Systemd/src/resolve/resolved-etc-hosts.c

468 lines
16 KiB
C

/* SPDX-License-Identifier: LGPL-2.1-or-later */
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#include "fd-util.h"
#include "fileio.h"
#include "hostname-util.h"
#include "resolved-dns-synthesize.h"
#include "resolved-etc-hosts.h"
#include "socket-netlink.h"
#include "stat-util.h"
#include "string-util.h"
#include "strv.h"
#include "time-util.h"
/* Recheck /etc/hosts at most once every 2s */
#define ETC_HOSTS_RECHECK_USEC (2*USEC_PER_SEC)
static void etc_hosts_item_free(EtcHostsItem *item) {
strv_free(item->names);
free(item);
}
static void etc_hosts_item_by_name_free(EtcHostsItemByName *item) {
free(item->name);
free(item->addresses);
free(item);
}
void etc_hosts_free(EtcHosts *hosts) {
hosts->by_address = hashmap_free_with_destructor(hosts->by_address, etc_hosts_item_free);
hosts->by_name = hashmap_free_with_destructor(hosts->by_name, etc_hosts_item_by_name_free);
hosts->no_address = set_free_free(hosts->no_address);
}
void manager_etc_hosts_flush(Manager *m) {
etc_hosts_free(&m->etc_hosts);
m->etc_hosts_stat = (struct stat) {};
}
static int parse_line(EtcHosts *hosts, unsigned nr, const char *line) {
_cleanup_free_ char *address_str = NULL;
struct in_addr_data address = {};
bool found = false;
EtcHostsItem *item;
int r;
assert(hosts);
assert(line);
r = extract_first_word(&line, &address_str, NULL, EXTRACT_RELAX);
if (r < 0)
return log_error_errno(r, "/etc/hosts:%u: failed to extract address: %m", nr);
assert(r > 0); /* We already checked that the line is not empty, so it should contain *something* */
r = in_addr_ifindex_from_string_auto(address_str, &address.family, &address.address, NULL);
if (r < 0) {
log_warning_errno(r, "/etc/hosts:%u: address '%s' is invalid, ignoring: %m", nr, address_str);
return 0;
}
r = in_addr_is_null(address.family, &address.address);
if (r < 0) {
log_warning_errno(r, "/etc/hosts:%u: address '%s' is invalid, ignoring: %m", nr, address_str);
return 0;
}
if (r > 0)
/* This is an 0.0.0.0 or :: item, which we assume means that we shall map the specified hostname to
* nothing. */
item = NULL;
else {
/* If this is a normal address, then simply add entry mapping it to the specified names */
item = hashmap_get(hosts->by_address, &address);
if (!item) {
r = hashmap_ensure_allocated(&hosts->by_address, &in_addr_data_hash_ops);
if (r < 0)
return log_oom();
item = new(EtcHostsItem, 1);
if (!item)
return log_oom();
*item = (EtcHostsItem) {
.address = address,
};
r = hashmap_put(hosts->by_address, &item->address, item);
if (r < 0) {
free(item);
return log_oom();
}
}
}
for (;;) {
_cleanup_free_ char *name = NULL;
EtcHostsItemByName *bn;
r = extract_first_word(&line, &name, NULL, EXTRACT_RELAX);
if (r < 0)
return log_error_errno(r, "/etc/hosts:%u: couldn't extract hostname: %m", nr);
if (r == 0)
break;
found = true;
r = dns_name_is_valid_ldh(name);
if (r <= 0) {
log_warning_errno(r, "/etc/hosts:%u: hostname \"%s\" is not valid, ignoring.", nr, name);
continue;
}
if (!item) {
/* Optimize the case where we don't need to store any addresses, by storing
* only the name in a dedicated Set instead of the hashmap */
r = set_ensure_consume(&hosts->no_address, &dns_name_hash_ops, TAKE_PTR(name));
if (r < 0)
return r;
continue;
}
r = strv_extend(&item->names, name);
if (r < 0)
return log_oom();
bn = hashmap_get(hosts->by_name, name);
if (!bn) {
r = hashmap_ensure_allocated(&hosts->by_name, &dns_name_hash_ops);
if (r < 0)
return log_oom();
bn = new0(EtcHostsItemByName, 1);
if (!bn)
return log_oom();
r = hashmap_put(hosts->by_name, name, bn);
if (r < 0) {
free(bn);
return log_oom();
}
bn->name = TAKE_PTR(name);
}
if (!GREEDY_REALLOC(bn->addresses, bn->n_allocated, bn->n_addresses + 1))
return log_oom();
bn->addresses[bn->n_addresses++] = &item->address;
}
if (!found)
log_warning("/etc/hosts:%u: line is missing any hostnames", nr);
return 0;
}
static void strip_localhost(EtcHosts *hosts) {
static const struct in_addr_data local_in_addrs[] = {
{
.family = AF_INET,
#if __BYTE_ORDER == __LITTLE_ENDIAN
/* We want constant expressions here, that's why we don't use htole32() here */
.address.in.s_addr = UINT32_C(0x0100007F),
#else
.address.in.s_addr = UINT32_C(0x7F000001),
#endif
},
{
.family = AF_INET6,
.address.in6 = IN6ADDR_LOOPBACK_INIT,
},
};
EtcHostsItem *item;
assert(hosts);
/* Removes the 'localhost' entry from what we loaded. But only if the mapping is exclusively between
* 127.0.0.1 and localhost (or aliases to that we recognize). If there's any other name assigned to
* it, we leave the entry in.
*
* This way our regular synthesizing can take over, but only if it would result in the exact same
* mappings. */
for (size_t j = 0; j < ELEMENTSOF(local_in_addrs); j++) {
bool all_localhost, in_order;
char **i;
item = hashmap_get(hosts->by_address, local_in_addrs + j);
if (!item)
continue;
/* Check whether all hostnames the loopback address points to are localhost ones */
all_localhost = true;
STRV_FOREACH(i, item->names)
if (!is_localhost(*i)) {
all_localhost = false;
break;
}
if (!all_localhost) /* Not all names are localhost, hence keep the entries for this address. */
continue;
/* Now check if the names listed for this address actually all point back just to this
* address (or the other loopback address). If not, let's stay away from this too. */
in_order = true;
STRV_FOREACH(i, item->names) {
EtcHostsItemByName *n;
bool all_local_address;
n = hashmap_get(hosts->by_name, *i);
if (!n) /* No reverse entry? Then almost certainly the entry already got deleted from
* the previous iteration of this loop, i.e. via the other protocol */
break;
/* Now check if the addresses of this item are all localhost addresses */
all_local_address = true;
for (size_t m = 0; m < n->n_addresses; m++)
if (!in_addr_is_localhost(n->addresses[m]->family, &n->addresses[m]->address)) {
all_local_address = false;
break;
}
if (!all_local_address) {
in_order = false;
break;
}
}
if (!in_order)
continue;
STRV_FOREACH(i, item->names) {
EtcHostsItemByName *n;
n = hashmap_remove(hosts->by_name, *i);
if (n)
etc_hosts_item_by_name_free(n);
}
assert_se(hashmap_remove(hosts->by_address, local_in_addrs + j) == item);
etc_hosts_item_free(item);
}
}
int etc_hosts_parse(EtcHosts *hosts, FILE *f) {
_cleanup_(etc_hosts_free) EtcHosts t = {};
unsigned nr = 0;
int r;
for (;;) {
_cleanup_free_ char *line = NULL;
char *l;
r = read_line(f, LONG_LINE_MAX, &line);
if (r < 0)
return log_error_errno(r, "Failed to read /etc/hosts: %m");
if (r == 0)
break;
nr++;
l = strchr(line, '#');
if (l)
*l = '\0';
l = strstrip(line);
if (isempty(l))
continue;
r = parse_line(&t, nr, l);
if (r < 0)
return r;
}
strip_localhost(&t);
etc_hosts_free(hosts);
*hosts = t;
t = (EtcHosts) {}; /* prevent cleanup */
return 0;
}
static int manager_etc_hosts_read(Manager *m) {
_cleanup_fclose_ FILE *f = NULL;
struct stat st;
usec_t ts;
int r;
assert_se(sd_event_now(m->event, clock_boottime_or_monotonic(), &ts) >= 0);
/* See if we checked /etc/hosts recently already */
if (m->etc_hosts_last != USEC_INFINITY && m->etc_hosts_last + ETC_HOSTS_RECHECK_USEC > ts)
return 0;
m->etc_hosts_last = ts;
if (m->etc_hosts_stat.st_mode != 0) {
if (stat("/etc/hosts", &st) < 0) {
if (errno != ENOENT)
return log_error_errno(errno, "Failed to stat /etc/hosts: %m");
manager_etc_hosts_flush(m);
return 0;
}
/* Did the mtime or ino/dev change? If not, there's no point in re-reading the file. */
if (stat_inode_unmodified(&m->etc_hosts_stat, &st))
return 0;
}
f = fopen("/etc/hosts", "re");
if (!f) {
if (errno != ENOENT)
return log_error_errno(errno, "Failed to open /etc/hosts: %m");
manager_etc_hosts_flush(m);
return 0;
}
/* Take the timestamp at the beginning of processing, so that any changes made later are read on the next
* invocation */
r = fstat(fileno(f), &st);
if (r < 0)
return log_error_errno(errno, "Failed to fstat() /etc/hosts: %m");
r = etc_hosts_parse(&m->etc_hosts, f);
if (r < 0)
return r;
m->etc_hosts_stat = st;
m->etc_hosts_last = ts;
return 1;
}
int manager_etc_hosts_lookup(Manager *m, DnsQuestion* q, DnsAnswer **answer) {
bool found_a = false, found_aaaa = false;
struct in_addr_data k = {};
EtcHostsItemByName *bn;
DnsResourceKey *t;
const char *name;
unsigned i;
int r;
assert(m);
assert(q);
assert(answer);
if (!m->read_etc_hosts)
return 0;
(void) manager_etc_hosts_read(m);
name = dns_question_first_name(q);
if (!name)
return 0;
r = dns_name_address(name, &k.family, &k.address);
if (r > 0) {
EtcHostsItem *item;
DnsResourceKey *found_ptr = NULL;
item = hashmap_get(m->etc_hosts.by_address, &k);
if (!item)
return 0;
/* We have an address in /etc/hosts that matches the queried name. Let's return successful. Actual data
* we'll only return if the request was for PTR. */
DNS_QUESTION_FOREACH(t, q) {
if (!IN_SET(t->type, DNS_TYPE_PTR, DNS_TYPE_ANY))
continue;
if (!IN_SET(t->class, DNS_CLASS_IN, DNS_CLASS_ANY))
continue;
r = dns_name_equal(dns_resource_key_name(t), name);
if (r < 0)
return r;
if (r > 0) {
found_ptr = t;
break;
}
}
if (found_ptr) {
char **n;
r = dns_answer_reserve(answer, strv_length(item->names));
if (r < 0)
return r;
STRV_FOREACH(n, item->names) {
_cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
rr = dns_resource_record_new(found_ptr);
if (!rr)
return -ENOMEM;
rr->ptr.name = strdup(*n);
if (!rr->ptr.name)
return -ENOMEM;
r = dns_answer_add(*answer, rr, 0, DNS_ANSWER_AUTHENTICATED);
if (r < 0)
return r;
}
}
return 1;
}
bn = hashmap_get(m->etc_hosts.by_name, name);
if (bn) {
r = dns_answer_reserve(answer, bn->n_addresses);
if (r < 0)
return r;
} else {
/* Check if name was listed with no address. If yes, continue to return an answer. */
if (!set_contains(m->etc_hosts.no_address, name))
return 0;
}
DNS_QUESTION_FOREACH(t, q) {
if (!IN_SET(t->type, DNS_TYPE_A, DNS_TYPE_AAAA, DNS_TYPE_ANY))
continue;
if (!IN_SET(t->class, DNS_CLASS_IN, DNS_CLASS_ANY))
continue;
r = dns_name_equal(dns_resource_key_name(t), name);
if (r < 0)
return r;
if (r == 0)
continue;
if (IN_SET(t->type, DNS_TYPE_A, DNS_TYPE_ANY))
found_a = true;
if (IN_SET(t->type, DNS_TYPE_AAAA, DNS_TYPE_ANY))
found_aaaa = true;
if (found_a && found_aaaa)
break;
}
for (i = 0; bn && i < bn->n_addresses; i++) {
_cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
if ((!found_a && bn->addresses[i]->family == AF_INET) ||
(!found_aaaa && bn->addresses[i]->family == AF_INET6))
continue;
r = dns_resource_record_new_address(&rr, bn->addresses[i]->family, &bn->addresses[i]->address, bn->name);
if (r < 0)
return r;
r = dns_answer_add(*answer, rr, 0, DNS_ANSWER_AUTHENTICATED);
if (r < 0)
return r;
}
return found_a || found_aaaa;
}