1 files changed, 62 insertions, 21 deletions

diff --git a/src/dnsmasq/nm-dnsmasq-utils.c b/src/dnsmasq/nm-dnsmasq-utils.c
index e4f4324b85..cee52c3def 100644
--- a/src/dnsmasq/nm-dnsmasq-utils.c
+++ b/src/dnsmasq/nm-dnsmasq-utils.c
@@ -35,11 +35,12 @@ nm_dnsmasq_utils_get_range (const NMPlatformIP4Address *addr,
 {
 	guint32 host = addr->address;
 	guint8 prefix = addr->plen;
-	guint32 netmask = nm_utils_ip4_prefix_to_netmask (prefix);
-	guint32 first, last, reserved;
+	guint32 netmask;
+	guint32 first, last, mid, reserved;
+	const guint32 NUM = 256;
 
-	g_return_val_if_fail (out_first != NULL, FALSE);
-	g_return_val_if_fail (out_last != NULL, FALSE);
+	g_return_val_if_fail (out_first, FALSE);
+	g_return_val_if_fail (out_last, FALSE);
 
 	if (prefix > 30) {
 		if (out_error_desc)
@@ -47,29 +48,69 @@ nm_dnsmasq_utils_get_range (const NMPlatformIP4Address *addr,
 		return FALSE;
 	}
 
-	/* Find the first available address *after* the local machine's IP */
-	first = (host & netmask) + htonl (1);
+	if (prefix < 24) {
+		/* if the subnet is larger then /24, we partition it and treat it
+		 * like it would be a /24.
+		 *
+		 * Hence, the resulting range will always be between x.x.x.1/24
+		 * and x.x.x.254/24, with x.x.x.0 being the network address of the
+		 * host.
+		 *
+		 * In this case, only a /24 portion of the subnet is used.
+		 * No particular reason for that, but it's unlikely that a user
+		 * would use NetworkManager's shared method when having hundered
+		 * of DHCP clients. So, restrict the range to the same /24 in
+		 * which the host address lies.
+		 */
+		prefix = 24;
+	}
+
+	netmask = nm_utils_ip4_prefix_to_netmask (prefix);
+
+	/* treat addresses in host-order from here on. */
+	netmask = ntohl (netmask);
+	host = ntohl (host);
 
-	/* Shortcut: allow a max of 253 addresses; the - htonl(1) here is to assure
-	 * that we don't set 'last' to the broadcast address of the network. */
-	if (prefix < 24)
-		last = (host | ~nm_utils_ip4_prefix_to_netmask (24)) - htonl (1);
-	else
-		last = (host | ~netmask) - htonl(1);
+	/* if host is the network or broadcast address, coerce it to
+	 * one above or below. Usually, we wouldn't expect the user
+	 * to pick such an address. */
+	if (host == (host & netmask))
+		host++;
+	else if (host == (host | ~netmask))
+		host--;
 
-	/* Figure out which range (either above the host address or below it)
-	 * has more addresses.  Reserve some addresses for static IPs.
+	/* Exclude the network and broadcast address. */
+	first = (host &  netmask) + 1;
+	last =  (host | ~netmask) - 1;
+
+	/* Depending on whether host is above or below the middle of
+	 * the subnet, the larger part if handed out.
+	 *
+	 * If the host is in the lower half, the range starts
+	 * at the lower end with the host (plus reserved), until the
+	 * broadcast address
+	 *
+	 * If the host is in the upper half, the range starts above
+	 * the network-address and goes up until the host (except reserved).
+	 *
+	 * reserved is up to 8 addresses, 10% of the determined range.
 	 */
-	if (ntohl (host) - ntohl (first) > ntohl (last) - ntohl (host)) {
-		/* Range below the host's IP address */
-		reserved = (guint32) ((ntohl (host) - ntohl (first)) / 10);
-		last = host - htonl (MIN (reserved, 8)) - htonl (1);
+	mid =   (host & netmask) | (((first + last) / 2) & ~netmask);
+	if (host > mid) {
+		/* use lower range */
+		reserved = NM_MIN (((host - first) / 10), 8);
+		last = host - 1 - reserved;
+		first = NM_MAX (first, last > NUM ? last - NUM : 0);
 	} else {
-		/* Range above host's IP address */
-		reserved = (guint32) ((ntohl (last) - ntohl (host)) / 10);
-		first = host + htonl (MIN (reserved, 8)) + htonl (1);
+		/* use upper range */
+		reserved = NM_MIN (((last - host) / 10), 8);
+		first = host + 1 + reserved;
+		last = NM_MIN (last, first < 0xFFFFFFFF - NUM ? first + NUM : 0xFFFFFFFF);
 	}
 
+	first = htonl (first);
+	last = htonl (last);
+
 	nm_utils_inet4_ntop (first, out_first);
 	nm_utils_inet4_ntop (last, out_last);