diff options
| -rw-r--r-- | NEWS | 8 | ||||
| -rw-r--r-- | man/resolved.conf.xml | 17 | ||||
| -rw-r--r-- | src/resolve/resolved-dns-transaction.c | 4 | ||||
| -rw-r--r-- | src/resolve/resolved-gperf.gperf | 1 | ||||
| -rw-r--r-- | src/resolve/resolved-manager.c | 1 | ||||
| -rw-r--r-- | src/resolve/resolved-manager.h | 1 | ||||
| -rw-r--r-- | src/resolve/resolved.conf.in | 1 |
7 files changed, 33 insertions, 0 deletions
@@ -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 |