[NETROM]: Implement G8PZT Circuit reset for NET/ROM

NET/ROM is lacking a connection reset like TCP's RST flag which at times
may result in a connecting having to slowly timing out instead of just being
reset.  An earlier attempt to reset the connection by sending a
NR_CONNACK | NR_CHOKE_FLAG transport was inacceptable as it did result in
crashes of BPQ systems.  An alternative approach of introducing a new
transport type 7 (NR_RESET) has be implemented several years ago in
Paula Jayne Dowie G8PZT's Xrouter.

Implement NR_RESET for Linux's NET/ROM but like any messing with the state
engine consider this experimental for now and thus control it by a sysctl
(net.netrom.reset) which for the time being defaults to off.

Signed-off-by: Ralf Baechle DL5RB <ralf@linux-mips.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

4 files changed, 41 insertions, 14 deletions

diff --git a/net/netrom/af_netrom.c b/net/netrom/af_netrom.c
index 02b1ab52dbbf..8c3d3a78481e 100644
--- a/net/netrom/af_netrom.c
+++ b/net/netrom/af_netrom.c
@@ -56,6 +56,7 @@ int sysctl_netrom_transport_requested_window_size = NR_DEFAULT_WINDOW;
 int sysctl_netrom_transport_no_activity_timeout   = NR_DEFAULT_IDLE;
 int sysctl_netrom_routing_control                 = NR_DEFAULT_ROUTING;
 int sysctl_netrom_link_fails_count                = NR_DEFAULT_FAILS;
+int sysctl_netrom_reset_circuit                   = NR_DEFAULT_RESET;
 
 static unsigned short circuit = 0x101;
 
@@ -908,17 +909,17 @@ int nr_rx_frame(struct sk_buff *skb, struct net_device *dev)
         if (frametype != NR_CONNREQ) {
                 /*
                  * Here it would be nice to be able to send a reset but
-                 * NET/ROM doesn't have one. The following hack would
-                 * have been a way to extend the protocol but apparently
-                 * it kills BPQ boxes... :-(
+                 * NET/ROM doesn't have one.  We've tried to extend the protocol
+                 * by sending NR_CONNACK | NR_CHOKE_FLAGS replies but that
+                 * apparently kills BPQ boxes... :-(
+                 * So now we try to follow the established behaviour of
+                 * G8PZT's Xrouter which is sending packets with command type 7
+                 * as an extension of the protocol.
                  */
-#if 0
-                /*
-                 * Never reply to a CONNACK/CHOKE.
-                 */
-                if (frametype != NR_CONNACK || flags != NR_CHOKE_FLAG)
-                        nr_transmit_refusal(skb, 1);
-#endif
+                if (sysctl_netrom_reset_circuit &&
+                    (frametype != NR_RESET || flags != 0))
+                        nr_transmit_reset(skb, 1);
+
                 return 0;
         }
 
diff --git a/net/netrom/nr_in.c b/net/netrom/nr_in.c
index 64b81a796907..004e8599b8fe 100644
--- a/net/netrom/nr_in.c
+++ b/net/netrom/nr_in.c
@@ -98,6 +98,11 @@ static int nr_state1_machine(struct sock *sk, struct sk_buff *skb,
                 nr_disconnect(sk, ECONNREFUSED);
                 break;
 
+        case NR_RESET:
+                if (sysctl_netrom_reset_circuit);
+                        nr_disconnect(sk, ECONNRESET);
+                break;
+
         default:
                 break;
         }
@@ -124,6 +129,11 @@ static int nr_state2_machine(struct sock *sk, struct sk_buff *skb,
                 nr_disconnect(sk, 0);
                 break;
 
+        case NR_RESET:
+                if (sysctl_netrom_reset_circuit);
+                        nr_disconnect(sk, ECONNRESET);
+                break;
+
         default:
                 break;
         }
@@ -254,6 +264,11 @@ static int nr_state3_machine(struct sock *sk, struct sk_buff *skb, int frametype
                 }
                 break;
 
+        case NR_RESET:
+                if (sysctl_netrom_reset_circuit);
+                        nr_disconnect(sk, ECONNRESET);
+                break;
+
         default:
                 break;
         }
diff --git a/net/netrom/nr_subr.c b/net/netrom/nr_subr.c
index 587bed2674bf..bcb9946b4f56 100644
--- a/net/netrom/nr_subr.c
+++ b/net/netrom/nr_subr.c
@@ -210,10 +210,9 @@ void nr_write_internal(struct sock *sk, int frametype)
 }
 
 /*
- * This routine is called when a Connect Acknowledge with the Choke Flag
- * set is needed to refuse a connection.
+ * This routine is called to send an error reply.
  */
-void nr_transmit_refusal(struct sk_buff *skb, int mine)
+void __nr_transmit_reply(struct sk_buff *skb, int mine, unsigned char cmdflags)
 {
         struct sk_buff *skbn;
         unsigned char *dptr;
@@ -254,7 +253,7 @@ void nr_transmit_refusal(struct sk_buff *skb, int mine)
                 *dptr++ = 0;
         }
 
-        *dptr++ = NR_CONNACK | NR_CHOKE_FLAG;
+        *dptr++ = cmdflags;
         *dptr++ = 0;
 
         if (!nr_route_frame(skbn, NULL))
diff --git a/net/netrom/sysctl_net_netrom.c b/net/netrom/sysctl_net_netrom.c
index c9ed50382ea7..6bb8dda849dc 100644
--- a/net/netrom/sysctl_net_netrom.c
+++ b/net/netrom/sysctl_net_netrom.c
@@ -30,6 +30,7 @@ static int min_idle[]    = {0 * HZ};
 static int max_idle[]    = {65535 * HZ};
 static int min_route[]   = {0}, max_route[]   = {1};
 static int min_fails[]   = {1}, max_fails[]   = {10};
+static int min_reset[]   = {0}, max_reset[]   = {1};
 
 static struct ctl_table_header *nr_table_header;
 
@@ -155,6 +156,17 @@ static ctl_table nr_table[] = {
                 .extra1         = &min_fails,
                 .extra2         = &max_fails
         },
+        {
+                .ctl_name       = NET_NETROM_RESET,
+                .procname       = "reset",
+                .data           = &sysctl_netrom_reset_circuit,
+                .maxlen         = sizeof(int),
+                .mode           = 0644,
+                .proc_handler   = &proc_dointvec_minmax,
+                .strategy       = &sysctl_intvec,
+                .extra1         = &min_reset,
+                .extra2         = &max_reset
+        },
         { .ctl_name = 0 }
 };