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Systemd/src/resolve/resolved-etc-hosts.c
Zbigniew Jędrzejewski-Szmek be19cdf31c resolved: change error handling for manager_etc_hosts_read() 
The choice what errors to ignore is left to the caller, and the caller is
changed to ignore all errors.

On error, previously read data is kept. So if e.g. an oom error happens, we
will continue to return slightly stale data instead of pretending we have no
entries for the given address. I think that's better, for example when
/etc/hosts contains some important overrides that external DNS should not be
queried for.
2018-08-01 12:45:54 +02:00

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/* SPDX-License-Identifier: LGPL-2.1+ */
#include "fd-util.h"
#include "fileio.h"
#include "hostname-util.h"
#include "resolved-etc-hosts.h"
#include "resolved-dns-synthesize.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 inline void etc_hosts_item_free(EtcHostsItem *item) {
strv_free(item->names);
free(item);
}
static inline 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_mtime = USEC_INFINITY;
}
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, "Couldn't extract address, in line /etc/hosts:%u.", nr);
if (r == 0) {
log_error("Premature end of line, in line /etc/hosts:%u.", nr);
return -EINVAL;
}
r = in_addr_ifindex_from_string_auto(address_str, &address.family, &address.address, NULL);
if (r < 0)
return log_error_errno(r, "Address '%s' is invalid, in line /etc/hosts:%u.", address_str, nr);
r = in_addr_is_null(address.family, &address.address);
if (r < 0)
return r;
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 = new0(EtcHostsItem, 1);
if (!item)
return log_oom();
item->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, "Couldn't extract host name, in line /etc/hosts:%u.", nr);
if (r == 0)
break;
r = dns_name_is_valid(name);
if (r <= 0)
return log_error_errno(r, "Hostname %s is not valid, ignoring, in line /etc/hosts:%u.", name, nr);
found = true;
if (is_localhost(name))
/* Suppress the "localhost" line that is often seen */
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_allocated(&hosts->no_address, &dns_name_hash_ops);
if (r < 0)
return log_oom();
r = set_put(hosts->no_address, name);
if (r < 0)
return r;
TAKE_PTR(name);
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_error("Line is missing any host names, in line /etc/hosts:%u.", nr);
return -EINVAL;
}
return 0;
}
int etc_hosts_parse(EtcHosts *hosts, FILE *f) {
_cleanup_(etc_hosts_free) EtcHosts t = {};
char line[LINE_MAX];
unsigned nr = 0;
int r;
FOREACH_LINE(line, f, return log_error_errno(errno, "Failed to read /etc/hosts: %m")) {
char *l;
nr++;
l = strstrip(line);
if (isempty(l))
continue;
if (l[0] == '#')
continue;
r = parse_line(&t, nr, l);
if (r < 0)
return r;
}
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_mtime != USEC_INFINITY) {
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 change? If not, there's no point in re-reading the file. */
if (timespec_load(&st.st_mtim) == m->etc_hosts_mtime)
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_mtime = timespec_load(&st.st_mtim);
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;
}
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