hw/9pfs: avoid buffer overrun

v9fs_add_dir_node and qemu_v9fs_synth_add_file used strncpy
to form node->name, which requires NUL-termination, but
strncpy does not ensure NUL-termination.
Use pstrcpy, which does.

Acked-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Jim Meyering <meyering@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

hw/9pfs/virtio-9p-synth.c

diff --git a/hw/9pfs/virtio-9p-synth.c b/hw/9pfs/virtio-9p-synth.c
index 92e0b09..e95a856 100644
--- a/hw/9pfs/virtio-9p-synth.c
+++ b/hw/9pfs/virtio-9p-synth.c
@@ -58,7 +58,7 @@
         node->attr->read  = NULL;
     }
     node->private = node;
-    strncpy(node->name, name, sizeof(node->name));
+    pstrcpy(node->name, sizeof(node->name), name);
     QLIST_INSERT_HEAD_RCU(&parent->child, node, sibling);
     return node;
 }
@@ -132,7 +132,7 @@
     node->attr->write  = write;
     node->attr->mode   = mode;
     node->private      = arg;
-    strncpy(node->name, name, sizeof(node->name));
+    pstrcpy(node->name, sizeof(node->name), name);
     QLIST_INSERT_HEAD_RCU(&parent->child, node, sibling);
     ret = 0;
 err_out: