batman-adv: improved gateway tq-based selection

If a client issues a DHCPREQUEST for renewal, the packet is dropped
if the old destination (the old gateway for the client) TQ is smaller
than the current best gateway TQ less GW_THRESHOLD

Signed-off-by: Antonio Quartulli <ordex@autistici.org>
Signed-off-by: Marek Lindner <lindner_marek@yahoo.de>
Signed-off-by: Sven Eckelmann <sven@narfation.org>

1 files changed, 92 insertions, 2 deletions

diff --git a/net/batman-adv/gateway_client.c b/net/batman-adv/gateway_client.c
index 6381864c1ca4..8b25b52a4764 100644
--- a/net/batman-adv/gateway_client.c
+++ b/net/batman-adv/gateway_client.c
@@ -25,11 +25,17 @@
 #include "gateway_common.h"
 #include "hard-interface.h"
 #include "originator.h"
+#include "routing.h"
 #include <linux/ip.h>
 #include <linux/ipv6.h>
 #include <linux/udp.h>
 #include <linux/if_vlan.h>
 
+/* This is the offset of the options field in a dhcp packet starting at
+ * the beginning of the dhcp header */
+#define DHCP_OPTIONS_OFFSET 240
+#define DHCP_REQUEST 3
+
 static void gw_node_free_ref(struct gw_node *gw_node)
 {
         if (atomic_dec_and_test(&gw_node->refcount))
@@ -509,14 +515,75 @@ out:
         return ret;
 }
 
-int gw_is_target(struct bat_priv *bat_priv, struct sk_buff *skb)
+static bool is_type_dhcprequest(struct sk_buff *skb, int header_len)
+{
+        int ret = false;
+        unsigned char *p;
+        int pkt_len;
+
+        if (skb_linearize(skb) < 0)
+                goto out;
+
+        pkt_len = skb_headlen(skb);
+
+        if (pkt_len < header_len + DHCP_OPTIONS_OFFSET + 1)
+                goto out;
+
+        p = skb->data + header_len + DHCP_OPTIONS_OFFSET;
+        pkt_len -= header_len + DHCP_OPTIONS_OFFSET + 1;
+
+        /* Access the dhcp option lists. Each entry is made up by:
+         * - octect 1: option type
+         * - octect 2: option data len (only if type != 255 and 0)
+         * - octect 3: option data */
+        while (*p != 255 && !ret) {
+                /* p now points to the first octect: option type */
+                if (*p == 53) {
+                        /* type 53 is the message type option.
+                         * Jump the len octect and go to the data octect */
+                        if (pkt_len < 2)
+                                goto out;
+                        p += 2;
+
+                        /* check if the message type is what we need */
+                        if (*p == DHCP_REQUEST)
+                                ret = true;
+                        break;
+                } else if (*p == 0) {
+                        /* option type 0 (padding), just go forward */
+                        if (pkt_len < 1)
+                                goto out;
+                        pkt_len--;
+                        p++;
+                } else {
+                        /* This is any other option. So we get the length... */
+                        if (pkt_len < 1)
+                                goto out;
+                        pkt_len--;
+                        p++;
+
+                        /* ...and then we jump over the data */
+                        if (pkt_len < *p)
+                                goto out;
+                        pkt_len -= *p;
+                        p += (*p);
+                }
+        }
+out:
+        return ret;
+}
+
+int gw_is_target(struct bat_priv *bat_priv, struct sk_buff *skb,
+                 struct orig_node *old_gw)
 {
         struct ethhdr *ethhdr;
         struct iphdr *iphdr;
         struct ipv6hdr *ipv6hdr;
         struct udphdr *udphdr;
         struct gw_node *curr_gw;
+        struct neigh_node *neigh_curr = NULL, *neigh_old = NULL;
         unsigned int header_len = 0;
+        int ret = 1;
 
         if (atomic_read(&bat_priv->gw_mode) == GW_MODE_OFF)
                 return 0;
@@ -584,7 +651,30 @@ int gw_is_target(struct bat_priv *bat_priv, struct sk_buff *skb)
         if (!curr_gw)
                 return 0;
 
+        /* If old_gw != NULL then this packet is unicast.
+         * So, at this point we have to check the message type: if it is a
+         * DHCPREQUEST we have to decide whether to drop it or not */
+        if (old_gw && curr_gw->orig_node != old_gw) {
+                if (is_type_dhcprequest(skb, header_len)) {
+                        /* If the dhcp packet has been sent to a different gw,
+                         * we have to evaluate whether the old gw is still
+                         * reliable enough */
+                        neigh_curr = find_router(bat_priv, curr_gw->orig_node,
+                                                 NULL);
+                        neigh_old = find_router(bat_priv, old_gw, NULL);
+                        if (!neigh_curr || !neigh_old)
+                                goto free_neigh;
+                        if (neigh_curr->tq_avg - neigh_old->tq_avg <
+                                                                GW_THRESHOLD)
+                                ret = -1;
+                }
+        }
+free_neigh:
+        if (neigh_old)
+                neigh_node_free_ref(neigh_old);
+        if (neigh_curr)
+                neigh_node_free_ref(neigh_curr);
         if (curr_gw)
                 gw_node_free_ref(curr_gw);
-        return 1;
+        return ret;
 }