RFC 3927 Section 2.1 states that the random number generator should be

seeded with a known value derived from the IEEE 802 MAC address and that
the first 256 and last 256 addresses are reserved for future use.

diff --git a/dhcp.h b/dhcp.h
index 7141023578e72c008c26d606cb8b05f2f3f5eb3f..48e1bba0e772dbd8ab321c169b3ef97713c529da 100644 (file)
--- a/dhcp.h
+++ b/dhcp.h
@@ -212,13 +212,18 @@ struct dhcp_state {
        time_t nakoff;
        uint32_t xid;
        int socket;
+
+       /* ARP */
        int probes;
        int claims;
-       int conflicts;
-       time_t defend;
        struct in_addr fail;
        size_t arping_index;
 
+       /* IPv4LL */
+       char randomstate[128];
+       int conflicts;
+       time_t defend;
+
        int raw_fd;
        int arp_fd;
        size_t buffer_size, buffer_len, buffer_pos;

diff --git a/ipv4ll.c b/ipv4ll.c
index ab4b5c0886c87f0874182d5bb3ddb1595fbd67db..bc37e3760dd4a4056a6969b713f28841eb7b64e1 100644 (file)
--- a/ipv4ll.c
+++ b/ipv4ll.c
@@ -71,29 +71,36 @@ ipv4ll_make_lease(uint32_t addr)
 }
 
 static struct dhcp_message *
-ipv4ll_find_lease(struct dhcpcd_ctx *ctx)
+ipv4ll_find_lease(const struct interface *ifp)
 {
        uint32_t addr;
-       struct interface *ifp;
+       struct interface *ifp2;
        const struct dhcp_state *state;
 
        for (;;) {
-               addr = ntohl(LINKLOCAL_ADDR |
-                   (uint32_t)(abs((int)arc4random_uniform(0xFD00)) + 0x0100));
+               addr = ntohl(LINKLOCAL_ADDR | random() & 0x0000FFFF);
 
-               /* Sanity */
-               if (!IN_LINKLOCAL(htonl(addr)))
+               state = D_CSTATE(ifp);
+               /* No point using a failed address */
+               if (addr == state->fail.s_addr)
+                       continue;
+
+               /* RFC 3927 Section 2.1 states that the first 256 and
+                * last 256 addresses are reserved for future use */
+               if (!IN_LINKLOCAL(htonl(addr)) ||
+                   (htonl(addr) & 0x0000FF00) == 0x0000 ||
+                   (htonl(addr) & 0x0000FF00) == 0xFF00)
                        continue;
 
                /* Ensure we don't have the address on another interface */
-               TAILQ_FOREACH(ifp, ctx->ifaces, next) {
-                       state = D_CSTATE(ifp);
+               TAILQ_FOREACH(ifp2, ifp->ctx->ifaces, next) {
+                       state = D_CSTATE(ifp2);
                        if (state && state->addr.s_addr == addr)
                                break;
                }
 
                /* Yay, this should be a unique and workable IPv4LL address */
-               if (ifp == NULL)
+               if (ifp2 == NULL)
                        break;
        }
        return ipv4ll_make_lease(addr);
@@ -115,6 +122,21 @@ ipv4ll_start(void *arg)
        struct dhcp_state *state = D_STATE(ifp);
        uint32_t addr;
 
+       /* RFC 3927 Section 2.1 states that the random number generator
+        * SHOULD be seeded with a value derived from persistent information
+        * such as the IEEE 802 MAC address. */
+       if (state->conflicts == 0) {
+               unsigned int seed;
+
+               if (sizeof(seed) > ifp->hwlen) {
+                       seed = 0;
+                       memcpy(&seed, ifp->hwaddr, ifp->hwlen);
+               } else
+                       memcpy(&seed, ifp->hwaddr + ifp->hwlen - sizeof(seed),
+                           sizeof(seed));
+               initstate(seed, state->randomstate, sizeof(state->randomstate));
+       }
+
        eloop_timeout_delete(ifp->ctx->eloop, NULL, ifp);
        state->probes = 0;
        state->claims = 0;
@@ -133,6 +155,7 @@ ipv4ll_start(void *arg)
        }
 
        state->state = DHS_INIT_IPV4LL;
+       setstate(state->randomstate);
        /* We maybe rebooting an IPv4LL address. */
        if (!IN_LINKLOCAL(htonl(addr))) {
                syslog(LOG_INFO, "%s: probing for an IPv4LL address",
@@ -140,15 +163,15 @@ ipv4ll_start(void *arg)
                addr = 0;
        }
        if (addr == 0)
-               state->offer = ipv4ll_find_lease(ifp->ctx);
+               state->offer = ipv4ll_find_lease(ifp);
        else
                state->offer = ipv4ll_make_lease(addr);
-       if (state->offer == NULL)
+       if (state->offer == NULL) {
                syslog(LOG_ERR, "%s: %m", __func__);
-       else {
-               state->lease.frominfo = 0;
-               arp_probe(ifp);
+               return;
        }
+       state->lease.frominfo = 0;
+       arp_probe(ifp);
 }
 
 void