the security
         * point of view). Our use of exec() is why a simple thread would
         * not suffice and we're resorting to a fork.
         *
         * The double fork, much like a double barreled 12 gauge shotgun,
         * is an elegant solution designed to stop a zombie army. We'd be
         * creating zombie processes if we didn't wait() for the children
         * we spawn, but we don't really want to do that since it results
         * in a needless delay. Instead, the writer process is actually a
         * grandchild, with our direct child exiting immediately just for
         * us to have something to wait on that is guaranteed not to take
         * too long. The orphaned grandchild is adopted by init, who will
         * take care to reap it when it dies. In addition to avoiding the
         * delay, the client will not have any unexpected children (which
         * could ruin logic in its own waits).
         *
         * Right after forks:
         * ┌───────┐   ┌─────────┐   ┌─────────────┐   ┌────────┐
         * │ pid 1 ├──>│ libdlog ├──>│ immediately ├──>│ execs  │
         * │ init  │   │ client  │   │    exits    │   │ writer │
         * └───────┘   └─────────┘   └─────────────┘   └────────┘
         *
         * Afterwards, libdlog has no children:
         * ┌───────┐   ┌─────────┐                     ┌────────┐
         * │ pid 1 ├──>│ libdlog │          ┌─────────>│ writer │
         * │ init  ├─┐ │ client  │          │          │ binary │
         * └───────┘ │ └─────────┘          │          └────────┘
         *           └──────────────────────┘
         */

        const pid_t main_pid = getpid();
        const pid_t main_tid = gettid();

        const int temporary_exiter_pid = fork();
        if (temporary_exiter_pid < 0)
                return;
        if (temporary_exiter_pid != 0) {
                waitpid(temporary_exiter_pid, NULL, 0);
                return;
        }

        const int child_pid = fork();
        if (child_pid < 0)
                _exit(1);
        if (child_pid != 0)
                _exit(0);

        __critical_log_child(main_pid, main_tid, log_id, prio, tag, fmt, ap);
}

int __dlog_critical_print(log_id_t log_id, int prio, const char *tag, const char *fmt, ...)
{
        va_list ap;

        va_start(ap, fmt);
        __critical_log(log_id, prio, tag, fmt, ap);
        va_end(ap);

        va_start(ap, fmt);
        int ret = __dlog_vprint(log_id, prio, tag, fmt, ap);
        va_end(ap);

        return ret;
}
#endif

/**
 * @brief Print log
 * @details Print a log line
 * @param[in] log_id The target buffer ID
 * @param[in] prio Priority
 * @param[in] tag tag
 * @param[in] fmt Format (same as printf)
 * @param[in] ap Argument list
 * @return Bytes written, or negative error
 */
int __dlog_vprint(log_id_t log_id, int prio, const char *tag, const char *fmt, va_list ap)
{
        int ret = __write_to_log(log_id, prio, tag, fmt, ap, true);
        __dlog_fatal_assert(prio);

        return ret;
}

/**
 * @brief Print log
 * @details Print a log line
 * @param[in] log_id The target buffer ID
 * @param[in] prio Priority
 * @param[in] tag tag
 * @param[in] fmt Format (same as printf)
 * @return Bytes written, or negative error
 */
int __dlog_print(log_id_t log_id, int prio, const char *tag, const char *fmt, ...)
{
        va_list ap;

        va_start(ap, fmt);
        int ret = __dlog_vprint(log_id, prio, tag, fmt, ap);
        va_end(ap);

        return ret;
}

/**
 * @brief Print log
 * @details Print a log line
 * @param[in] log_id The target buffer ID
 * @param[in] prio Priority
 * @param[in] tag tag
 * @param[in] fmt Format (same as printf)
 * @return Bytes written, or negative error
 */
int __dlog_sec_print(log_id_t log_id, int prio, const char *tag, const char *fmt, ...)
{
        va_list ap;

        va_start(ap, fmt);
        int ret = __dlog_vprint(log_id, prio, tag, fmt, ap);
        va_end(ap);

        return ret;
}

int dlog_vprint(log_priority prio, const char *tag, const char *fmt, va_list ap)
{
        return __write_to_log(LOG_ID_APPS, prio, tag, fmt, ap, false);
}

int dlog_print(log_priority prio, const char *tag, const char *fmt, ...)
{
        va_list ap;

        va_start(ap, fmt);
        int ret = dlog_vprint(prio, tag, fmt, ap);
        va_end(ap);

        return ret;
}

/**
 * @brief Finalize DLog
 * @details Finalizes and deallocates the library
 * @notes Used directly in tests; brings back the pre-init state
 */
void __dlog_fini(void)
{
        if (destroy_backend) {
                destroy_backend();
                destroy_backend = NULL;
        }
        write_to_log = NULL;
        is_initialized = false;
        first = true;

        __log_limiter_destroy();
        __dynamic_config_destroy();
}