Re: [PATCH] usb: ehci-fsl: Fix use of private data to avoid -Wflex-array-member-not-at-end warning

[Kees Cook <kees@kernel.org>]

On Thu, Mar 27, 2025 at 03:31:15PM -0400, Alan Stern wrote:
> In the course of fixing up the usages of flexible arrays, Gustavo
> submitted a patch updating the ehci-fsl driver.  However, the patch
> was wrong because the driver was using the .priv member of the
> ehci_hcd structure incorrectly.  The private data is not supposed to
> be a wrapper containing the ehci_hcd structure; it is supposed to be a
> sub-structure stored in the .priv member.
> 
> Fix the problem by replacing the ehci_fsl structure with
> ehci_fsl_priv, containing only the private data, along with a suitable
> conversion macro for accessing it.  This removes the problem of having
> data follow a flexible array member.

Thanks for figuring out the right solution! :)

> 
> Reported-by: "Gustavo A. R. Silva" <gustavoars@kernel.org>
> Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
> Link: https://lore.kernel.org/linux-usb/Z-R9BcnSzrRv5FX_@kspp/

Reviewed-by: Kees Cook <kees@kernel.org>

-Kees

> 
> ---
> 
>  drivers/usb/host/ehci-fsl.c |   25 ++++++++-----------------
>  1 file changed, 8 insertions(+), 17 deletions(-)
> 
> Index: usb-devel/drivers/usb/host/ehci-fsl.c
> ===================================================================
> --- usb-devel.orig/drivers/usb/host/ehci-fsl.c
> +++ usb-devel/drivers/usb/host/ehci-fsl.c
> @@ -410,15 +410,13 @@ static int ehci_fsl_setup(struct usb_hcd
>  	return retval;
>  }
>  
> -struct ehci_fsl {
> -	struct ehci_hcd	ehci;
> -
> -#ifdef CONFIG_PM
> +struct ehci_fsl_priv {
>  	/* Saved USB PHY settings, need to restore after deep sleep. */
>  	u32 usb_ctrl;
> -#endif
>  };
>  
> +#define hcd_to_ehci_fsl_priv(h) ((struct ehci_fsl_priv *) hcd_to_ehci(h)->priv)
> +
>  #ifdef CONFIG_PM
>  
>  #ifdef CONFIG_PPC_MPC512x
> @@ -566,17 +564,10 @@ static inline int ehci_fsl_mpc512x_drv_r
>  }
>  #endif /* CONFIG_PPC_MPC512x */
>  
> -static struct ehci_fsl *hcd_to_ehci_fsl(struct usb_hcd *hcd)
> -{
> -	struct ehci_hcd *ehci = hcd_to_ehci(hcd);
> -
> -	return container_of(ehci, struct ehci_fsl, ehci);
> -}
> -
>  static int ehci_fsl_drv_suspend(struct device *dev)
>  {
>  	struct usb_hcd *hcd = dev_get_drvdata(dev);
> -	struct ehci_fsl *ehci_fsl = hcd_to_ehci_fsl(hcd);
> +	struct ehci_fsl_priv *priv = hcd_to_ehci_fsl_priv(hcd);
>  	void __iomem *non_ehci = hcd->regs;
>  
>  	if (of_device_is_compatible(dev->parent->of_node,
> @@ -589,14 +580,14 @@ static int ehci_fsl_drv_suspend(struct d
>  	if (!fsl_deep_sleep())
>  		return 0;
>  
> -	ehci_fsl->usb_ctrl = ioread32be(non_ehci + FSL_SOC_USB_CTRL);
> +	priv->usb_ctrl = ioread32be(non_ehci + FSL_SOC_USB_CTRL);
>  	return 0;
>  }
>  
>  static int ehci_fsl_drv_resume(struct device *dev)
>  {
>  	struct usb_hcd *hcd = dev_get_drvdata(dev);
> -	struct ehci_fsl *ehci_fsl = hcd_to_ehci_fsl(hcd);
> +	struct ehci_fsl_priv *priv = hcd_to_ehci_fsl_priv(hcd);
>  	struct ehci_hcd *ehci = hcd_to_ehci(hcd);
>  	void __iomem *non_ehci = hcd->regs;
>  
> @@ -612,7 +603,7 @@ static int ehci_fsl_drv_resume(struct de
>  	usb_root_hub_lost_power(hcd->self.root_hub);
>  
>  	/* Restore USB PHY settings and enable the controller. */
> -	iowrite32be(ehci_fsl->usb_ctrl, non_ehci + FSL_SOC_USB_CTRL);
> +	iowrite32be(priv->usb_ctrl, non_ehci + FSL_SOC_USB_CTRL);
>  
>  	ehci_reset(ehci);
>  	ehci_fsl_reinit(ehci);
> @@ -671,7 +662,7 @@ static int ehci_start_port_reset(struct
>  #endif /* CONFIG_USB_OTG */
>  
>  static const struct ehci_driver_overrides ehci_fsl_overrides __initconst = {
> -	.extra_priv_size = sizeof(struct ehci_fsl),
> +	.extra_priv_size = sizeof(struct ehci_fsl_priv),
>  	.reset = ehci_fsl_setup,
>  };
>  

-- 
Kees Cook