Staging: batman-adv: Reorganize sequence number handling

BATMAN and broadcast packets are tracked with a sequence number window of
currently 64 entries to measure and avoid duplicates. Packets which have a
sequence number smaller than the newest received packet minus 64 are not
within this sequence number window anymore and are called "old packets"
from now on.

When old packets are received, the routing code assumes that the host of the
originator has been restarted. This assumption however might be wrong as
packets can also be delayed by NIC drivers, e.g. because of long queues or
collision detection in dense WiFi? environments. This behaviour can be
reproduced by doing a broadcast ping flood in a dense node environment.

The effect is that the sequence number window is jumping forth and back,
accepting and forwarding any packet (because packets are assumed to be "new")
and causing loops.

To overcome this problem, the sequence number handling has been reorganized.
When an old packet is received, the window is reset back only once. Other old
packets are dropped for (currently) 30 seconds to "protect" the new sequence
number and avoid the hopping as described above.

The reorganization brings some code cleanups (at least i hope you feel the
same) and also fixes a bug in count_real_packets() which falsely updated
the last_real_seqno for slightly older packets within the seqno window
if they are no duplicates.

This second version of the patch also fixes a problem where for seq_diff==64
bit_shift() reads from outside of the seqno window, and removes the loop
for seq_diff == -64 which was present in the first patch.

The third iteration also adds a window for the next expected sequence numbers.
This minimizes sequence number flapping for packets with very big differences
(e.g. 3 packets with seqno 0, 25000 and 50000 might still cause problems
without this window).

Signed-off-by: Simon Wunderlich <siwu@hrz.tu-chemnitz.de>
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 75 insertions, 24 deletions

diff --git a/drivers/staging/batman-adv/routing.c b/drivers/staging/batman-adv/routing.c
index 7b8aa27..bf67059 100644
--- a/drivers/staging/batman-adv/routing.c
+++ b/drivers/staging/batman-adv/routing.c
@@ -304,6 +304,38 @@ update_hna:
 	update_routes(orig_node, orig_node->router, hna_buff, tmp_hna_buff_len);
 }
 
+/* checks whether the host restarted and is in the protection time.
+ * returns:
+ *  0 if the packet is to be accepted
+ *  1 if the packet is to be ignored.
+ */
+static int window_protected(int16_t seq_num_diff,
+				unsigned long *last_reset)
+{
+	if ((seq_num_diff <= -TQ_LOCAL_WINDOW_SIZE)
+		|| (seq_num_diff >= EXPECTED_SEQNO_RANGE)) {
+		if (time_after(jiffies, *last_reset +
+			msecs_to_jiffies(RESET_PROTECTION_MS))) {
+
+			*last_reset = jiffies;
+			bat_dbg(DBG_BATMAN,
+				"old packet received, start protection\n");
+
+			return 0;
+		} else
+			return 1;
+	}
+	return 0;
+}
+
+/* processes a batman packet for all interfaces, adjusts the sequence number and
+ * finds out whether it is a duplicate.
+ * returns:
+ *   1 the packet is a duplicate
+ *   0 the packet has not yet been received
+ *  -1 the packet is old and has been received while the seqno window
+ *     was protected. Caller should drop it.
+ */
 static char count_real_packets(struct ethhdr *ethhdr,
 			       struct batman_packet *batman_packet,
 			       struct batman_if *if_incoming)
@@ -311,31 +343,41 @@ static char count_real_packets(struct ethhdr *ethhdr,
 	struct orig_node *orig_node;
 	struct neigh_node *tmp_neigh_node;
 	char is_duplicate = 0;
-	uint16_t seq_diff;
+	int16_t seq_diff;
+	int need_update = 0;
+	int set_mark;
 
 	orig_node = get_orig_node(batman_packet->orig);
 	if (orig_node == NULL)
 		return 0;
 
+	seq_diff = batman_packet->seqno - orig_node->last_real_seqno;
+
+	/* signalize caller that the packet is to be dropped. */
+	if (window_protected(seq_diff, &orig_node->batman_seqno_reset))
+		return -1;
+
 	list_for_each_entry(tmp_neigh_node, &orig_node->neigh_list, list) {
 
-		if (!is_duplicate)
-			is_duplicate =
-				get_bit_status(tmp_neigh_node->real_bits,
+		is_duplicate |= get_bit_status(tmp_neigh_node->real_bits,
 					       orig_node->last_real_seqno,
 					       batman_packet->seqno);
-		seq_diff = batman_packet->seqno - orig_node->last_real_seqno;
+
 		if (compare_orig(tmp_neigh_node->addr, ethhdr->h_source) &&
 		    (tmp_neigh_node->if_incoming == if_incoming))
-			bit_get_packet(tmp_neigh_node->real_bits, seq_diff, 1);
+			set_mark = 1;
 		else
-			bit_get_packet(tmp_neigh_node->real_bits, seq_diff, 0);
+			set_mark = 0;
+
+		/* if the window moved, set the update flag. */
+		need_update |= bit_get_packet(tmp_neigh_node->real_bits,
+						seq_diff, set_mark);
 
 		tmp_neigh_node->real_packet_count =
 			bit_packet_count(tmp_neigh_node->real_bits);
 	}
 
-	if (!is_duplicate) {
+	if (need_update) {
 		bat_dbg(DBG_BATMAN, "updating last_seqno: old %d, new %d\n",
 			orig_node->last_real_seqno, batman_packet->seqno);
 		orig_node->last_real_seqno = batman_packet->seqno;
@@ -453,24 +495,27 @@ void receive_bat_packet(struct ethhdr *ethhdr,
 		return;
 	}
 
-	if (batman_packet->tq == 0) {
-		count_real_packets(ethhdr, batman_packet, if_incoming);
-
-		bat_dbg(DBG_BATMAN, "Drop packet: originator packet with tq equal 0\n");
-		return;
-	}
-
 	if (is_my_oldorig) {
 		bat_dbg(DBG_BATMAN, "Drop packet: ignoring all rebroadcast echos (sender: %pM)\n", ethhdr->h_source);
 		return;
 	}
 
-	is_duplicate = count_real_packets(ethhdr, batman_packet, if_incoming);
-
 	orig_node = get_orig_node(batman_packet->orig);
 	if (orig_node == NULL)
 		return;
 
+	is_duplicate = count_real_packets(ethhdr, batman_packet, if_incoming);
+
+	if (is_duplicate == -1) {
+		bat_dbg(DBG_BATMAN, "Drop packet: packet within seqno protection time (sender: %pM)\n", ethhdr->h_source);
+		return;
+	}
+
+	if (batman_packet->tq == 0) {
+		bat_dbg(DBG_BATMAN,	"Drop packet: originator packet with tq equal 0\n");
+		return;
+	}
+
 	/* avoid temporary routing loops */
 	if ((orig_node->router) &&
 	    (orig_node->router->orig_node->router) &&
@@ -866,13 +911,13 @@ int recv_unicast_packet(struct sk_buff *skb)
 	return ret;
 }
 
-
 int recv_bcast_packet(struct sk_buff *skb)
 {
 	struct orig_node *orig_node;
 	struct bcast_packet *bcast_packet;
 	struct ethhdr *ethhdr;
 	int hdr_size = sizeof(struct bcast_packet);
+	int16_t seq_diff;
 	unsigned long flags;
 
 	/* drop packet if it has not necessary minimum size */
@@ -908,7 +953,7 @@ int recv_bcast_packet(struct sk_buff *skb)
 		return NET_RX_DROP;
 	}
 
-	/* check flood history */
+	/* check whether the packet is a duplicate */
 	if (get_bit_status(orig_node->bcast_bits,
 			   orig_node->last_bcast_seqno,
 			   ntohs(bcast_packet->seqno))) {
@@ -916,14 +961,20 @@ int recv_bcast_packet(struct sk_buff *skb)
 		return NET_RX_DROP;
 	}
 
-	/* mark broadcast in flood history */
-	if (bit_get_packet(orig_node->bcast_bits,
-			   ntohs(bcast_packet->seqno) -
-			   orig_node->last_bcast_seqno, 1))
+	seq_diff = ntohs(bcast_packet->seqno) - orig_node->last_bcast_seqno;
+
+	/* check whether the packet is old and the host just restarted. */
+	if (window_protected(seq_diff, &orig_node->bcast_seqno_reset)) {
+		spin_unlock_irqrestore(&orig_hash_lock, flags);
+		return NET_RX_DROP;
+	}
+
+	/* mark broadcast in flood history, update window position
+	 * if required. */
+	if (bit_get_packet(orig_node->bcast_bits, seq_diff, 1))
 		orig_node->last_bcast_seqno = ntohs(bcast_packet->seqno);
 
 	spin_unlock_irqrestore(&orig_hash_lock, flags);
-
 	/* rebroadcast packet */
 	add_bcast_packet_to_list(skb);