Merge pull request #2042 from poettering/resolved-various-3

resolved: Flush caches more agressively, fixes #2038

TODO

@@ -183,16 +183,12 @@ Features:
     we always process them before we process client requests
   - DNSSEC
         - add display of private key types (http://tools.ietf.org/html/rfc4034#appendix-A.1.1)?
-  - DNS
-        - search paths
   - mDNS/DNS-SD
         - mDNS RR resolving
         - service registration
         - service/domain/types browsing
         - avahi compat
   - DNS-SD service registration from socket units
-  - edns0
-  - cname on PTR (?)
   - resolved should optionally register additional per-interface LLMNR
     names, so that for the container case we can establish the same name
     (maybe "host") for referencing the server, everywhere.

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_INET)
+                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);

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);

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,

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);

src/resolve/resolved-resolv-conf.c

@@ -50,9 +50,9 @@ int manager_read_resolv_conf(Manager *m) {
         r = stat("/etc/resolv.conf", &st);
         if (r < 0) {
                 if (errno == ENOENT)
-                        r = 0;
-                else
-                        r = log_warning_errno(errno, "Failed to stat /etc/resolv.conf: %m");
+                        return 0;
+
+                r = log_warning_errno(errno, "Failed to stat /etc/resolv.conf: %m");
                 goto clear;
         }
 
@@ -61,22 +61,18 @@ int manager_read_resolv_conf(Manager *m) {
         if (t == m->resolv_conf_mtime)
                 return 0;
 
-        m->resolv_conf_mtime = t;
-
         /* Is it symlinked to our own file? */
         if (stat("/run/systemd/resolve/resolv.conf", &own) >= 0 &&
             st.st_dev == own.st_dev &&
-            st.st_ino == own.st_ino) {
-                r = 0;
-                goto clear;
-        }
+            st.st_ino == own.st_ino)
+                return 0;
 
         f = fopen("/etc/resolv.conf", "re");
         if (!f) {
                 if (errno == ENOENT)
-                        r = 0;
-                else
-                        r = log_warning_errno(errno, "Failed to open /etc/resolv.conf: %m");
+                        return 0;
+
+                r = log_warning_errno(errno, "Failed to open /etc/resolv.conf: %m");
                 goto clear;
         }
 
@@ -115,6 +111,8 @@ int manager_read_resolv_conf(Manager *m) {
                 }
         }
 
+        m->resolv_conf_mtime = t;
+
         /* 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 */
@@ -131,6 +129,15 @@ int manager_read_resolv_conf(Manager *m) {
          * 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);
+
         return 0;
 
 clear: