tipc: correct problems with misleading flags returned using poll()

Prevent TIPC from incorrectly setting returned flags to poll()
in the following cases:

- an unconnected socket no longer indicates that it is always readable

- an unconnected, connecting, or listening socket no longer indicates
  that it is always writable

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

1 files changed, 40 insertions, 21 deletions

diff --git a/net/tipc/socket.c b/net/tipc/socket.c
index b89c7b1a0d09..7b81fdd4f6d6 100644
--- a/net/tipc/socket.c
+++ b/net/tipc/socket.c
@@ -429,36 +429,55 @@ static int get_name(struct socket *sock, struct sockaddr *uaddr,
  * to handle any preventable race conditions, so TIPC will do the same ...
  *
  * TIPC sets the returned events as follows:
- * a) POLLRDNORM and POLLIN are set if the socket's receive queue is non-empty
- *    or if a connection-oriented socket is does not have an active connection
- *    (i.e. a read operation will not block).
- * b) POLLOUT is set except when a socket's connection has been terminated
- *    (i.e. a write operation will not block).
- * c) POLLHUP is set when a socket's connection has been terminated.
- *
- * IMPORTANT: The fact that a read or write operation will not block does NOT
- * imply that the operation will succeed!
+ *
+ * socket state         flags set
+ * ------------         ---------
+ * unconnected          no read flags
+ *                      no write flags
+ *
+ * connecting           POLLIN/POLLRDNORM if ACK/NACK in rx queue
+ *                      no write flags
+ *
+ * connected            POLLIN/POLLRDNORM if data in rx queue
+ *                      POLLOUT if port is not congested
+ *
+ * disconnecting        POLLIN/POLLRDNORM/POLLHUP
+ *                      no write flags
+ *
+ * listening            POLLIN if SYN in rx queue
+ *                      no write flags
+ *
+ * ready                POLLIN/POLLRDNORM if data in rx queue
+ * [connectionless]     POLLOUT (since port cannot be congested)
+ *
+ * IMPORTANT: The fact that a read or write operation is indicated does NOT
+ * imply that the operation will succeed, merely that it should be performed
+ * and will not block.
  */
 
 static unsigned int poll(struct file *file, struct socket *sock,
                          poll_table *wait)
 {
         struct sock *sk = sock->sk;
-        u32 mask;
+        u32 mask = 0;
 
         poll_wait(file, sk_sleep(sk), wait);
 
-        if (!skb_queue_empty(&sk->sk_receive_queue) ||
-            (sock->state == SS_UNCONNECTED) ||
-            (sock->state == SS_DISCONNECTING))
-                mask = (POLLRDNORM | POLLIN);
-        else
-                mask = 0;
-
-        if (sock->state == SS_DISCONNECTING)
-                mask |= POLLHUP;
-        else
-                mask |= POLLOUT;
+        switch ((int)sock->state) {
+        case SS_READY:
+        case SS_CONNECTED:
+                if (!tipc_sk_port(sk)->congested)
+                        mask |= POLLOUT;
+                /* fall thru' */
+        case SS_CONNECTING:
+        case SS_LISTENING:
+                if (!skb_queue_empty(&sk->sk_receive_queue))
+                        mask |= (POLLIN | POLLRDNORM);
+                break;
+        case SS_DISCONNECTING:
+                mask = (POLLIN | POLLRDNORM | POLLHUP);
+                break;
+        }
 
         return mask;
 }