l2tp: make datapath resilient to packet loss when sequence numbers enabled

If L2TP data sequence numbers are enabled and reordering is not
enabled, data reception stops if a packet is lost since the kernel
waits for a sequence number that is never resent. (When reordering is
enabled, data reception restarts when the reorder timeout expires.) If
no reorder timeout is set, we should count the number of in-sequence
packets after the out-of-sequence (OOS) condition is detected, and reset
sequence number state after a number of such packets are received.

For now, the number of in-sequence packets while in OOS state which
cause the sequence number state to be reset is hard-coded to 5. This
could be configurable later.

Signed-off-by: James Chapman <jchapman@katalix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index 735cc06971ef7a911eaa0778531e78db058f70b1..feae495a0a30accd9eb5a88baf1c23095bb38d66 100644 (file)
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -572,12 +572,33 @@ static int l2tp_recv_data_seq(struct l2tp_session *session, struct sk_buff *skb)
                 * reorder queue, in order of ns.
                 */
                l2tp_recv_queue_skb(session, skb);
+               goto out;
+       }
+
+       /* Packet reordering disabled. Discard out-of-sequence packets, while
+        * tracking the number if in-sequence packets after the first OOS packet
+        * is seen. After nr_oos_count_max in-sequence packets, reset the
+        * sequence number to re-enable packet reception.
+        */
+       if (L2TP_SKB_CB(skb)->ns == session->nr) {
+               skb_queue_tail(&session->reorder_q, skb);
        } else {
-               /* Packet reordering disabled. Discard out-of-sequence
-                * packets
-                */
-               if ((L2TP_SKB_CB(skb)->ns != session->nr) &&
-                   (!session->reorder_skip)) {
+               u32 nr_oos = L2TP_SKB_CB(skb)->ns;
+               u32 nr_next = (session->nr_oos + 1) & session->nr_max;
+
+               if (nr_oos == nr_next)
+                       session->nr_oos_count++;
+               else
+                       session->nr_oos_count = 0;
+
+               session->nr_oos = nr_oos;
+               if (session->nr_oos_count > session->nr_oos_count_max) {
+                       session->reorder_skip = 1;
+                       l2tp_dbg(session, L2TP_MSG_SEQ,
+                                "%s: %d oos packets received. Resetting sequence numbers\n",
+                                session->name, session->nr_oos_count);
+               }
+               if (!session->reorder_skip) {
                        atomic_long_inc(&session->stats.rx_seq_discards);
                        l2tp_dbg(session, L2TP_MSG_SEQ,
                                 "%s: oos pkt %u len %d discarded, waiting for %u, reorder_q_len=%d\n",
@@ -589,6 +610,7 @@ static int l2tp_recv_data_seq(struct l2tp_session *session, struct sk_buff *skb)
                skb_queue_tail(&session->reorder_q, skb);
        }
 
+out:
        return 0;
 
 discard:
@@ -1852,6 +1874,10 @@ struct l2tp_session *l2tp_session_create(int priv_size, struct l2tp_tunnel *tunn
                else
                        session->nr_max = 0xffffff;
                session->nr_window_size = session->nr_max / 2;
+               session->nr_oos_count_max = 4;
+
+               /* Use NR of first received packet */
+               session->reorder_skip = 1;
 
                sprintf(&session->name[0], "sess %u/%u",
                        tunnel->tunnel_id, session->session_id);

diff --git a/net/l2tp/l2tp_core.h b/net/l2tp/l2tp_core.h
index 4b9a3b724423967b2adf24d3f9efa0c7a6f77b9e..66a559b104b6a7af0bc5c76770c32ad0f816670c 100644 (file)
--- a/net/l2tp/l2tp_core.h
+++ b/net/l2tp/l2tp_core.h
@@ -104,6 +104,9 @@ struct l2tp_session {
        struct sk_buff_head     reorder_q;      /* receive reorder queue */
        u32                     nr_max;         /* max NR. Depends on tunnel */
        u32                     nr_window_size; /* NR window size */
+       u32                     nr_oos;         /* NR of last OOS packet */
+       int                     nr_oos_count;   /* For OOS recovery */
+       int                     nr_oos_count_max;
        struct hlist_node       hlist;          /* Hash list node */
        atomic_t                ref_count;