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>

1 files changed, 3 insertions, 0 deletions

diff --git a/net/l2tp/l2tp_core.h b/net/l2tp/l2tp_core.h
index 4b9a3b724423..66a559b104b6 100644
--- 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;