There was a reference counting problem in the TPC logic of net_clone(). net_clone() which is the common logic underlying dup() and dup2() for sockets. When net_clone() calls net_start_monitor() and net_start_monitor() returns a failure (because the underlying TCP connection) then net_clone() must back out the reference count on the structure. Problem noted by Pascal Speck and this implementation of the solution is based on his suggestion.

drivers/mtd/filemtd.c

@@ -585,7 +585,7 @@ FAR struct mtd_dev_s *blockmtd_initialize(FAR const char *path, size_t offset,
  *   Teardown a previously created blockmtd device.
  *
  * Input Parameters:
- *   mtd - Pointer to the mtd.
+ *   dev - Pointer to the mtd driver instance.
  *
  ****************************************************************************/
 
@@ -655,7 +655,7 @@ FAR struct mtd_dev_s *filemtd_initialize(FAR const char *path, size_t offset,
  *   Teardown a previously created filemtd device.
  *
  * Input Parameters:
- *   mtd - Pointer to the mtd.
+ *   dev - Pointer to the mtd driver instance.
  *
  ****************************************************************************/
 

include/nuttx/mtd/mtd.h

@@ -564,7 +564,10 @@ FAR struct mtd_dev_s *n25qxxx_initialize(FAR struct qspi_dev_s *qspi,
  * Name: blockmtd_initialize
  *
  * Description:
- *   Create a block device backed a MTD device.
+ *   Create and initialize a BLOCK MTD device instance.
+ *
+ * Input Parameters:
+ *   path - Path name of the block device backing the MTD device
  *
  ****************************************************************************/
 
@@ -576,7 +579,10 @@ FAR struct mtd_dev_s *blockmtd_initialize(FAR const char *path, size_t offset,
  * Name: blockmtd_teardown
  *
  * Description:
- *   Tear down a blockmtd device.
+ *   Teardown a previously created blockmtd device.
+ *
+ * Input Parameters:
+ *   dev - Pointer to the mtd driver instance.
  *
  ****************************************************************************/
 
@@ -586,7 +592,10 @@ void blockmtd_teardown(FAR struct mtd_dev_s *dev);
  * Name: filemtd_initialize
  *
  * Description:
- *   Create a file backed MTD device.
+ *   Create and initialize a FILE MTD device instance.
+ *
+ * Input Parameters:
+ *   path - Path name of the file backing the MTD device
  *
  ****************************************************************************/
 
@@ -597,17 +606,23 @@ FAR struct mtd_dev_s *filemtd_initialize(FAR const char *path, size_t offset,
  * Name: filemtd_teardown
  *
  * Description:
- *   Tear down a filemtd device.
+ *   Teardown a previously created filemtd device.
+ *
+ * Input Parameters:
+ *   dev - Pointer to the mtd driver instance.
  *
  ****************************************************************************/
 
-void filemtd_teardown(FAR struct mtd_dev_s* mtd);
+void filemtd_teardown(FAR struct mtd_dev_s* dev);
 
 /****************************************************************************
  * Name: filemtd_isfilemtd
  *
  * Description:
- *   Test if MTD is a filemtd device.
+ *   Tests if the provided mtd is a filemtd or blockmtd device.
+ *
+ * Input Parameters:
+ *   mtd - Pointer to the mtd.
  *
  ****************************************************************************/
 

net/socket/net_clone.c

@@ -40,6 +40,7 @@
 #include <nuttx/config.h>
 
 #include <sys/socket.h>
+#include <string.h>
 #include <errno.h>
 #include <debug.h>
 
@@ -47,6 +48,7 @@
 #include <nuttx/net/net.h>
 #include <nuttx/net/udp.h>
 
+#include "inet/inet.h"
 #include "tcp/tcp.h"
 #include "socket/socket.h"
 
@@ -81,7 +83,9 @@ int net_clone(FAR struct socket *psock1, FAR struct socket *psock2)
 
   net_lock();
 
-  /* Duplicate the socket state */
+  /* Duplicate the relevant socket state (zeroing everything else) */
+
+  memset(psock2, 0, sizeof(struct socket));
 
   psock2->s_domain   = psock1->s_domain;    /* IP domain: PF_INET, PF_INET6, or PF_PACKET */
   psock2->s_type     = psock1->s_type;      /* Protocol type: Only SOCK_STREAM or SOCK_DGRAM */
@@ -96,10 +100,6 @@ int net_clone(FAR struct socket *psock1, FAR struct socket *psock2)
 #endif
 #endif
   psock2->s_conn     = psock1->s_conn;      /* UDP or TCP connection structure */
-#ifdef CONFIG_NET_TCP_WRITE_BUFFERS
-  psock2->s_sndcb    = NULL;                /* Force allocation of new callback
-                                             * instance for TCP send */
-#endif
 
   /* Increment the reference count on the socket */
 
@@ -113,14 +113,35 @@ int net_clone(FAR struct socket *psock1, FAR struct socket *psock2)
   psock2->s_sockif->si_addref(psock2);
 
 #ifdef NET_TCP_HAVE_STACK
-  /* For connected socket types, it is necessary to also start the network monitor so
-   * that the newly cloned socket can receive a notification if the network connection
-   * is lost.
+  /* For connected socket types, it is necessary to also start the network
+   * monitor so that the newly cloned socket can receive a notification if
+   * the network connection is lost.
    */
 
   if (psock2->s_type == SOCK_STREAM)
     {
       ret = tcp_start_monitor(psock2);
+
+      /* On failure, back out the reference count on the TCP connection
+       * structure.  tcp_start_monitor() will fail only in the race condition
+       * where the TCP connection has been lost.
+       */
+
+      if (ret < 0)
+        {
+          /* There should be at least two reference counts on the connection
+           * structure:  At least one from the original socket and the one
+           * from above where we incremented the reference count.
+           * inet_close() will handle all cases.
+           *
+           * NOTE:  As a side-effect, inet_close()will also call
+           * tcp_stop_monitor() which could inform the loss of connection to
+           * all open sockets on the connection structure if the reference
+           * count decrements to zero.
+           */
+
+          (void)inet_close(psock2);
+        }
     }
 #endif
 

net/socket/net_dupsd2.c

@@ -89,10 +89,10 @@ int dup2(int sockfd1, int sockfd2)
   psock2 = sockfd_socket(sockfd2);
 
   /* Verify that the sockfd1 and sockfd2 both refer to valid socket
-   * descriptors and that sockfd2 corresponds to allocated socket
+   * descriptors and that sockfd2 corresponds to an allocated socket
    */
 
-  if (!psock1 || !psock2 || psock1->s_crefs <= 0)
+  if (psock1 == NULL || psock2 == NULL || psock1->s_crefs <= 0)
     {
       ret = -EBADF;
       goto errout;