tipc: Fix minor bugs in link session number handling

This patch introduces a new, out-of-range value to indicate that
a link endpoint does not have an existing session established
with its peer, eliminating the risk that the previously used
"invalid session number" value (i.e. zero) might eventually be
assigned as a valid session number and cause incorrect link
behavior.

The patch also introduces explicit bit masking when assigning a
new link session number to ensure it does not exceed 16 bits.

Signed-off-by: Allan Stephens <allan.stephens@windriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 12 insertions, 5 deletions

diff --git a/net/tipc/link.c b/net/tipc/link.c
index bd206ebe4eea..b8c1231e3147 100644
--- a/net/tipc/link.c
+++ b/net/tipc/link.c
@@ -51,6 +51,12 @@
 
 
 /*
+ * Out-of-range value for link session numbers
+ */
+
+#define INVALID_SESSION 0x10000
+
+/*
  * Limit for deferred reception queue:
  */
 
@@ -464,7 +470,7 @@ struct link *tipc_link_create(struct bearer *b_ptr, const u32 peer,
         msg = l_ptr->pmsg;
         msg_init(msg, LINK_PROTOCOL, RESET_MSG, TIPC_OK, INT_H_SIZE, l_ptr->addr);
         msg_set_size(msg, sizeof(l_ptr->proto_msg));
-        msg_set_session(msg, tipc_random);
+        msg_set_session(msg, (tipc_random & 0xffff));
         msg_set_bearer_id(msg, b_ptr->identity);
         strcpy((char *)msg_data(msg), if_name);
 
@@ -705,10 +711,10 @@ void tipc_link_reset(struct link *l_ptr)
         u32 checkpoint = l_ptr->next_in_no;
         int was_active_link = tipc_link_is_active(l_ptr);
 
-        msg_set_session(l_ptr->pmsg, msg_session(l_ptr->pmsg) + 1);
+        msg_set_session(l_ptr->pmsg, ((msg_session(l_ptr->pmsg) + 1) & 0xffff));
 
-        /* Link is down, accept any session: */
-        l_ptr->peer_session = 0;
+        /* Link is down, accept any session */
+        l_ptr->peer_session = INVALID_SESSION;
 
         /* Prepare for max packet size negotiation */
         link_init_max_pkt(l_ptr);
@@ -2275,7 +2281,8 @@ static void link_recv_proto_msg(struct link *l_ptr, struct sk_buff *buf)
         switch (msg_type(msg)) {
 
         case RESET_MSG:
-                if (!link_working_unknown(l_ptr) && l_ptr->peer_session) {
+                if (!link_working_unknown(l_ptr) &&
+                    (l_ptr->peer_session != INVALID_SESSION)) {
                         if (msg_session(msg) == l_ptr->peer_session) {
                                 dbg("Duplicate RESET: %u<->%u\n",
                                     msg_session(msg), l_ptr->peer_session);