sd-radv: Add Router Advertisement DNS Search List option

Add Router Advertisement DNS Search List option as specified
in RFC 8106. The search list option uses and identical option
header as the RDNSS option and therefore the option header
structure can be reused.

If systemd is compiled with IDNA support, internationalization
of the provided search domain is applied, after which the search
list is written in wire format into the DNSSL option.

src/libsystemd-network/radv-internal.h

@@ -36,6 +36,7 @@ assert_cc(SD_RADV_DEFAULT_MIN_TIMEOUT_USEC <= SD_RADV_DEFAULT_MAX_TIMEOUT_USEC)
 #define SD_RADV_MAX_RA_DELAY_TIME_USEC          (500*USEC_PER_MSEC)
 
 #define SD_RADV_OPT_RDNSS                       25
+#define SD_RADV_OPT_DNSSL                       31
 
 enum RAdvState {
         SD_RADV_STATE_IDLE                      = 0,
@@ -75,6 +76,7 @@ struct sd_radv {
 
         size_t n_rdnss;
         struct sd_radv_opt_dns *rdnss;
+        struct sd_radv_opt_dns *dnssl;
 };
 
 struct sd_radv_prefix {

src/libsystemd-network/sd-radv.c

@@ -26,12 +26,14 @@
 
 #include "macro.h"
 #include "alloc-util.h"
+#include "dns-domain.h"
 #include "fd-util.h"
 #include "icmp6-util.h"
 #include "in-addr-util.h"
 #include "radv-internal.h"
 #include "socket-util.h"
 #include "string-util.h"
+#include "strv.h"
 #include "util.h"
 #include "random-util.h"
 
@@ -204,6 +206,12 @@ static int radv_send(sd_radv *ra, const struct in6_addr *dst,
                 msg.msg_iovlen++;
         }
 
+        if (ra->dnssl) {
+                iov[msg.msg_iovlen].iov_base = ra->dnssl;
+                iov[msg.msg_iovlen].iov_len = ra->dnssl->length * 8;
+                msg.msg_iovlen++;
+        }
+
         if (sendmsg(ra->fd, &msg, 0) < 0)
                 return -errno;
 
@@ -590,6 +598,58 @@ _public_ int sd_radv_set_rdnss(sd_radv *ra, uint32_t lifetime,
         return 0;
 }
 
+_public_ int sd_radv_set_dnssl(sd_radv *ra, uint32_t lifetime,
+                               char **search_list) {
+        _cleanup_free_ struct sd_radv_opt_dns *opt_dnssl = NULL;
+        size_t len = 0;
+        char **s;
+        uint8_t *p;
+
+        assert_return(ra, -EINVAL);
+
+        if (!search_list || *search_list == NULL) {
+                ra->dnssl = mfree(ra->dnssl);
+
+                return 0;
+        }
+
+        STRV_FOREACH(s, search_list)
+                len += strlen(*s) + 2;
+
+        len = (sizeof(struct sd_radv_opt_dns) + len + 7) & ~0x7;
+
+        opt_dnssl = malloc0(len);
+        if (!opt_dnssl)
+                return -ENOMEM;
+
+        opt_dnssl->type = SD_RADV_OPT_DNSSL;
+        opt_dnssl->length = len / 8;
+        opt_dnssl->lifetime = htobe32(lifetime);
+
+        p = (uint8_t *)(opt_dnssl + 1);
+        len -= sizeof(struct sd_radv_opt_dns);
+
+        STRV_FOREACH(s, search_list) {
+                int r;
+
+                r = dns_name_to_wire_format(*s, p, len, false);
+                if (r < 0)
+                        return r;
+
+                if (len < (size_t)r)
+                        return -ENOBUFS;
+
+                p += r;
+                len -= r;
+        }
+
+        free(ra->dnssl);
+        ra->dnssl = opt_dnssl;
+        opt_dnssl = NULL;
+
+        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

@@ -59,6 +59,7 @@ 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);
+int sd_radv_set_dnssl(sd_radv *ra, uint32_t lifetime, char **search_list);
 
 /* Advertised prefixes */
 int sd_radv_prefix_new(sd_radv_prefix **ret);