net: take ownership of fd in socket init functions

Today net/socket.c has no consistent policy for closing the socket file
descriptor when initialization fails.  This means we leak the file
descriptor in some cases or we could also try to close it twice.

Make error paths consistent by taking ownership of the file descriptor
and closing it on error.

Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

net/socket.c

@@ -266,14 +266,13 @@ static NetSocketState *net_socket_fd_init_dgram(VLANState *vlan,
             if (saddr.sin_addr.s_addr == 0) {
                 fprintf(stderr, "qemu: error: init_dgram: fd=%d unbound, "
                         "cannot setup multicast dst addr\n", fd);
-                return NULL;
+                goto err;
             }
             /* clone dgram socket */
             newfd = net_socket_mcast_create(&saddr, NULL);
             if (newfd < 0) {
                 /* error already reported by net_socket_mcast_create() */
-                close(fd);
-                return NULL;
+                goto err;
             }
             /* clone newfd to fd, close newfd */
             dup2(newfd, fd);
@@ -283,7 +282,7 @@ static NetSocketState *net_socket_fd_init_dgram(VLANState *vlan,
             fprintf(stderr,
                     "qemu: error: init_dgram: fd=%d failed getsockname(): %s\n",
                     fd, strerror(errno));
-            return NULL;
+            goto err;
         }
     }
 
@@ -304,6 +303,10 @@ static NetSocketState *net_socket_fd_init_dgram(VLANState *vlan,
     if (is_connected) s->dgram_dst=saddr;
 
     return s;
+
+err:
+    closesocket(fd);
+    return NULL;
 }
 
 static void net_socket_connect(void *opaque)
@@ -353,6 +356,7 @@ static NetSocketState *net_socket_fd_init(VLANState *vlan,
         (socklen_t *)&optlen)< 0) {
         fprintf(stderr, "qemu: error: getsockopt(SO_TYPE) for fd=%d failed\n",
                 fd);
+        closesocket(fd);
         return NULL;
     }
     switch(so_type) {
@@ -386,9 +390,7 @@ static void net_socket_accept(void *opaque)
         }
     }
     s1 = net_socket_fd_init(s->vlan, s->model, s->name, fd, 1);
-    if (!s1) {
-        closesocket(fd);
-    } else {
+    if (s1) {
         snprintf(s1->nc.info_str, sizeof(s1->nc.info_str),
                  "socket: connection from %s:%d",
                  inet_ntoa(saddr.sin_addr), ntohs(saddr.sin_port));
@@ -549,7 +551,6 @@ int net_init_socket(QemuOpts *opts,
         }
 
         if (!net_socket_fd_init(vlan, "socket", name, fd, 1)) {
-            close(fd);
             return -1;
         }
     } else if (qemu_opt_get(opts, "listen")) {