dhcpv6-ia: respect prefix assigned to interface (>= /64)

When odhcpd hands out DHCPv6 leases on an interface with a prefix >= /64
(e.g. /96), leases can be outside of the allocated /96 on the interface.
Fixes https://github.com/openwrt/odhcpd/issues/199.

Signed-off-by: Matthias Riegler <[email protected]>
Link: https://github.com/openwrt/odhcpd/pull/219
Signed-off-by: Álvaro Fernández Rojas <[email protected]>

diff --git a/src/dhcpv6-ia.c b/src/dhcpv6-ia.c
index 803d3778995824a045a5cf5d0247058af10bc4d3..e54bc046636ecef997dc028583c1d36e4578f14b 100644 (file)
--- a/src/dhcpv6-ia.c
+++ b/src/dhcpv6-ia.c
@@ -53,6 +53,25 @@ static struct uloop_timeout valid_until_timeout = {.cb = valid_until_cb};
 static uint32_t serial = 0;
 static uint8_t statemd5[16];
 
+static inline uint32_t mask_low_for_hostid(uint8_t dhcpv6_hostid_len)
+{
+       if (dhcpv6_hostid_len >= 32)
+               return UINT32_MAX;
+
+       return (1 << dhcpv6_hostid_len) - 1;
+}
+
+static inline uint32_t mask_high_for_hostid(uint8_t dhcpv6_hostid_len)
+{
+       if (dhcpv6_hostid_len >= 64)
+               return UINT32_MAX;
+
+       if (dhcpv6_hostid_len >= 32)
+               return (1 << (dhcpv6_hostid_len - 32)) - 1;
+
+       return 0;
+}
+
 int dhcpv6_ia_init(void)
 {
        uloop_timeout_set(&valid_until_timeout, 1000);
@@ -223,6 +242,7 @@ void dhcpv6_ia_enum_addrs(struct interface *iface, struct dhcp_assignment *c,
        struct odhcpd_ipaddr *addrs = (c->managed) ? c->managed : iface->addr6;
        size_t addrlen = (c->managed) ? (size_t)c->managed_size : iface->addr6_len;
        size_t m = get_preferred_addr(addrs, addrlen);
+       uint32_t mask_high, mask_low;
 
        for (size_t i = 0; i < addrlen; ++i) {
                struct in6_addr addr;
@@ -249,8 +269,16 @@ void dhcpv6_ia_enum_addrs(struct interface *iface, struct dhcp_assignment *c,
                        if (!ADDR_ENTRY_VALID_IA_ADDR(iface, i, m, addrs))
                                continue;
 
-                       addr.s6_addr32[2] = htonl(c->assigned_host_id >> 32);
-                       addr.s6_addr32[3] = htonl(c->assigned_host_id & UINT32_MAX);
+                       mask_low = mask_low_for_hostid(iface->dhcpv6_hostid_len);
+                       mask_high = mask_high_for_hostid(iface->dhcpv6_hostid_len);
+                       addr.s6_addr32[2] = htonl(
+                               ((c->assigned_host_id >> 32) & mask_high)
+                               & (~mask_high & ntohl(addrs[i].addr.in6.s6_addr32[2]))
+                       );
+                       addr.s6_addr32[3] = htonl(
+                               ((c->assigned_host_id & UINT32_MAX) & mask_low)
+                               & (~mask_low & ntohl(addrs[i].addr.in6.s6_addr32[3]))
+                       );
                } else {
                        if (!valid_prefix_length(c, addrs[i].prefix))
                                continue;
@@ -860,27 +888,22 @@ static bool assign_na(struct interface *iface, struct dhcp_assignment *a)
                uint64_t try;
 
                if (iface->dhcpv6_hostid_len > 32) {
-                       uint32_t mask_high;
-
-                       if (iface->dhcpv6_hostid_len >= 64)
-                               mask_high = UINT32_MAX;
-                       else
-                               mask_high = (1 << (iface->dhcpv6_hostid_len - 32)) - 1;
+                       uint32_t mask_high = mask_high_for_hostid(iface->dhcpv6_hostid_len);
 
                        do {
                                try = (uint32_t)random();
                                try |= (uint64_t)((uint32_t)random() & mask_high) << 32;
                        } while (try < 0x100);
-               } else {
-                       uint32_t mask_low;
 
-                       if (iface->dhcpv6_hostid_len == 32)
-                               mask_low = UINT32_MAX;
-                       else
-                               mask_low = (1 << iface->dhcpv6_hostid_len) - 1;
+               } else {
+                       uint32_t mask_low = mask_low_for_hostid(iface->dhcpv6_hostid_len);
                        do try = ((uint32_t)random()) & mask_low; while (try < 0x100);
                }
 
+               /* If prefix is < 64 bits, we need to shift the interface ID to the left */
+               if (iface->addr6_len < 64)
+                       try <<= (64 - iface->addr6_len);
+
                if (is_reserved_ipv6_iid(try))
                        continue;