From d830ebbdf67d8cb32d33d8fdd47cf467fd6d3815 Mon Sep 17 00:00:00 2001
From: Lennart Poettering <lennart@poettering.net>
Date: Fri, 27 Nov 2015 00:41:32 +0100
Subject: [PATCH] resolved: never cache RRs originating from localhost
After all, this is likely a local DNS forwarder that caches anyway,
hence there's no point in caching twice.
Fixes #2038.
---
src/basic/in-addr-util.c | 15 ++++++++++++++-
src/basic/in-addr-util.h | 1 +
src/resolve/resolved-dns-packet.h | 8 ++++++++
src/resolve/resolved-dns-transaction.c | 3 ++-
4 files changed, 25 insertions(+), 2 deletions(-)
diff --git a/src/basic/in-addr-util.c b/src/basic/in-addr-util.c
index f4e2412..1f61b68 100644
--- a/src/basic/in-addr-util.c
+++ b/src/basic/in-addr-util.c
@@ -44,7 +44,7 @@ int in_addr_is_link_local(int family, const union in_addr_union *u) {
assert(u);
if (family == AF_INET)
- return (be32toh(u->in.s_addr) & 0xFFFF0000) == (169U << 24 | 254U << 16);
+ return (be32toh(u->in.s_addr) & UINT32_C(0xFFFF0000)) == (UINT32_C(169) << 24 | UINT32_C(254) << 16);
if (family == AF_INET6)
return IN6_IS_ADDR_LINKLOCAL(&u->in6);
@@ -52,6 +52,19 @@ int in_addr_is_link_local(int family, const union in_addr_union *u) {
return -EAFNOSUPPORT;
}
+int in_addr_is_localhost(int family, const union in_addr_union *u) {
+ assert(u);
+
+ if (family == AF_INET)
+ /* All of 127.x.x.x is localhost. */
+ return (be32toh(u->in.s_addr) & UINT32_C(0xFF000000)) == UINT32_C(127) << 24;
+
+ if (family == AF_INET6)
+ return IN6_IS_ADDR_LOOPBACK(&u->in6);
+
+ return -EAFNOSUPPORT;
+}
+
int in_addr_equal(int family, const union in_addr_union *a, const union in_addr_union *b) {
assert(a);
assert(b);
diff --git a/src/basic/in-addr-util.h b/src/basic/in-addr-util.h
index 51af088..58f55b3 100644
--- a/src/basic/in-addr-util.h
+++ b/src/basic/in-addr-util.h
@@ -33,6 +33,7 @@ union in_addr_union {
int in_addr_is_null(int family, const union in_addr_union *u);
int in_addr_is_link_local(int family, const union in_addr_union *u);
+int in_addr_is_localhost(int family, const union in_addr_union *u);
int in_addr_equal(int family, const union in_addr_union *a, const union in_addr_union *b);
int in_addr_prefix_intersect(int family, const union in_addr_union *a, unsigned aprefixlen, const union in_addr_union *b, unsigned bprefixlen);
int in_addr_prefix_next(int family, union in_addr_union *u, unsigned prefixlen);
diff --git a/src/resolve/resolved-dns-packet.h b/src/resolve/resolved-dns-packet.h
index 48df5df..90b5a7c 100644
--- a/src/resolve/resolved-dns-packet.h
+++ b/src/resolve/resolved-dns-packet.h
@@ -177,6 +177,14 @@ void dns_packet_rewind(DnsPacket *p, size_t idx);
int dns_packet_skip_question(DnsPacket *p);
int dns_packet_extract(DnsPacket *p);
+static inline bool DNS_PACKET_SHALL_CACHE(DnsPacket *p) {
+ /* Never cache data originating from localhost, under the
+ * assumption, that it's coming from a locally DNS forwarder
+ * or server, that is caching on its own. */
+
+ return in_addr_is_localhost(p->family, &p->sender) == 0;
+}
+
enum {
DNS_RCODE_SUCCESS = 0,
DNS_RCODE_FORMERR = 1,
diff --git a/src/resolve/resolved-dns-transaction.c b/src/resolve/resolved-dns-transaction.c
index c65c9c9..8c4f23a 100644
--- a/src/resolve/resolved-dns-transaction.c
+++ b/src/resolve/resolved-dns-transaction.c
@@ -478,7 +478,8 @@ void dns_transaction_process_reply(DnsTransaction *t, DnsPacket *p) {
}
/* According to RFC 4795, section 2.9. only the RRs from the answer section shall be cached */
- dns_cache_put(&t->scope->cache, t->key, DNS_PACKET_RCODE(p), p->answer, DNS_PACKET_ANCOUNT(p), 0, p->family, &p->sender);
+ if (DNS_PACKET_SHALL_CACHE(p))
+ dns_cache_put(&t->scope->cache, t->key, DNS_PACKET_RCODE(p), p->answer, DNS_PACKET_ANCOUNT(p), 0, p->family, &p->sender);
if (DNS_PACKET_RCODE(p) == DNS_RCODE_SUCCESS)
dns_transaction_complete(t, DNS_TRANSACTION_SUCCESS);