Merge pull request #18896 from poettering/no-localhost-ipv6

if ipv6 is turned off, don't synthesize localhost as ::1 ever

src/basic/meson.build

@@ -235,6 +235,8 @@ basic_sources = files('''
         strv.h
         strxcpyx.c
         strxcpyx.h
+        sysctl-util.c
+        sysctl-util.h
         syslog-util.c
         syslog-util.h
         terminal-util.c

src/basic/socket-util.c

@@ -31,6 +31,7 @@
 #include "string-table.h"
 #include "string-util.h"
 #include "strv.h"
+#include "sysctl-util.h"
 #include "user-util.h"
 #include "utf8.h"
 
@@ -277,10 +278,48 @@ const char* socket_address_get_path(const SocketAddress *a) {
 }
 
 bool socket_ipv6_is_supported(void) {
-        if (access("/proc/net/if_inet6", F_OK) != 0)
+        static int cached = -1;
+
+        if (cached < 0) {
+
+                if (access("/proc/net/if_inet6", F_OK) < 0) {
+
+                        if (errno != ENOENT) {
+                                log_debug_errno(errno, "Unexpected error when checking whether /proc/net/if_inet6 exists: %m");
+                                return false;
+                        }
+
+                        cached = false;
+                } else
+                        cached = true;
+        }
+
+        return cached;
+}
+
+bool socket_ipv6_is_enabled(void) {
+        _cleanup_free_ char *v;
+        int r;
+
+        /* Much like socket_ipv6_is_supported(), but also checks that the sysctl that disables IPv6 on all
+         * interfaces isn't turned on */
+
+        if (!socket_ipv6_is_supported())
                 return false;
 
-        return true;
+        r = sysctl_read_ip_property(AF_INET6, "all", "disable_ipv6", &v);
+        if (r < 0) {
+                log_debug_errno(r, "Unexpected error reading 'net.ipv6.conf.all.disable_ipv6' sysctl: %m");
+                return true;
+        }
+
+        r = parse_boolean(v);
+        if (r < 0) {
+                log_debug_errno(r, "Failed to pare 'net.ipv6.conf.all.disable_ipv6' sysctl: %m");
+                return true;
+        }
+
+        return !r;
 }
 
 bool socket_address_matches_fd(const SocketAddress *a, int fd) {

src/basic/socket-util.h

@@ -101,6 +101,7 @@ bool socket_address_equal(const SocketAddress *a, const SocketAddress *b) _pure_
 const char* socket_address_get_path(const SocketAddress *a);
 
 bool socket_ipv6_is_supported(void);
+bool socket_ipv6_is_enabled(void);
 
 int sockaddr_port(const struct sockaddr *_sa, unsigned *port);
 const union in_addr_union *sockaddr_in_addr(const struct sockaddr *sa);

src/basic/sysctl-util.c

@@ -96,14 +96,14 @@ int sysctl_write_ip_property(int af, const char *ifname, const char *property, c
         return write_string_file(p, value, WRITE_STRING_FILE_VERIFY_ON_FAILURE | WRITE_STRING_FILE_DISABLE_BUFFER);
 }
 
-int sysctl_read(const char *property, char **content) {
+int sysctl_read(const char *property, char **ret) {
         char *p;
 
         assert(property);
-        assert(content);
+        assert(ret);
 
         p = strjoina("/proc/sys/", property);
-        return read_full_file(p, content, NULL);
+        return read_full_virtual_file(p, ret, NULL);
 }
 
 int sysctl_read_ip_property(int af, const char *ifname, const char *property, char **ret) {
@@ -118,7 +118,7 @@ int sysctl_read_ip_property(int af, const char *ifname, const char *property, ch
                      ifname ? "/conf/" : "", strempty(ifname),
                      property[0] == '/' ? "" : "/", property);
 
-        r = read_one_line_file(p, &value);
+        r = read_full_virtual_file(p, &value, NULL);
         if (r < 0)
                 return r;
 

src/resolve/resolved-dns-synthesize.c

@@ -81,7 +81,7 @@ static int synthesize_localhost_rr(Manager *m, const DnsResourceKey *key, int if
                         return r;
         }
 
-        if (IN_SET(key->type, DNS_TYPE_AAAA, DNS_TYPE_ANY)) {
+        if (IN_SET(key->type, DNS_TYPE_AAAA, DNS_TYPE_ANY) && socket_ipv6_is_enabled()) {
                 _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
 
                 rr = dns_resource_record_new_full(DNS_CLASS_IN, DNS_TYPE_AAAA, dns_resource_key_name(key));
@@ -234,7 +234,7 @@ static int synthesize_system_hostname_rr(Manager *m, const DnsResourceKey *key,
                                         .address.in.s_addr = htobe32(0x7F000002),
                                 };
 
-                        if (IN_SET(af, AF_INET6, AF_UNSPEC))
+                        if (IN_SET(af, AF_INET6, AF_UNSPEC) && socket_ipv6_is_enabled())
                                 buffer[n++] = (struct local_address) {
                                         .family = AF_INET6,
                                         .ifindex = dns_synthesize_ifindex(ifindex),

src/shared/meson.build

@@ -244,8 +244,6 @@ shared_sources = files('''
         specifier.h
         switch-root.c
         switch-root.h
-        sysctl-util.c
-        sysctl-util.h
         tmpfile-util-label.c
         tmpfile-util-label.h
         tomoyo-util.c

src/test/test-socket-util.c

@@ -504,6 +504,11 @@ static void test_flush_accept(void) {
         assert_se(flush_accept(listen_seqpacket) >= 0);
 }
 
+static void test_ipv6_enabled(void) {
+        log_info("IPv6 supported: %s", yes_no(socket_ipv6_is_supported()));
+        log_info("IPv6 enabled: %s", yes_no(socket_ipv6_is_enabled()));
+}
+
 int main(int argc, char *argv[]) {
         test_setup_logging(LOG_DEBUG);
 
@@ -519,6 +524,7 @@ int main(int argc, char *argv[]) {
         test_send_nodata_nofd();
         test_send_emptydata();
         test_flush_accept();
+        test_ipv6_enabled();
 
         return 0;
 }