From 68e9ba58d39a442c1f0f55cd35de6f0e69345950 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Petr=20Men=C5=A1=C3=ADk?= <pemensik@redhat.com>
Date: Tue, 5 Oct 2021 13:46:51 +0200
Subject: [PATCH] Introduce new --local-service=host parameter
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Similar to local-service, but more strict. Listen only on localhost
unless other interface is specified. Has no effect when interface is
provided explicitly. I had multiple bugs fillen on Fedora, because I have
changed default configuration to:
interface=lo
bind-interfaces
People just adding configuration parts to /etc/dnsmasq.d or appending to
existing configuration often fail to see some defaults are already there.
Give them auto-ignored configuration as smart default.
Signed-off-by: Petr Menšík <pemensik@redhat.com>
Do not add a new parameter on command line. Instead add just parameter
for behaviour modification of existing local-service option. Now it
accepts two optional values:
- net: exactly the same as before
- host: bind only to lo interface, do not listen on any other addresses
than loopback.
---
man/dnsmasq.8 | 8 +++++---
src/dnsmasq.c | 2 ++
src/dnsmasq.h | 3 ++-
src/option.c | 44 +++++++++++++++++++++++++++++++++-----------
4 files changed, 42 insertions(+), 15 deletions(-)
diff --git a/man/dnsmasq.8 b/man/dnsmasq.8
index e21bd09..855eda6 100644
--- a/man/dnsmasq.8
+++ b/man/dnsmasq.8
@@ -270,14 +270,16 @@ the address dnsmasq is listening on. When an interface is specified,
it may be qualified with "/4" or "/6" to specify only the IPv4 or IPv6
addresses associated with the interface. Since any defined authoritative zones are also available as part of the normal recusive DNS service supplied by dnsmasq, it can make sense to have an --auth-server declaration with no interfaces or address, but simply specifying the primary external nameserver.
.TP
-.B --local-service
+.B --local-service[=net|host]
+Without parameter or with net parameter, restricts service to connected network.
Accept DNS queries only from hosts whose address is on a local subnet,
-ie a subnet for which an interface exists on the server. This option
+ie a subnet for which an interface exists on the server. With host parameter, listens
+only on lo interface and accepts queries from localhost only. This option
only has effect if there are no \fB--interface\fP, \fB--except-interface\fP,
\fB--listen-address\fP or \fB--auth-server\fP options. It is intended to be set as
a default on installation, to allow unconfigured installations to be
useful but also safe from being used for DNS amplification attacks.
-.TP
+.TP
.B \-2, --no-dhcp-interface=<interface name>
Do not provide DHCP or TFTP on the specified interface, but do provide DNS service.
.TP
diff --git a/src/dnsmasq.c b/src/dnsmasq.c
index 14fe368..0b34627 100644
--- a/src/dnsmasq.c
+++ b/src/dnsmasq.c
@@ -864,6 +864,8 @@ int main (int argc, char **argv)
if (option_bool(OPT_LOCAL_SERVICE))
my_syslog(LOG_INFO, _("DNS service limited to local subnets"));
+ else if (option_bool(OPT_LOCALHOST_SERVICE))
+ my_syslog(LOG_INFO, _("DNS service limited to localhost"));
}
my_syslog(LOG_INFO, _("compile time options: %s"), compile_opts);
diff --git a/src/dnsmasq.h b/src/dnsmasq.h
index fe9aa07..1fabc22 100644
--- a/src/dnsmasq.h
+++ b/src/dnsmasq.h
@@ -282,7 +282,8 @@ struct event_desc {
#define OPT_STRIP_MAC 70
#define OPT_NORR 71
#define OPT_NO_IDENT 72
-#define OPT_LAST 73
+#define OPT_LOCALHOST_SERVICE 73
+#define OPT_LAST 74
#define OPTION_BITS (sizeof(unsigned int)*8)
#define OPTION_SIZE ( (OPT_LAST/OPTION_BITS)+((OPT_LAST%OPTION_BITS)!=0) )
diff --git a/src/option.c b/src/option.c
index e4810fd..70cece6 100644
--- a/src/option.c
+++ b/src/option.c
@@ -217,7 +217,7 @@ static const struct myoption opts[] =
{ "domain-suffix", 1, 0, 's' },
{ "interface", 1, 0, 'i' },
{ "listen-address", 1, 0, 'a' },
- { "local-service", 0, 0, LOPT_LOCAL_SERVICE },
+ { "local-service", 2, 0, LOPT_LOCAL_SERVICE },
{ "bogus-priv", 0, 0, 'b' },
{ "bogus-nxdomain", 1, 0, 'B' },
{ "ignore-address", 1, 0, LOPT_IGNORE_ADDR },
@@ -560,7 +560,7 @@ static struct {
{ LOPT_QUIET_DHCP6, OPT_QUIET_DHCP6, NULL, gettext_noop("Do not log routine DHCPv6."), NULL },
{ LOPT_QUIET_RA, OPT_QUIET_RA, NULL, gettext_noop("Do not log RA."), NULL },
{ LOPT_LOG_DEBUG, OPT_LOG_DEBUG, NULL, gettext_noop("Log debugging information."), NULL },
- { LOPT_LOCAL_SERVICE, OPT_LOCAL_SERVICE, NULL, gettext_noop("Accept queries only from directly-connected networks."), NULL },
+ { LOPT_LOCAL_SERVICE, ARG_ONE, NULL, gettext_noop("Accept queries only from directly-connected networks."), NULL },
{ LOPT_LOOP_DETECT, OPT_LOOP_DETECT, NULL, gettext_noop("Detect and remove DNS forwarding loops."), NULL },
{ LOPT_IGNORE_ADDR, ARG_DUP, "<ipaddr>", gettext_noop("Ignore DNS responses containing ipaddr."), NULL },
{ LOPT_DHCPTTL, ARG_ONE, "<ttl>", gettext_noop("Set TTL in DNS responses with DHCP-derived addresses."), NULL },
@@ -1390,6 +1390,16 @@ static void dhcp_opt_free(struct dhcp_opt *opt)
free(opt);
}
+static void if_names_add(const char *ifname)
+{
+ struct iname *new = opt_malloc(sizeof(struct iname));
+ new->next = daemon->if_names;
+ daemon->if_names = new;
+ /* new->name may be NULL if someone does
+ "interface=" to disable all interfaces except loop. */
+ new->name = opt_string_alloc(ifname);
+ new->used = 0;
+}
/* This is too insanely large to keep in-line in the switch */
static int parse_dhcp_opt(char *errstr, char *arg, int flags)
@@ -2811,14 +2821,8 @@ static int one_opt(int option, char *arg, char *errstr, char *gen_err, int comma
case 'i': /* --interface */
do {
- struct iname *new = opt_malloc(sizeof(struct iname));
- comma = split(arg);
- new->next = daemon->if_names;
- daemon->if_names = new;
- /* new->name may be NULL if someone does
- "interface=" to disable all interfaces except loop. */
- new->name = opt_string_alloc(arg);
- new->used = 0;
+ comma = split(arg);
+ if_names_add(arg);
arg = comma;
} while (arg);
break;
@@ -3377,6 +3381,15 @@ static int one_opt(int option, char *arg, char *errstr, char *gen_err, int comma
ret_err(gen_err);
else if (daemon->max_logs > 100)
daemon->max_logs = 100;
+ break;
+
+ case LOPT_LOCAL_SERVICE: /* --local-service */
+ if (!arg || !strcmp(arg, "net"))
+ set_option_bool(OPT_LOCAL_SERVICE);
+ else if (!strcmp(arg, "host"))
+ set_option_bool(OPT_LOCALHOST_SERVICE);
+ else
+ ret_err(gen_err);
break;
case 'P': /* --edns-packet-max */
@@ -6056,7 +6069,16 @@ void read_opts(int argc, char **argv, char *compile_opts)
/* If there's access-control config, then ignore --local-service, it's intended
as a system default to keep otherwise unconfigured installations safe. */
if (daemon->if_names || daemon->if_except || daemon->if_addrs || daemon->authserver)
- reset_option_bool(OPT_LOCAL_SERVICE);
+ {
+ reset_option_bool(OPT_LOCAL_SERVICE);
+ reset_option_bool(OPT_LOCALHOST_SERVICE);
+ }
+ else if (option_bool(OPT_LOCALHOST_SERVICE) && !option_bool(OPT_LOCAL_SERVICE))
+ {
+ /* listen only on localhost, emulate --interface=lo --bind-interfaces */
+ if_names_add(NULL);
+ set_option_bool(OPT_NOWILD);
+ }
if (testmode)
{
--
2.43.0