Re: [PATCH 1/1] usb: gadget: f_fs: Fix NULL pointer dereference in FUNCTIONFS_ENDPOINT_DESC

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Thu, Sep 17, 2026 at 09:53:37PM +0800, zjamg wrote:
> When user space sets up FunctionFS with only full-speed descriptors
> (e.g., flags = FUNCTIONFS_HAS_FS_DESC) and the gadget operates at a
> higher speed (such as USB_SPEED_HIGH or USB_SPEED_SUPER),
> config_ep_by_speed() detects that the function lacks descriptors for
> the current speed, logs a warning, and falls back to full-speed
> descriptors. The endpoint is then successfully enabled via
> usb_ep_enable(), and epfile->ep becomes valid.
> 
> However, when user space subsequently issues the FUNCTIONFS_ENDPOINT_DESC
> ioctl to query the endpoint descriptor, ffs_epfile_ioctl() selects the
> descriptor index solely based on gadget->speed:
> 
> 	switch (epfile->ffs->gadget->speed) {
> 	case USB_SPEED_SUPER:
> 	case USB_SPEED_SUPER_PLUS:
> 		desc_idx = 2;
> 		break;
> 	case USB_SPEED_HIGH:
> 		desc_idx = 1;
> 		break;
> 	default:
> 		desc_idx = 0;
> 	}
> 	desc = epfile->ep->descs[desc_idx];
> 	memcpy(&desc1, desc, desc->bLength);
> 
> Because user space only supplied full-speed descriptors,
> epfile->ep->descs[1] is NULL. Dereferencing desc->bLength triggers an
> immediate kernel NULL pointer dereference panic.
> 
> Fix this by falling back through lower speed descriptors if the current
> speed descriptor was not supplied, matching the fallback logic in
> config_ep_by_speed() and historical f_fs behavior. If still missing,
> fall back to epfile->ep->ep->desc (the active descriptor), and return
> -EINVAL safely if no valid descriptor is found. In addition, mark desc
> as const to match struct usb_ep::desc and avoid discarding qualifiers.
> 
> Fixes: c559a3534109 ("usb: gadget: f_fs: add ioctl returning ep descriptor")
> Cc: stable@vger.kernel.org
> Signed-off-by: zjamg <ndaugoing@gmail.com>
> ---
>  drivers/usb/gadget/function/f_fs.c | 15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
> 

Hi,

This is the friendly patch-bot of Greg Kroah-Hartman.  You have sent him
a patch that has triggered this response.  He used to manually respond
to these common problems, but in order to save his sanity (he kept
writing the same thing over and over, yet to different people), I was
created.  Hopefully you will not take offence and will fix the problem
in your patch and resubmit it so that it can be accepted into the Linux
kernel tree.

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