sd-radv: Add Router Advertisement DNS information

Add Router Advertisement Recursive DNS Server information as specified
in RFC 8106.

src/libsystemd-network/radv-internal.h

@@ -35,12 +35,21 @@ assert_cc(SD_RADV_DEFAULT_MIN_TIMEOUT_USEC <= SD_RADV_DEFAULT_MAX_TIMEOUT_USEC)
 #define SD_RADV_MIN_DELAY_BETWEEN_RAS           3
 #define SD_RADV_MAX_RA_DELAY_TIME_USEC          (500*USEC_PER_MSEC)
 
+#define SD_RADV_OPT_RDNSS                       25
+
 enum RAdvState {
         SD_RADV_STATE_IDLE                      = 0,
         SD_RADV_STATE_ADVERTISING               = 1,
 };
 typedef enum RAdvState RAdvState;
 
+struct sd_radv_opt_dns {
+        uint8_t type;
+        uint8_t length;
+        uint16_t reserved;
+        be32_t lifetime;
+} _packed_;
+
 struct sd_radv {
         unsigned n_ref;
         RAdvState state;
@@ -63,6 +72,9 @@ struct sd_radv {
 
         unsigned n_prefixes;
         LIST_HEAD(sd_radv_prefix, prefixes);
+
+        size_t n_rdnss;
+        struct sd_radv_opt_dns *rdnss;
 };
 
 struct sd_radv_prefix {

src/libsystemd-network/sd-radv.c

@@ -126,6 +126,8 @@ _public_ sd_radv *sd_radv_unref(sd_radv *ra) {
                 sd_radv_prefix_unref(p);
         }
 
+        free(ra->rdnss);
+
         radv_reset(ra);
 
         sd_radv_detach_event(ra);
@@ -155,8 +157,8 @@ static int radv_send(sd_radv *ra, const struct in6_addr *dst,
                 .nd_opt_mtu_type = ND_OPT_MTU,
                 .nd_opt_mtu_len = 1,
         };
-        /* Reserve iov space for RA header, linkaddr, MTU + N prefixes */
-        struct iovec iov[3 + ra->n_prefixes];
+        /* Reserve iov space for RA header, linkaddr, MTU, N prefixes, RDNSS */
+        struct iovec iov[4 + ra->n_prefixes];
         struct msghdr msg = {
                 .msg_name = &dst_addr,
                 .msg_namelen = sizeof(dst_addr),
@@ -196,6 +198,12 @@ static int radv_send(sd_radv *ra, const struct in6_addr *dst,
                 msg.msg_iovlen++;
         }
 
+        if (ra->rdnss) {
+                iov[msg.msg_iovlen].iov_base = ra->rdnss;
+                iov[msg.msg_iovlen].iov_len = ra->rdnss->length * 8;
+                msg.msg_iovlen++;
+        }
+
         if (sendmsg(ra->fd, &msg, 0) < 0)
                 return -errno;
 
@@ -546,6 +554,42 @@ _public_ int sd_radv_add_prefix(sd_radv *ra, sd_radv_prefix *p) {
         return 0;
 }
 
+_public_ int sd_radv_set_rdnss(sd_radv *ra, uint32_t lifetime,
+                               const struct in6_addr *dns, size_t n_dns) {
+        _cleanup_free_ struct sd_radv_opt_dns *opt_rdnss = NULL;
+        size_t len;
+
+        assert_return(ra, -EINVAL);
+        assert_return(n_dns < 128, -EINVAL);
+
+        if (!dns || n_dns == 0) {
+                ra->rdnss = mfree(ra->rdnss);
+                ra->n_rdnss = 0;
+
+                return 0;
+        }
+
+        len = sizeof(struct sd_radv_opt_dns) + sizeof(struct in6_addr) * n_dns;
+
+        opt_rdnss = malloc0(len);
+        if (!opt_rdnss)
+                return -ENOMEM;
+
+        opt_rdnss->type = SD_RADV_OPT_RDNSS;
+        opt_rdnss->length = len / 8;
+        opt_rdnss->lifetime = htobe32(lifetime);
+
+        memcpy(opt_rdnss + 1, dns, n_dns * sizeof(struct in6_addr));
+
+        free(ra->rdnss);
+        ra->rdnss = opt_rdnss;
+        opt_rdnss = NULL;
+
+        ra->n_rdnss = n_dns;
+
+        return 0;
+}
+
 _public_ int sd_radv_prefix_new(sd_radv_prefix **ret) {
         _cleanup_(sd_radv_prefix_unrefp) sd_radv_prefix *p = NULL;
 

src/systemd/sd-radv.h

@@ -57,6 +57,8 @@ int sd_radv_set_managed_information(sd_radv *ra, int managed);
 int sd_radv_set_other_information(sd_radv *ra, int other);
 int sd_radv_set_preference(sd_radv *ra, unsigned preference);
 int sd_radv_add_prefix(sd_radv *ra, sd_radv_prefix *p);
+int sd_radv_set_rdnss(sd_radv *ra, uint32_t lifetime,
+                      const struct in6_addr *dns, size_t n_dns);
 
 /* Advertised prefixes */
 int sd_radv_prefix_new(sd_radv_prefix **ret);