liblog/log_is_loggable.c

/*
** Copyright 2014, The Android Open Source Project
**
** 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.
*/

#include <ctype.h>
#include <pthread.h>
#include <stdbool.h>
#include <stdlib.h>
#include <string.h>
#define _REALLY_INCLUDE_SYS__SYSTEM_PROPERTIES_H_
#include <sys/_system_properties.h>
#include <unistd.h>

#include <android/log.h>
#include <log/logger.h>
#include <private/android_logger.h>

#include "log_portability.h"

static pthread_mutex_t lock_loggable = PTHREAD_MUTEX_INITIALIZER;

static int lock()
{
    /*
     * If we trigger a signal handler in the middle of locked activity and the
     * signal handler logs a message, we could get into a deadlock state.
     */
    /*
     *  Any contention, and we can turn around and use the non-cached method
     * in less time than the system call associated with a mutex to deal with
     * the contention.
     */
    return pthread_mutex_trylock(&lock_loggable);
}

static void unlock()
{
    pthread_mutex_unlock(&lock_loggable);
}

struct cache {
    const prop_info* pinfo;
    uint32_t serial;
};

struct cache_char {
    struct cache cache;
    unsigned char c;
};

static int check_cache(struct cache* cache)
{
    return cache->pinfo
        && __system_property_serial(cache->pinfo) != cache->serial;
}

#define BOOLEAN_TRUE 0xFF
#define BOOLEAN_FALSE 0xFE

static void refresh_cache(struct cache_char* cache, const char* key)
{
    char buf[PROP_VALUE_MAX];

    if (!cache->cache.pinfo) {
        cache->cache.pinfo = __system_property_find(key);
        if (!cache->cache.pinfo) {
            return;
        }
    }
    cache->cache.serial = __system_property_serial(cache->cache.pinfo);
    __system_property_read(cache->cache.pinfo, 0, buf);
    switch(buf[0]) {
    case 't': case 'T':
        cache->c = strcasecmp(buf + 1, "rue") ? buf[0] : BOOLEAN_TRUE;
        break;
    case 'f': case 'F':
        cache->c = strcasecmp(buf + 1, "alse") ? buf[0] : BOOLEAN_FALSE;
        break;
    default:
        cache->c = buf[0];
    }
}

static int __android_log_level(const char* tag, size_t len, int default_prio)
{
    /* sizeof() is used on this array below */
    static const char log_namespace[] = "persist.log.tag.";
    static const size_t base_offset = 8; /* skip "persist." */
    /* calculate the size of our key temporary buffer */
    const size_t taglen = tag ? len : 0;
    /* sizeof(log_namespace) = strlen(log_namespace) + 1 */
    char key[sizeof(log_namespace) + taglen]; /* may be > PROP_NAME_MAX */
    char* kp;
    size_t i;
    char c = 0;
    /*
     * Single layer cache of four properties. Priorities are:
     *    log.tag.<tag>
     *    persist.log.tag.<tag>
     *    log.tag
     *    persist.log.tag
     * Where the missing tag matches all tags and becomes the
     * system global default. We do not support ro.log.tag* .
     */
    static char last_tag[PROP_NAME_MAX];
    static uint32_t global_serial;
    /* some compilers erroneously see uninitialized use. !not_locked */
    uint32_t current_global_serial = 0;
    static struct cache_char tag_cache[2];
    static struct cache_char global_cache[2];
    int change_detected;
    int global_change_detected;
    int not_locked;

    strcpy(key, log_namespace);

    global_change_detected = change_detected = not_locked = lock();

    if (!not_locked) {
        /*
         *  check all known serial numbers to changes.
         */
        for (i = 0; i < (sizeof(tag_cache) / sizeof(tag_cache[0])); ++i) {
            if (check_cache(&tag_cache[i].cache)) {
                change_detected = 1;
            }
        }
        for (i = 0; i < (sizeof(global_cache) / sizeof(global_cache[0])); ++i) {
            if (check_cache(&global_cache[i].cache)) {
                global_change_detected = 1;
            }
        }

        current_global_serial = __system_property_area_serial();
        if (current_global_serial != global_serial) {
            change_detected = 1;
            global_change_detected = 1;
        }
    }

    if (taglen) {
        int local_change_detected = change_detected;
        if (!not_locked) {
            if (!last_tag[0]
                    || (last_tag[0] != tag[0])
                    || strncmp(last_tag + 1, tag + 1,
                               (len < sizeof(last_tag)) ?
                                    (len - 1) :
                                    (sizeof(last_tag) - 1))
                    || ((len < sizeof(last_tag)) && last_tag[len])) {
                /* invalidate log.tag.<tag> cache */
                for (i = 0; i < (sizeof(tag_cache) / sizeof(tag_cache[0])); ++i) {
                    tag_cache[i].cache.pinfo = NULL;
                    tag_cache[i].c = '\0';
                }
                last_tag[0] = '\0';
                local_change_detected = 1;
            }
            if (!last_tag[0]) {
                if (len < sizeof(last_tag)) {
                    strncpy(last_tag, tag, len);
                    last_tag[len] = '\0';
                } else {
                    strncpy(last_tag, tag, sizeof(last_tag));
                }
            }
        }
        strncpy(key + sizeof(log_namespace) - 1, tag, len);
        key[sizeof(log_namespace) - 1 + len] = '\0';

        kp = key;
        for (i = 0; i < (sizeof(tag_cache) / sizeof(tag_cache[0])); ++i) {
            struct cache_char* cache = &tag_cache[i];
            struct cache_char temp_cache;

            if (not_locked) {
                temp_cache.cache.pinfo = NULL;
                temp_cache.c = '\0';
                cache = &temp_cache;
            }
            if (local_change_detected) {
                refresh_cache(cache, kp);
            }

            if (cache->c) {
                c = cache->c;
                break;
            }

            kp = key + base_offset;
        }
    }

    switch (toupper(c)) { /* if invalid, resort to global */
    case 'V':
    case 'D':
    case 'I':
    case 'W':
    case 'E':
    case 'F': /* Not officially supported */
    case 'A':
    case 'S':
    case BOOLEAN_FALSE: /* Not officially supported */
        break;
    default:
        /* clear '.' after log.tag */
        key[sizeof(log_namespace) - 2] = '\0';

        kp = key;
        for (i = 0; i < (sizeof(global_cache) / sizeof(global_cache[0])); ++i) {
            struct cache_char* cache = &global_cache[i];
            struct cache_char temp_cache;

            if (not_locked) {
                temp_cache = *cache;
                if (temp_cache.cache.pinfo != cache->cache.pinfo) { /* check atomic */
                    temp_cache.cache.pinfo = NULL;
                    temp_cache.c = '\0';
                }
                cache = &temp_cache;
            }
            if (global_change_detected) {
                refresh_cache(cache, kp);
            }

            if (cache->c) {
                c = cache->c;
                break;
            }

            kp = key + base_offset;
        }
        break;
    }

    if (!not_locked) {
        global_serial = current_global_serial;
        unlock();
    }

    switch (toupper(c)) {
    case 'V': return ANDROID_LOG_VERBOSE;
    case 'D': return ANDROID_LOG_DEBUG;
    case 'I': return ANDROID_LOG_INFO;
    case 'W': return ANDROID_LOG_WARN;
    case 'E': return ANDROID_LOG_ERROR;
    case 'F': /* FALLTHRU */ /* Not officially supported */
    case 'A': return ANDROID_LOG_FATAL;
    case BOOLEAN_FALSE: /* FALLTHRU */ /* Not Officially supported */
    case 'S': return -1; /* ANDROID_LOG_SUPPRESS */
    }
    return default_prio;
}

LIBLOG_ABI_PUBLIC int __android_log_is_loggable_len(int prio,
                                                    const char* tag, size_t len,
                                                    int default_prio)
{
    int logLevel = __android_log_level(tag, len, default_prio);
    return logLevel >= 0 && prio >= logLevel;
}

LIBLOG_ABI_PUBLIC int __android_log_is_loggable(int prio,
                                                const char* tag,
                                                int default_prio)
{
    int logLevel = __android_log_level(tag,
                                       (tag && *tag) ? strlen(tag) : 0,
                                       default_prio);
    return logLevel >= 0 && prio >= logLevel;
}

LIBLOG_ABI_PRIVATE int __android_log_is_debuggable()
{
    static uint32_t serial;
    static struct cache_char tag_cache;
    static const char key[] = "ro.debuggable";
    int ret;

    if (tag_cache.c) { /* ro property does not change after set */
        ret = tag_cache.c == '1';
    } else if (lock()) {
        struct cache_char temp_cache = { { NULL, -1 }, '\0' };
        refresh_cache(&temp_cache, key);
        ret = temp_cache.c == '1';
    } else {
        int change_detected = check_cache(&tag_cache.cache);
        uint32_t current_serial = __system_property_area_serial();
        if (current_serial != serial) {
            change_detected = 1;
        }
        if (change_detected) {
            refresh_cache(&tag_cache, key);
            serial = current_serial;
        }
        ret = tag_cache.c == '1';

        unlock();
    }

    return ret;
}

/*
 * For properties that are read often, but generally remain constant.
 * Since a change is rare, we will accept a trylock failure gracefully.
 * Use a separate lock from is_loggable to keep contention down b/25563384.
 */
struct cache2_char {
    pthread_mutex_t lock;
    uint32_t serial;
    const char* key_persist;
    struct cache_char cache_persist;
    const char* key_ro;
    struct cache_char cache_ro;
    unsigned char (*const evaluate)(const struct cache2_char *self);
};

static inline unsigned char do_cache2_char(struct cache2_char *self)
{
    uint32_t current_serial;
    int change_detected;
    unsigned char c;

    if (pthread_mutex_trylock(&self->lock)) {
        /* We are willing to accept some race in this context */
        return self->evaluate(self);
    }

    change_detected = check_cache(&self->cache_persist.cache)
                   || check_cache(&self->cache_ro.cache);
    current_serial = __system_property_area_serial();
    if (current_serial != self->serial) {
        change_detected = 1;
    }
    if (change_detected) {
        refresh_cache(&self->cache_persist, self->key_persist);
        refresh_cache(&self->cache_ro, self->key_ro);
        self->serial = current_serial;
    }
    c = self->evaluate(self);

    pthread_mutex_unlock(&self->lock);

    return c;
}

static unsigned char evaluate_persist_ro(const struct cache2_char *self)
{
    unsigned char c = self->cache_persist.c;

    if (c) {
        return c;
    }

    return self->cache_ro.c;
}

/*
 * Timestamp state generally remains constant, but can change at any time
 * to handle developer requirements.
 */
LIBLOG_ABI_PUBLIC clockid_t android_log_clockid()
{
    static struct cache2_char clockid = {
        PTHREAD_MUTEX_INITIALIZER,
        0,
        "persist.logd.timestamp",
        { { NULL, -1 }, '\0' },
        "ro.logd.timestamp",
        { { NULL, -1 }, '\0' },
        evaluate_persist_ro
    };

    return (tolower(do_cache2_char(&clockid)) == 'm')
        ? CLOCK_MONOTONIC
        : CLOCK_REALTIME;
}

/*
 * Security state generally remains constant, but the DO must be able
 * to turn off logging should it become spammy after an attack is detected.
 */
static unsigned char evaluate_security(const struct cache2_char *self)
{
    unsigned char c = self->cache_ro.c;

    return (c != BOOLEAN_FALSE) && c && (self->cache_persist.c == BOOLEAN_TRUE);
}

LIBLOG_ABI_PUBLIC int __android_log_security()
{
    static struct cache2_char security = {
        PTHREAD_MUTEX_INITIALIZER,
        0,
        "persist.logd.security",
        { { NULL, -1 }, BOOLEAN_FALSE },
        "ro.device_owner",
        { { NULL, -1 }, BOOLEAN_FALSE },
        evaluate_security
    };

    return do_cache2_char(&security);
}

/*
 * Interface that represents the logd buffer size determination so that others
 * need not guess our intentions.
 */

/* Property helper */
static bool check_flag(const char* prop, const char* flag) {
    const char* cp = strcasestr(prop, flag);
    if (!cp) {
        return false;
    }
    /* We only will document comma (,) */
    static const char sep[] = ",:;|+ \t\f";
    if ((cp != prop) && !strchr(sep, cp[-1])) {
        return false;
    }
    cp += strlen(flag);
    return !*cp || !!strchr(sep, *cp);
}

/* cache structure */
struct cache_property {
    struct cache cache;
    char property[PROP_VALUE_MAX];
};

static void refresh_cache_property(struct cache_property* cache, const char* key)
{
    if (!cache->cache.pinfo) {
        cache->cache.pinfo = __system_property_find(key);
        if (!cache->cache.pinfo) {
            return;
        }
    }
    cache->cache.serial = __system_property_serial(cache->cache.pinfo);
    __system_property_read(cache->cache.pinfo, 0, cache->property);
}

/* get boolean with the logger twist that supports eng adjustments */
LIBLOG_ABI_PRIVATE bool __android_logger_property_get_bool(const char* key,
                                                           int flag)
{
    struct cache_property property = { { NULL, -1 }, { 0 } };
    if (flag & BOOL_DEFAULT_FLAG_PERSIST) {
        char newkey[PROP_NAME_MAX];
        snprintf(newkey, sizeof(newkey), "ro.%s", key);
        refresh_cache_property(&property, newkey);
        property.cache.pinfo = NULL;
        property.cache.serial = -1;
        snprintf(newkey, sizeof(newkey), "persist.%s", key);
        refresh_cache_property(&property, newkey);
        property.cache.pinfo = NULL;
        property.cache.serial = -1;
    }

    refresh_cache_property(&property, key);

    if (check_flag(property.property, "true")) {
        return true;
    }
    if (check_flag(property.property, "false")) {
        return false;
    }
    if (check_flag(property.property, "eng")) {
       flag |= BOOL_DEFAULT_FLAG_ENG;
    }
    /* this is really a "not" flag */
    if (check_flag(property.property, "svelte")) {
       flag |= BOOL_DEFAULT_FLAG_SVELTE;
    }

    /* Sanity Check */
    if (flag & (BOOL_DEFAULT_FLAG_SVELTE | BOOL_DEFAULT_FLAG_ENG)) {
        flag &= ~BOOL_DEFAULT_FLAG_TRUE_FALSE;
        flag |= BOOL_DEFAULT_TRUE;
    }

    if ((flag & BOOL_DEFAULT_FLAG_SVELTE)
            && __android_logger_property_get_bool("ro.config.low_ram",
                                 BOOL_DEFAULT_FALSE)) {
        return false;
    }
    if ((flag & BOOL_DEFAULT_FLAG_ENG) && !__android_log_is_debuggable()) {
        return false;
    }

    return (flag & BOOL_DEFAULT_FLAG_TRUE_FALSE) != BOOL_DEFAULT_FALSE;
}

LIBLOG_ABI_PRIVATE bool __android_logger_valid_buffer_size(unsigned long value)
{
    static long pages, pagesize;
    unsigned long maximum;

    if ((value < LOG_BUFFER_MIN_SIZE) || (LOG_BUFFER_MAX_SIZE < value)) {
        return false;
    }

    if (!pages) {
        pages = sysconf(_SC_PHYS_PAGES);
    }
    if (pages < 1) {
        return true;
    }

    if (!pagesize) {
        pagesize = sysconf(_SC_PAGESIZE);
        if (pagesize <= 1) {
            pagesize = PAGE_SIZE;
        }
    }

    /* maximum memory impact a somewhat arbitrary ~3% */
    pages = (pages + 31) / 32;
    maximum = pages * pagesize;

    if ((maximum < LOG_BUFFER_MIN_SIZE) || (LOG_BUFFER_MAX_SIZE < maximum)) {
        return true;
    }

    return value <= maximum;
}

struct cache2_property_size {
    pthread_mutex_t lock;
    uint32_t serial;
    const char* key_persist;
    struct cache_property cache_persist;
    const char* key_ro;
    struct cache_property cache_ro;
    unsigned long (*const evaluate)(const struct cache2_property_size* self);
};

static inline unsigned long do_cache2_property_size(struct cache2_property_size* self)
{
    uint32_t current_serial;
    int change_detected;
    unsigned long v;

    if (pthread_mutex_trylock(&self->lock)) {
        /* We are willing to accept some race in this context */
        return self->evaluate(self);
    }

    change_detected = check_cache(&self->cache_persist.cache)
                   || check_cache(&self->cache_ro.cache);
    current_serial = __system_property_area_serial();
    if (current_serial != self->serial) {
        change_detected = 1;
    }
    if (change_detected) {
        refresh_cache_property(&self->cache_persist, self->key_persist);
        refresh_cache_property(&self->cache_ro, self->key_ro);
        self->serial = current_serial;
    }
    v = self->evaluate(self);

    pthread_mutex_unlock(&self->lock);

    return v;
}

static unsigned long property_get_size_from_cache(const struct cache_property* cache)
{
    char* cp;
    unsigned long value = strtoul(cache->property, &cp, 10);

    switch(*cp) {
    case 'm':
    case 'M':
        value *= 1024;
    /* FALLTHRU */
    case 'k':
    case 'K':
        value *= 1024;
    /* FALLTHRU */
    case '\0':
        break;

    default:
        value = 0;
    }

    if (!__android_logger_valid_buffer_size(value)) {
        value = 0;
    }

    return value;
}

static unsigned long evaluate_property_get_size(const struct cache2_property_size* self)
{
    unsigned long size = property_get_size_from_cache(&self->cache_persist);
    if (size) {
        return size;
    }
    return property_get_size_from_cache(&self->cache_ro);
}

LIBLOG_ABI_PRIVATE unsigned long __android_logger_get_buffer_size(log_id_t logId)
{
    static const char global_tunable[] = "persist.logd.size"; /* Settings App */
    static const char global_default[] = "ro.logd.size"; /* BoardConfig.mk */
    static struct cache2_property_size global = {
        PTHREAD_MUTEX_INITIALIZER,
        0,
        global_tunable,
        { { NULL, -1 }, {} },
        global_default,
        { { NULL, -1 }, {} },
        evaluate_property_get_size
    };
    char key_persist[PROP_NAME_MAX];
    char key_ro[PROP_NAME_MAX];
    struct cache2_property_size local = {
        PTHREAD_MUTEX_INITIALIZER,
        0,
        key_persist,
        { { NULL, -1 }, {} },
        key_ro,
        { { NULL, -1 }, {} },
        evaluate_property_get_size
    };
    unsigned long property_size, default_size;

    default_size =  do_cache2_property_size(&global);
    if (!default_size) {
        default_size = __android_logger_property_get_bool("ro.config.low_ram",
                                                          BOOL_DEFAULT_FALSE)
            ? LOG_BUFFER_MIN_SIZE /* 64K  */
            : LOG_BUFFER_SIZE;    /* 256K */
    }

    snprintf(key_persist, sizeof(key_persist), "%s.%s",
             global_tunable, android_log_id_to_name(logId));
    snprintf(key_ro, sizeof(key_ro), "%s.%s",
             global_default, android_log_id_to_name(logId));
    property_size = do_cache2_property_size(&local);

    if (!property_size) {
        property_size = default_size;
    }

    if (!property_size) {
        property_size = LOG_BUFFER_SIZE;
    }

    return property_size;
}