iwlwifi may wrongly cast a iwl_cfg_trans_params to iwl_cfg

[You-Sheng Yang <vicamo.yang@canonical.com>]

Hi,

With an Intel AX201 Wi-Fi [8086:43f0] subsystem [1a56:1652] pcie card,
device fails to load firmware with following error messages:

  Intel(R) Wireless WiFi driver for Linux
  iwlwifi 0000:00:14.3: enabling device (0000 -> 0002)
  iwlwifi 0000:00:14.3: Direct firmware load for (efault)128.ucode
failed with error -2
  iwlwifi 0000:00:14.3: Direct firmware load for (efault)127.ucode
failed with error -2
  ...
  iwlwifi 0000:00:14.3: Direct firmware load for (efault)0.ucode failed
with error -2
  iwlwifi 0000:00:14.3: no suitable firmware found!
  iwlwifi 0000:00:14.3: minimum version required: (efault)0
  iwlwifi 0000:00:14.3: maximum version supported: (efault)128

This is also reported on some public forums:

*
https://askubuntu.com/questions/1297311/ubuntu-20-04-wireless-not-working-for-intel-ax1650i-lenovo-thinkpad
*
https://www.reddit.com/r/pop_os/comments/jxmnre/wifi_and_bluetooth_issues_in_2010/

In drivers/net/wireless/intel/iwlwifi/pcie/drv.c:

  static const struct pci_device_id iwl_hw_card_ids[] = {
    {IWL_PCI_DEVICE(0x4232, 0x1201, iwl5100_agn_cfg)},
    ...
    {IWL_PCI_DEVICE(0x43F0, PCI_ANY_ID, iwl_qu_long_latency_trans_cfg)},
    ...
  };

The third argument to IWL_PCI_DEVICE macro will be assigned to
driver_data field of struct pci_device_id. However, iwl5100_agn_cfg has
type struct iwl_cfg, and yet iwl_qu_long_latency_trans_cfg is typed
struct iwl_cfg_trans_params.

  struct iwl_cfg_trans_params {
    ...
  };

  struct iwl_cfg {
    struct iwl_cfg_trans_params trans;
    const char *name;
    const char *fw_name_pre;
    ...
  };

It's fine to cast a pointer to struct iwl_cfg, but it's not always valid
to cast a struct iwl_cfg_trans_params to struct iwl_cfg.

In function iwl_pci_probe, it tries to find an alternative cfg by
iterating throughout iwl_dev_info_table, but in our case, [8086:43f0]
subsystem [1a56:1652], there will be no match in all of the candidates,
and iwl_qu_long_latency_trans_cfg will be assigned as the ultimate
struct iwl_cfg, which will be certainly wrong when you're trying to
dereference anything beyond sizeof(struct iwl_cfg_trans_params), e.g.
cfg->fw_name_pre.

In this case, ((struct
iwl_cfg_trans_params*)&iwl_qu_long_latency_trans_cfg)->name will be "'",
and ((struct
iwl_cfg_trans_params*)&iwl_qu_long_latency_trans_cfg)->fw_name_pre gives
"(efault)", pure garbage data.

So is there something missed in the iwl_dev_info_table, or better, just
find another solid safe way to handle such trans/cfg mix?

Regards,
You-Sheng Yang