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Systemd/src/resolve/resolved-resolv-conf.c
Lennart Poettering 0d53667334 tree-wide: use __fsetlocking() instead of fxyz_unlocked() 
Let's replace usage of fputc_unlocked() and friends by __fsetlocking(f,
FSETLOCKING_BYCALLER). This turns off locking for the entire FILE*,
instead of doing individual per-call decision whether to use normal
calls or _unlocked() calls.

This has various benefits:

1. It's easier to read and easier not to forget

2. It's more comprehensive, as fprintf() and friends are covered too
   (as these functions have no _unlocked() counterpart)

3. Philosophically, it's a bit more correct, because it's more a
   property of the file handle really whether we ever pass it on to another
   thread, not of the operations we then apply to it.

This patch reworks all pieces of codes that so far used fxyz_unlocked()
calls to use __fsetlocking() instead. It also reworks all places that
use open_memstream(), i.e. use stdio FILE* for string manipulations.

Note that this in some way a revert of 4b61c87511.
2017-12-14 10:42:25 +01:00

364 lines
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/* SPDX-License-Identifier: LGPL-2.1+ */
/***
This file is part of systemd.
Copyright 2014 Tom Gundersen <teg@jklm.no>
systemd is free software; you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or
(at your option) any later version.
systemd is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with systemd; If not, see <http://www.gnu.org/licenses/>.
***/
#include <resolv.h>
#include <stdio_ext.h>
#include "alloc-util.h"
#include "dns-domain.h"
#include "fd-util.h"
#include "fileio-label.h"
#include "fileio.h"
#include "ordered-set.h"
#include "resolved-conf.h"
#include "resolved-dns-server.h"
#include "resolved-resolv-conf.h"
#include "string-util.h"
#include "strv.h"
/* A resolv.conf file containing the DNS server and domain data we learnt from uplink, i.e. the full uplink data */
#define PRIVATE_UPLINK_RESOLV_CONF "/run/systemd/resolve/resolv.conf"
/* A resolv.conf file containing the domain data we learnt from uplink, but our own DNS server address. */
#define PRIVATE_STUB_RESOLV_CONF "/run/systemd/resolve/stub-resolv.conf"
/* A static resolv.conf file containing no domains, but only our own DNS sever address */
#define PRIVATE_STATIC_RESOLV_CONF ROOTLIBEXECDIR "/resolv.conf"
static bool file_is_our_own(const struct stat *st) {
const char *path;
assert(st);
FOREACH_STRING(path,
PRIVATE_UPLINK_RESOLV_CONF,
PRIVATE_STUB_RESOLV_CONF,
PRIVATE_STATIC_RESOLV_CONF) {
struct stat own;
/* Is it symlinked to our own uplink file? */
if (stat(path, &own) >= 0 &&
st->st_dev == own.st_dev &&
st->st_ino == own.st_ino)
return true;
}
return false;
}
int manager_read_resolv_conf(Manager *m) {
_cleanup_fclose_ FILE *f = NULL;
struct stat st;
char line[LINE_MAX];
int r;
assert(m);
/* Reads the system /etc/resolv.conf, if it exists and is not
* symlinked to our own resolv.conf instance */
if (!m->read_resolv_conf)
return 0;
r = stat("/etc/resolv.conf", &st);
if (r < 0) {
if (errno == ENOENT)
return 0;
r = log_warning_errno(errno, "Failed to stat /etc/resolv.conf: %m");
goto clear;
}
/* Have we already seen the file? */
if (timespec_load(&st.st_mtim) == m->resolv_conf_mtime)
return 0;
if (file_is_our_own(&st))
return 0;
f = fopen("/etc/resolv.conf", "re");
if (!f) {
if (errno == ENOENT)
return 0;
r = log_warning_errno(errno, "Failed to open /etc/resolv.conf: %m");
goto clear;
}
if (fstat(fileno(f), &st) < 0) {
r = log_error_errno(errno, "Failed to stat open file: %m");
goto clear;
}
if (file_is_our_own(&st))
return 0;
dns_server_mark_all(m->dns_servers);
dns_search_domain_mark_all(m->search_domains);
FOREACH_LINE(line, f, r = -errno; goto clear) {
const char *a;
char *l;
l = strstrip(line);
if (IN_SET(*l, '#', ';'))
continue;
a = first_word(l, "nameserver");
if (a) {
r = manager_parse_dns_server_string_and_warn(m, DNS_SERVER_SYSTEM, a);
if (r < 0)
log_warning_errno(r, "Failed to parse DNS server address '%s', ignoring.", a);
continue;
}
a = first_word(l, "domain");
if (!a) /* We treat "domain" lines, and "search" lines as equivalent, and add both to our list. */
a = first_word(l, "search");
if (a) {
r = manager_parse_search_domains_and_warn(m, a);
if (r < 0)
log_warning_errno(r, "Failed to parse search domain string '%s', ignoring.", a);
}
}
m->resolv_conf_mtime = timespec_load(&st.st_mtim);
/* Flush out all servers and search domains that are still
* marked. Those are then ones that didn't appear in the new
* /etc/resolv.conf */
dns_server_unlink_marked(m->dns_servers);
dns_search_domain_unlink_marked(m->search_domains);
/* Whenever /etc/resolv.conf changes, start using the first
* DNS server of it. This is useful to deal with broken
* network managing implementations (like NetworkManager),
* that when connecting to a VPN place both the VPN DNS
* servers and the local ones in /etc/resolv.conf. Without
* resetting the DNS server to use back to the first entry we
* will continue to use the local one thus being unable to
* resolve VPN domains. */
manager_set_dns_server(m, m->dns_servers);
/* Unconditionally flush the cache when /etc/resolv.conf is
* modified, even if the data it contained was completely
* identical to the previous version we used. We do this
* because altering /etc/resolv.conf is typically done when
* the network configuration changes, and that should be
* enough to flush the global unicast DNS cache. */
if (m->unicast_scope)
dns_cache_flush(&m->unicast_scope->cache);
/* If /etc/resolv.conf changed, make sure to forget everything we learned about the DNS servers. After all we
* might now talk to a very different DNS server that just happens to have the same IP address as an old one
* (think 192.168.1.1). */
dns_server_reset_features_all(m->dns_servers);
return 0;
clear:
dns_server_unlink_all(m->dns_servers);
dns_search_domain_unlink_all(m->search_domains);
return r;
}
static void write_resolv_conf_server(DnsServer *s, FILE *f, unsigned *count) {
assert(s);
assert(f);
assert(count);
if (!dns_server_string(s)) {
log_warning("Our of memory, or invalid DNS address. Ignoring server.");
return;
}
/* Check if the DNS server is limited to particular domains;
* resolv.conf does not have a syntax to express that, so it must not
* appear as a global name server to avoid routing unrelated domains to
* it (which is a privacy violation, will most probably fail anyway,
* and adds unnecessary load) */
if (dns_server_limited_domains(s)) {
log_debug("DNS server %s has route-only domains, not using as global name server", dns_server_string(s));
return;
}
if (*count == MAXNS)
fputs("# Too many DNS servers configured, the following entries may be ignored.\n", f);
(*count)++;
fprintf(f, "nameserver %s\n", dns_server_string(s));
}
static void write_resolv_conf_search(
OrderedSet *domains,
FILE *f) {
unsigned length = 0, count = 0;
Iterator i;
char *domain;
assert(domains);
assert(f);
fputs("search", f);
ORDERED_SET_FOREACH(domain, domains, i) {
if (++count > MAXDNSRCH) {
fputs("\n# Too many search domains configured, remaining ones ignored.", f);
break;
}
length += strlen(domain) + 1;
if (length > 256) {
fputs("\n# Total length of all search domains is too long, remaining ones ignored.", f);
break;
}
fputc(' ', f);
fputs(domain, f);
}
fputs("\n", f);
}
static int write_uplink_resolv_conf_contents(FILE *f, OrderedSet *dns, OrderedSet *domains) {
Iterator i;
fputs("# This file is managed by man:systemd-resolved(8). Do not edit.\n"
"#\n"
"# This is a dynamic resolv.conf file for connecting local clients directly to\n"
"# all known uplink DNS servers. This file lists all configured search domains.\n"
"#\n"
"# Third party programs must not access this file directly, but only through the\n"
"# symlink at /etc/resolv.conf. To manage man:resolv.conf(5) in a different way,\n"
"# replace this symlink by a static file or a different symlink.\n"
"#\n"
"# See man:systemd-resolved.service(8) for details about the supported modes of\n"
"# operation for /etc/resolv.conf.\n"
"\n", f);
if (ordered_set_isempty(dns))
fputs("# No DNS servers known.\n", f);
else {
unsigned count = 0;
DnsServer *s;
ORDERED_SET_FOREACH(s, dns, i)
write_resolv_conf_server(s, f, &count);
}
if (!ordered_set_isempty(domains))
write_resolv_conf_search(domains, f);
return fflush_and_check(f);
}
static int write_stub_resolv_conf_contents(FILE *f, OrderedSet *dns, OrderedSet *domains) {
fputs_unlocked("# This file is managed by man:systemd-resolved(8). Do not edit.\n"
"#\n"
"# This is a dynamic resolv.conf file for connecting local clients to the\n"
"# internal DNS stub resolver of systemd-resolved. This file lists all\n"
"# configured search domains.\n"
"#\n"
"# Run \"systemd-resolve --status\" to see details about the uplink DNS servers\n"
"# currently in use.\n"
"#\n"
"# Third party programs must not access this file directly, but only through the\n"
"# symlink at /etc/resolv.conf. To manage man:resolv.conf(5) in a different way,\n"
"# replace this symlink by a static file or a different symlink.\n"
"#\n"
"# See man:systemd-resolved.service(8) for details about the supported modes of\n"
"# operation for /etc/resolv.conf.\n"
"\n"
"nameserver 127.0.0.53\n", f);
if (!ordered_set_isempty(domains))
write_resolv_conf_search(domains, f);
return fflush_and_check(f);
}
int manager_write_resolv_conf(Manager *m) {
_cleanup_ordered_set_free_ OrderedSet *dns = NULL, *domains = NULL;
_cleanup_free_ char *temp_path_uplink = NULL, *temp_path_stub = NULL;
_cleanup_fclose_ FILE *f_uplink = NULL, *f_stub = NULL;
int r;
assert(m);
/* Read the system /etc/resolv.conf first */
(void) manager_read_resolv_conf(m);
/* Add the full list to a set, to filter out duplicates */
r = manager_compile_dns_servers(m, &dns);
if (r < 0)
return log_warning_errno(r, "Failed to compile list of DNS servers: %m");
r = manager_compile_search_domains(m, &domains, false);
if (r < 0)
return log_warning_errno(r, "Failed to compile list of search domains: %m");
r = fopen_temporary_label(PRIVATE_UPLINK_RESOLV_CONF, PRIVATE_UPLINK_RESOLV_CONF, &f_uplink, &temp_path_uplink);
if (r < 0)
return log_warning_errno(r, "Failed to open private resolv.conf file for writing: %m");
(void) __fsetlocking(f_uplink, FSETLOCKING_BYCALLER);
(void) fchmod(fileno(f_uplink), 0644);
r = fopen_temporary_label(PRIVATE_STUB_RESOLV_CONF, PRIVATE_STUB_RESOLV_CONF, &f_stub, &temp_path_stub);
if (r < 0)
return log_warning_errno(r, "Failed to open private stub-resolv.conf file for writing: %m");
(void) __fsetlocking(f_stub, FSETLOCKING_BYCALLER);
(void) fchmod(fileno(f_stub), 0644);
r = write_uplink_resolv_conf_contents(f_uplink, dns, domains);
if (r < 0) {
log_error_errno(r, "Failed to write private resolv.conf contents: %m");
goto fail;
}
if (rename(temp_path_uplink, PRIVATE_UPLINK_RESOLV_CONF) < 0) {
r = log_error_errno(errno, "Failed to move private resolv.conf file into place: %m");
goto fail;
}
r = write_stub_resolv_conf_contents(f_stub, dns, domains);
if (r < 0) {
log_error_errno(r, "Failed to write private stub-resolv.conf contents: %m");
goto fail;
}
if (rename(temp_path_stub, PRIVATE_STUB_RESOLV_CONF) < 0) {
r = log_error_errno(errno, "Failed to move private stub-resolv.conf file into place: %m");
goto fail;
}
return 0;
fail:
(void) unlink(PRIVATE_UPLINK_RESOLV_CONF);
(void) unlink(temp_path_uplink);
(void) unlink(PRIVATE_STUB_RESOLV_CONF);
(void) unlink(temp_path_stub);
return r;
}
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