[bug report] usb: gadget: f_fs: OS descriptors support

[bug report] usb: gadget: f_fs: OS descriptors support

[Dan Carpenter]

Hello Andrzej Pietrasiewicz,

The patch f0175ab51993: "usb: gadget: f_fs: OS descriptors support"
from Jul 9, 2014, leads to the following static checker warning:

	drivers/usb/gadget/function/f_fs.c:2992 __ffs_func_bind_do_os_desc()
	error: 'ext_prop->data_len' from user is not capped properly

drivers/usb/gadget/function/f_fs.c
  2961                         ARRAY_SIZE(desc->CompatibleID) +
  2962                         ARRAY_SIZE(desc->SubCompatibleID));
  2963                  length = sizeof(*desc);
  2964          }
  2965                  break;
  2966          case FFS_OS_DESC_EXT_PROP: {
  2967                  struct usb_ext_prop_desc *desc = data;
  2968                  struct usb_os_desc_table *t;
  2969                  struct usb_os_desc_ext_prop *ext_prop;
  2970                  char *ext_prop_name;
  2971                  char *ext_prop_data;
  2972  
  2973                  t = &func->function.os_desc_table[h->interface];
  2974                  t->if_id = func->interfaces_nums[h->interface];
  2975  
  2976                  ext_prop = func->ffs->ms_os_descs_ext_prop_avail;
  2977                  func->ffs->ms_os_descs_ext_prop_avail += sizeof(*ext_prop);
  2978  
  2979                  ext_prop->type = le32_to_cpu(desc->dwPropertyDataType);
  2980                  ext_prop->name_len = le16_to_cpu(desc->wPropertyNameLength);
  2981                  ext_prop->data_len = le32_to_cpu(*(__le32 *)
  2982                          usb_ext_prop_data_len_ptr(data, ext_prop->name_len));

Smatch is very suspicious of "ext_prop->data_len".

  2983                  length = ext_prop->name_len + ext_prop->data_len + 14;
  2984  
  2985                  ext_prop_name = func->ffs->ms_os_descs_ext_prop_name_avail;
  2986                  func->ffs->ms_os_descs_ext_prop_name_avail +=
  2987                          ext_prop->name_len;
  2988  
  2989                  ext_prop_data = func->ffs->ms_os_descs_ext_prop_data_avail;
  2990                  func->ffs->ms_os_descs_ext_prop_data_avail +=
  2991                          ext_prop->data_len;
  2992                  memcpy(ext_prop_data,
  2993                         usb_ext_prop_data_ptr(data, ext_prop->name_len),
  2994                         ext_prop->data_len);
                               ^^^^^^^^^^^^^^^^^^
so it complians that this memcpy() can overflow.  That seems like maybe
a real issue?

  2995                  /* unicode data reported to the host as "WCHAR"s */
  2996                  switch (ext_prop->type) {
  2997                  case USB_EXT_PROP_UNICODE:
  2998                  case USB_EXT_PROP_UNICODE_ENV:
  2999                  case USB_EXT_PROP_UNICODE_LINK:
  3000                  case USB_EXT_PROP_UNICODE_MULTI:
  3001                          ext_prop->data_len *= 2;
  3002                          break;
  3003                  }
  3004                  ext_prop->data = ext_prop_data;

regards,
dan carpenter