LeOS-GSI/LeOS/DnsResolver_hosts_cache.cpp

/*
 * Copyright (C) 2020 The LineageOS 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 <fcntl.h>
#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <strings.h>
#include <sys/file.h>
#include <sys/mman.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#include <utime.h>
#include <pthread.h>

#include <netinet/in6.h>
#include <arpa/inet.h>
#include <arpa/nameser.h>

#include "hostent.h"
#include "resolv_private.h"

constexpr int MAXALIASES = 35;
constexpr int MAXADDRS = 35;

#define MAX_ADDRLEN	(INET6_ADDRSTRLEN - (1 + 5))
#define MAX_HOSTLEN	MAXHOSTNAMELEN

#define ESTIMATED_LINELEN	32
#define HCFILE_ALLOC_SIZE	256

/* From sethostent.c */
#define ALIGNBYTES	(sizeof(uintptr_t) - 1)
#define ALIGN(p)	(((uintptr_t)(p) + ALIGNBYTES) &~ ALIGNBYTES)

/*
 * Host cache entry for hcfile.c_data.
 * Offsets are into hcfile.h_data.
 * Strings are *not* terminated by NULL, but by whitespace (isspace) or '#'.
 * Use hstr* functions with these.
 */
struct hcent
{
    uint32_t    addr;
    uint32_t    name;
};

/*
 * Overall host cache file state.
 */
struct hcfile
{
    int             h_fd;
    struct stat     h_st;
    char*           h_data;

    uint32_t        c_alloc;
    uint32_t        c_len;
    struct hcent*    c_data;
};
static struct hcfile hcfile;
static pthread_mutex_t hclock = PTHREAD_MUTEX_INITIALIZER;

static size_t hstrlen(const char *s)
{
    const char *p = s;
    while (*p && *p != '#' && !isspace(*p))
        ++p;
    return p - s;
}

static int hstrcmp(const char *a, const char *b)
{
    size_t alen = hstrlen(a);
    size_t blen = hstrlen(b);
    int res = strncmp(a, b, MIN(alen, blen));
    if (res == 0)
        res = alen - blen;
    return res;
}

static char *hstrcpy(char *dest, const char *src)
{
    size_t len = hstrlen(src);
    memcpy(dest, src, len);
    dest[len] = '\0';
    return dest;
}

static char *hstrdup(const char *s)
{
    size_t len = hstrlen(s);
    char *dest = (char *)malloc(len + 1);
    if (!dest)
        return NULL;
    memcpy(dest, s, len);
    dest[len] = '\0';
    return dest;
}

static int cmp_hcent_name(const void *a, const void *b)
{
    struct hcent *ea = (struct hcent *)a;
    const char *na = hcfile.h_data + ea->name;
    struct hcent *eb = (struct hcent *)b;
    const char *nb = hcfile.h_data + eb->name;

    return hstrcmp(na, nb);
}

static struct hcent *_hcfindname(const char *name)
{
    size_t first, last, mid;
    struct hcent *cur = NULL;
    int cmp;

    if (hcfile.c_len == 0)
        return NULL;

    first = 0;
    last = hcfile.c_len - 1;
    mid = (first + last) / 2;
    while (first <= last) {
        cur = hcfile.c_data + mid;
        cmp = hstrcmp(hcfile.h_data + cur->name, name);
        if (cmp == 0)
            goto found;
        if (cmp < 0)
            first = mid + 1;
        else {
            if (mid > 0)
                last = mid - 1;
            else
                return NULL;
        }
        mid = (first + last) / 2;
    }
    return NULL;

found:
    while (cur > hcfile.c_data) {
        struct hcent *prev = cur - 1;
        cmp = cmp_hcent_name(cur, prev);
        if (cmp)
            break;
        cur = prev;
    }

    return cur;
}

/*
 * Find next name on line, if any.
 *
 * Assumes that line is terminated by LF.
 */
static const char *_hcnextname(const char *name)
{
    while (!isspace(*name)) {
        if (*name == '#')
            return NULL;
        ++name;
    }
    while (isspace(*name)) {
        if (*name == '\n')
            return NULL;
        ++name;
    }
    if (*name == '#')
        return NULL;
    return name;
}

static int _hcfilemmap(void)
{
    struct stat st;
    int h_fd;
    char *h_addr;
    const char *p, *pend;
    uint32_t c_alloc;

    h_fd = open(_PATH_HOSTS, O_CLOEXEC);
    if (h_fd < 0)
        return -1;
    if (flock(h_fd, LOCK_EX) != 0) {
        close(h_fd);
        return -1;
    }

    if (hcfile.h_data) {
        memset(&st, 0, sizeof(st));
        if (fstat(h_fd, &st) == 0) {
            if (st.st_size == hcfile.h_st.st_size &&
                st.st_mtime == hcfile.h_st.st_mtime) {
                flock(h_fd, LOCK_UN);
                close(h_fd);
                return 0;
            }
        }
        free(hcfile.c_data);
        munmap(hcfile.h_data, hcfile.h_st.st_size);
        close(hcfile.h_fd);
        memset(&hcfile, 0, sizeof(struct hcfile));
    }

    if (fstat(h_fd, &st) != 0) {
        flock(h_fd, LOCK_UN);
        close(h_fd);
        return -1;
    }
    h_addr = (char*)mmap(NULL, st.st_size, PROT_READ, MAP_SHARED, h_fd, 0);
    if (h_addr == MAP_FAILED) {
        flock(h_fd, LOCK_UN);
        close(h_fd);
        return -1;
    }

    hcfile.h_fd = h_fd;
    hcfile.h_st = st;
    hcfile.h_data = h_addr;

    c_alloc = 0;
    /*
     * Do an initial allocation if the file is "large".  Estimate
     * 32 bytes per line and define "large" as more than half of
     * the alloc growth size (256 entries).
     */
    if (st.st_size >= ESTIMATED_LINELEN * HCFILE_ALLOC_SIZE / 2) {
        c_alloc = st.st_size / ESTIMATED_LINELEN;
        hcfile.c_data = (struct hcent*)malloc(c_alloc * sizeof(struct hcent));
        if (!hcfile.c_data) {
            goto oom;
        }
    }

    p = (const char *)h_addr;
    pend = p + st.st_size;
    while (p < pend) {
        const char *eol, *addr, *name;
        size_t len;
        addr = p;
        eol = (const char*)memchr(p, '\n', pend - p);
        if (!eol)
            break;
        p = eol + 1;
        if (*addr == '#' || *addr == '\n')
            continue;
        len = hstrlen(addr);
        if (len > MAX_ADDRLEN)
            continue;
        name = addr + len;
        while (name < eol && isspace(*name))
            ++name;
        while (name < eol) {
            len = hstrlen(name);
            if (len == 0)
                break;
            if (len < MAX_HOSTLEN) {
                struct hcent *ent;
                if (c_alloc <= hcfile.c_len) {
                    struct hcent *c_data;
                    c_alloc += HCFILE_ALLOC_SIZE;
                    c_data = (struct hcent*)realloc(hcfile.c_data, c_alloc * sizeof(struct hcent));
                    if (!c_data) {
                        goto oom;
                    }
                    hcfile.c_data = c_data;
                }
                ent = hcfile.c_data + hcfile.c_len;
                ent->addr = addr - h_addr;
                ent->name = name - h_addr;
                ++hcfile.c_len;
            }
            name += len;
            while (name < eol && isspace(*name))
                ++name;
        }
    }

    qsort(hcfile.c_data, hcfile.c_len,
        sizeof(struct hcent), cmp_hcent_name);

    flock(h_fd, LOCK_UN);

    return 0;

oom:
    free(hcfile.c_data);
    munmap(hcfile.h_data, hcfile.h_st.st_size);
    flock(hcfile.h_fd, LOCK_UN);
    close(hcfile.h_fd);
    memset(&hcfile, 0, sizeof(struct hcfile));
    return -1;
}

/*
 * Caching version of getaddrinfo.
 *
 * If we find the requested host name in the cache, use getaddrinfo to
 * populate the result for each address we find.
 *
 * Note glibc and bionic differ in the handling of ai_canonname.  POSIX
 * says that ai_canonname is only populated in the first result entry.
 * glibc does this.  bionic populates ai_canonname in all result entries.
 * We choose the POSIX/glibc way here.
 */
int hc_getaddrinfo(const char *name, const struct addrinfo* hints, struct addrinfo** result)
{
    int ret = 0;
    struct hcent *ent, *cur;
    struct addrinfo *ai;
    struct addrinfo rhints;
    struct addrinfo *last;
    int canonname = 0;
    int cmp;

    if (getenv("ANDROID_HOSTS_CACHE_DISABLE") != NULL)
        return EAI_SYSTEM;

    if (!name)
        return EAI_SYSTEM;

    pthread_mutex_lock(&hclock);

    if (_hcfilemmap() != 0) {
        ret = EAI_SYSTEM;
        goto out;
    }
    ent = _hcfindname(name);
    if (!ent) {
        ret = EAI_NONAME;
        goto out;
    }

    if (hints) {
        canonname = (hints->ai_flags & AI_CANONNAME);
        memcpy(&rhints, hints, sizeof(rhints));
        rhints.ai_flags &= ~AI_CANONNAME;
    }
    else {
        memset(&rhints, 0, sizeof(rhints));
    }
    rhints.ai_flags |= AI_NUMERICHOST;

    last = NULL;
    cur = ent;
    do {
        char addrstr[MAX_ADDRLEN];
        struct addrinfo *res;

        hstrcpy(addrstr, hcfile.h_data + cur->addr);

        if (getaddrinfo_numeric(addrstr, nullptr, rhints, &res) == 0) {
            if (!last)
                (*result)->ai_next = res;
            else
                last->ai_next = res;
            last = res;
            while (last->ai_next)
                last = last->ai_next;
        }

        if(cur + 1 >= hcfile.c_data + hcfile.c_len)
            break;
        cmp = cmp_hcent_name(cur, cur + 1);
        cur = cur + 1;
    }
    while (!cmp);

    if (last == NULL) {
        /* This check is equivalent to (*result)->ai_next == NULL */
        ret = EAI_NODATA;
        goto out;
    }

    if (canonname) {
        ai = (*result)->ai_next;
        free(ai->ai_canonname);
        ai->ai_canonname = hstrdup(hcfile.h_data + ent->name);
    }

out:
    pthread_mutex_unlock(&hclock);
    return ret;
}

/*
 * Caching version of gethtbyname.
 *
 * Note glibc and bionic differ in the handling of aliases.  glibc returns
 * all aliases for all entries, regardless of whether they match h_addrtype.
 * bionic returns only the aliases for the first hosts entry.  We return all
 * aliases for all IPv4 entries.
 *
 * Additionally, if an alias is IPv6 and the primary name for an alias also
 * has an IPv4 entry, glibc will return the IPv4 address(es), but bionic
 * will not.  Neither do we.
 */
int hc_gethtbyname(const char *host, int af, struct getnamaddr *info)
{
    int ret = NETDB_SUCCESS;
    struct hcent *ent, *cur;
    int cmp;
    size_t addrlen;
    unsigned int naliases = 0;
    char *aliases[MAXALIASES];
    unsigned int naddrs = 0;
    char *addr_ptrs[MAXADDRS];
    unsigned int n;

    if (getenv("ANDROID_HOSTS_CACHE_DISABLE") != NULL)
        return NETDB_INTERNAL;

    switch (af) {
    case AF_INET:  addrlen = NS_INADDRSZ;  break;
    case AF_INET6: addrlen = NS_IN6ADDRSZ; break;
    default:
        return NETDB_INTERNAL;
    }

    pthread_mutex_lock(&hclock);

    if (_hcfilemmap() != 0) {
        ret = NETDB_INTERNAL;
        goto out;
    }

    ent = _hcfindname(host);
    if (!ent) {
        ret = HOST_NOT_FOUND;
        goto out;
    }

    cur = ent;
	do {
		char addr[16];
		char addrstr[MAX_ADDRLEN];
		char namestr[MAX_HOSTLEN];
		const char *name;

		hstrcpy(addrstr, hcfile.h_data + cur->addr);
		if (inet_pton(af, addrstr, &addr) == 1) {
/* 			char *aligned;
			First match is considered the official hostname */
			if (naddrs == 0) {
				hstrcpy(namestr, hcfile.h_data + cur->name);
				HENT_SCOPY(info->hp->h_name, namestr, info->buf, info->buflen);
			}
			for (name = hcfile.h_data + cur->name; name; name = _hcnextname(name)) {
				if (!hstrcmp(name, host))
					continue;
				hstrcpy(namestr, name);
				HENT_SCOPY(aliases[naliases], namestr, info->buf, info->buflen);
				++naliases;
				if (naliases >= MAXALIASES)
					goto nospc;
			}
/* 			aligned = (char *)ALIGN(info->buf);
			if (info->buf != aligned) {
				if ((ptrdiff_t)info->buflen < (aligned - info->buf))
					goto nospc;
				info->buflen -= (aligned - info->buf);
				info->buf = aligned;
			} */
			HENT_COPY(addr_ptrs[naddrs], addr, addrlen, info->buf, info->buflen);
			++naddrs;
			if (naddrs >= MAXADDRS)
				goto nospc;
		}

        if(cur + 1 >= hcfile.c_data + hcfile.c_len)
            break;
        cmp = cmp_hcent_name(cur, cur + 1);
        cur = cur + 1;
    }
    while (!cmp);

    if (naddrs == 0) {
        ret = HOST_NOT_FOUND;
        goto out;
    }

    addr_ptrs[naddrs++] = NULL;
    aliases[naliases++] = NULL;

    /* hp->h_name already populated */
    HENT_ARRAY(info->hp->h_aliases, naliases, info->buf, info->buflen);
    for (n = 0; n < naliases; ++n) {
        info->hp->h_aliases[n] = aliases[n];
    }
    info->hp->h_addrtype = af;
    info->hp->h_length = addrlen;
    HENT_ARRAY(info->hp->h_addr_list, naddrs, info->buf, info->buflen);
    for (n = 0; n < naddrs; ++n) {
        info->hp->h_addr_list[n] = addr_ptrs[n];
    }

out:
    pthread_mutex_unlock(&hclock);
    return ret;

nospc:
    ret = NETDB_INTERNAL;
    goto out;
}