virtio-9p: avoid unwarranted uses of strncpy

In all of these cases, the uses of strncpy were unnecessary, since
at each point of use we know that the NUL-terminated source bytes
fit in the destination buffer.  Use memcpy in place of strncpy.
Acked-by: NAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: NJim Meyering <meyering@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

hw/9pfs/virtio-9p-posix-acl.c

@@ -44,7 +44,8 @@ static ssize_t mp_pacl_listxattr(FsContext *ctx, const char *path,
         return -1;
     }
 
-    strncpy(value, ACL_ACCESS, len);
+    /* len includes the trailing NUL */
+    memcpy(value, ACL_ACCESS, len);
     return 0;
 }
 
@@ -95,7 +96,8 @@ static ssize_t mp_dacl_listxattr(FsContext *ctx, const char *path,
         return -1;
     }
 
-    strncpy(value, ACL_DEFAULT, len);
+    /* len includes the trailing NUL */
+    memcpy(value, ACL_ACCESS, len);
     return 0;
 }
 

hw/9pfs/virtio-9p-xattr-user.c

@@ -61,7 +61,8 @@ static ssize_t mp_user_listxattr(FsContext *ctx, const char *path,
         return -1;
     }
 
-    strncpy(value, name, name_size);
+    /* name_size includes the trailing NUL. */
+    memcpy(value, name, name_size);
     return name_size;
 }
 

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

@@ -53,7 +53,8 @@ ssize_t pt_listxattr(FsContext *ctx, const char *path,
         return -1;
     }
 
-    strncpy(value, name, name_size);
+    /* no need for strncpy: name_size is strlen(name)+1 */
+    memcpy(value, name, name_size);
     return name_size;
 }