DHCP: Handle option 108 correctly when receiving 0.0.0.0 OFFER (#342)

* DHCP: Handle option 108 correctly when receiving 0.0.0.0 OFFER

According to RFC8925 section 3.3.1, when the server supports both option
108 (IPv6-Only Preferred) and option 116 (Auto-Configure), and the
client only sends IPv6-Only Preferred option, then the server SHOULD
return 0.0.0.0 as the offered address, and not setting the
Auto-Configure option.

However, in our current client code, the IPv6-Only Preferred option in a
0.0.0.0 OFFER is only handled correctly when the Auto-Configure option
is present. This patch fixes this issue.

---------

Co-authored-by: Roy Marples <roy@marples.name>

diff --git a/src/dhcp.c b/src/dhcp.c
index 0fea3351786d6ebd36f02f71dde31dda222b52d7..0267a2a9fb292d7cfbe460a0ffa7691f83f2fbab 100644 (file)
--- a/src/dhcp.c
+++ b/src/dhcp.c
@@ -774,7 +774,7 @@ make_message(struct bootp **bootpm, const struct interface *ifp, uint8_t type)
        }
 
        if (ifo->options & DHCPCD_BROADCAST &&
-           bootp->ciaddr == 0 &&
+           bootp->ciaddr == INADDR_ANY &&
            type != DHCP_DECLINE &&
            type != DHCP_RELEASE)
                bootp->flags = htons(BROADCAST_FLAG);
@@ -1651,7 +1651,7 @@ dhcp_makeudppacket(size_t *sz, const uint8_t *data, size_t length,
 
        ip->ip_p = IPPROTO_UDP;
        ip->ip_src.s_addr = source.s_addr;
-       if (dest.s_addr == 0)
+       if (dest.s_addr == INADDR_ANY)
                ip->ip_dst.s_addr = INADDR_BROADCAST;
        else
                ip->ip_dst.s_addr = dest.s_addr;
@@ -2995,7 +2995,7 @@ dhcp_handledhcp(struct interface *ifp, struct bootp *bootp, size_t bootp_len,
        char *msg;
        bool bootp_copied;
        uint32_t v6only_time = 0;
-       bool use_v6only = false;
+       bool use_v6only = false, has_auto_conf = false;
 #ifdef AUTH
        const uint8_t *auth;
        size_t auth_len;
@@ -3215,7 +3215,8 @@ dhcp_handledhcp(struct interface *ifp, struct bootp *bootp, size_t bootp_len,
 
        if (has_option_mask(ifo->requestmask, DHO_IPV6_PREFERRED_ONLY)) {
                if (get_option_uint32(ifp->ctx, &v6only_time, bootp, bootp_len,
-                   DHO_IPV6_PREFERRED_ONLY) == 0 && (state->state == DHS_DISCOVER ||
+                   DHO_IPV6_PREFERRED_ONLY) == 0 &&
+                   (state->state == DHS_DISCOVER ||
                    state->state == DHS_REBOOT || state->state == DHS_NONE))
                {
                        char v6msg[128];
@@ -3231,8 +3232,8 @@ dhcp_handledhcp(struct interface *ifp, struct bootp *bootp, size_t bootp_len,
        }
 
        /* DHCP Auto-Configure, RFC 2563 */
-       if (type == DHCP_OFFER && bootp->yiaddr == 0) {
-               LOGDHCP(LOG_WARNING, "no address given");
+       if (type == DHCP_OFFER && bootp->yiaddr == INADDR_ANY) {
+               LOGDHCP(LOG_WARNING, "no address offered");
                if ((msg = get_option_string(ifp->ctx,
                    bootp, bootp_len, DHO_MESSAGE)))
                {
@@ -3244,6 +3245,7 @@ dhcp_handledhcp(struct interface *ifp, struct bootp *bootp, size_t bootp_len,
                    get_option_uint8(ifp->ctx, &tmp, bootp, bootp_len,
                    DHO_AUTOCONFIGURE) == 0)
                {
+                       has_auto_conf = true;
                        switch (tmp) {
                        case 0:
                                LOGDHCP(LOG_WARNING, "IPv4LL disabled from");
@@ -3262,24 +3264,27 @@ dhcp_handledhcp(struct interface *ifp, struct bootp *bootp, size_t bootp_len,
                                    ifp->name, tmp);
                                break;
                        }
-                       eloop_timeout_delete(ifp->ctx->eloop, NULL, ifp);
-                       eloop_timeout_add_sec(ifp->ctx->eloop,
-                           use_v6only ? v6only_time : DHCP_MAX,
-                           dhcp_discover, ifp);
                }
 #endif
-               return;
        }
 
        if (use_v6only) {
                dhcp_drop(ifp, "EXPIRE");
                dhcp_unlink(ifp->ctx, state->leasefile);
+       }
+       if (use_v6only || has_auto_conf) {
                eloop_timeout_delete(ifp->ctx->eloop, NULL, ifp);
-               eloop_timeout_add_sec(ifp->ctx->eloop, v6only_time,
+               eloop_timeout_add_sec(ifp->ctx->eloop,
+                   use_v6only ? v6only_time : DHCP_MAX,
                    dhcp_discover, ifp);
                return;
        }
 
+       /* No hints as what to do with no address?
+        * All we can do is continue. */
+       if (type == DHCP_OFFER && bootp->yiaddr == INADDR_ANY)
+               return;
+
        /* Ensure that the address offered is valid */
        if ((type == 0 || type == DHCP_OFFER || type == DHCP_ACK) &&
            (bootp->ciaddr == INADDR_ANY || bootp->ciaddr == INADDR_BROADCAST)