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-rw-r--r--NEWS8
-rw-r--r--man/resolved.conf.xml17
-rw-r--r--src/resolve/resolved-dns-transaction.c4
-rw-r--r--src/resolve/resolved-gperf.gperf1
-rw-r--r--src/resolve/resolved-manager.c1
-rw-r--r--src/resolve/resolved-manager.h1
-rw-r--r--src/resolve/resolved.conf.in1
7 files changed, 33 insertions, 0 deletions
diff --git a/NEWS b/NEWS
index 7ecb10e216..e4efb476c6 100644
--- a/NEWS
+++ b/NEWS
@@ -10,6 +10,14 @@ CHANGES WITH 231:
"Options=" with a drop-in, or mount /tmp from /etc/fstab with your
desired options.
+ * systemd-resolved gained a new "Cache=" option in resolved.conf.
+ Local caching makes DNS poisoning attacks slightly easier and allows
+ a local user to detect whether any other user on the same machine has
+ recently visited a given DNS name (privacy). If that is a concern,
+ you can disable local caching with this option at the cost of slower
+ DNS resolution (which is particularly expensive with DNSSEC). The
+ default continues to be "yes" (i. e. caching is enabled).
+
Contributions from: ...
— Somewhere, 2016-XX-XX
diff --git a/man/resolved.conf.xml b/man/resolved.conf.xml
index 920ce9e89b..024ad6a9c1 100644
--- a/man/resolved.conf.xml
+++ b/man/resolved.conf.xml
@@ -202,6 +202,23 @@
</listitem>
</varlistentry>
+ <varlistentry>
+ <term><varname>Cache=</varname></term>
+ <listitem><para>Takes a boolean argument. If "yes" (the default),
+ resolving a domain name which already got queried earlier will re-use
+ the previous result as long as that is still valid, and thus does not
+ need to do an actual network request.</para>
+
+ <para>However, local caching slightly increases the chance of a
+ successful DNS poisoning attack, and might also be a privacy problem in
+ some environments: By measuring the time it takes to resolve a
+ particular network name, a user can determine whether any other user on
+ the same machine recently visited that name. If either of these is a
+ concern, you may disable the local caching. Be aware that this comes at
+ a performance cost, which is <emphasis>very</emphasis> high with DNSSEC.
+ </para></listitem>
+ </varlistentry>
+
</variablelist>
</refsect1>
diff --git a/src/resolve/resolved-dns-transaction.c b/src/resolve/resolved-dns-transaction.c
index 09f60d3e76..06e7145422 100644
--- a/src/resolve/resolved-dns-transaction.c
+++ b/src/resolve/resolved-dns-transaction.c
@@ -590,6 +590,10 @@ static void dns_transaction_cache_answer(DnsTransaction *t) {
if (!IN_SET(t->scope->protocol, DNS_PROTOCOL_DNS, DNS_PROTOCOL_LLMNR))
return;
+ /* Caching disabled? */
+ if (!t->scope->manager->enable_cache)
+ return;
+
/* We never cache if this packet is from the local host, under
* the assumption that a locally running DNS server would
* cache this anyway, and probably knows better when to flush
diff --git a/src/resolve/resolved-gperf.gperf b/src/resolve/resolved-gperf.gperf
index 82f26215df..2fd56bce26 100644
--- a/src/resolve/resolved-gperf.gperf
+++ b/src/resolve/resolved-gperf.gperf
@@ -19,3 +19,4 @@ Resolve.FallbackDNS, config_parse_dns_servers, DNS_SERVER_FALLBACK, 0
Resolve.Domains, config_parse_search_domains, 0, 0
Resolve.LLMNR, config_parse_resolve_support, 0, offsetof(Manager, llmnr_support)
Resolve.DNSSEC, config_parse_dnssec_mode, 0, offsetof(Manager, dnssec_mode)
+Resolve.Cache, config_parse_bool, 0, offsetof(Manager, enable_cache)
diff --git a/src/resolve/resolved-manager.c b/src/resolve/resolved-manager.c
index 30036049da..add463b6a9 100644
--- a/src/resolve/resolved-manager.c
+++ b/src/resolve/resolved-manager.c
@@ -500,6 +500,7 @@ int manager_new(Manager **ret) {
m->llmnr_support = RESOLVE_SUPPORT_YES;
m->mdns_support = RESOLVE_SUPPORT_NO;
m->dnssec_mode = DEFAULT_DNSSEC_MODE;
+ m->enable_cache = true;
m->read_resolv_conf = true;
m->need_builtin_fallbacks = true;
m->etc_hosts_last = m->etc_hosts_mtime = USEC_INFINITY;
diff --git a/src/resolve/resolved-manager.h b/src/resolve/resolved-manager.h
index 114fec7927..deebd8e484 100644
--- a/src/resolve/resolved-manager.h
+++ b/src/resolve/resolved-manager.h
@@ -46,6 +46,7 @@ struct Manager {
ResolveSupport llmnr_support;
ResolveSupport mdns_support;
DnssecMode dnssec_mode;
+ bool enable_cache;
/* Network */
Hashmap *links;
diff --git a/src/resolve/resolved.conf.in b/src/resolve/resolved.conf.in
index a288588924..3bd8389c88 100644
--- a/src/resolve/resolved.conf.in
+++ b/src/resolve/resolved.conf.in
@@ -17,3 +17,4 @@
#Domains=
#LLMNR=yes
#DNSSEC=@DEFAULT_DNSSEC_MODE@
+#Cache=yes