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SubjectRe: [PATCH][next] usb: dwc2: Use flex_array_size() helper
Date
Hi,

Gustavo A. R. Silva wrote:
> Make use of the flex_array_size() helper to calculate the size of a
> flexible array member within an enclosing structure.
>
> This helper offers defense-in-depth against potential integer
> overflows, while at the same time makes it explicitly clear that
> we are dealing with a flexible array member.
>
> Link: https://urldefense.com/v3/__https://github.com/KSPP/linux/issues/160__;!!A4F2R9G_pg!L8p7TlfbH0sNpL9gtsVuWEZVnP8euMZtJKpc71sXxzEw4MAKWuQ28dJJc0cJTI3bWXLm$
> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
> ---
> drivers/usb/dwc2/hcd.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/usb/dwc2/hcd.c b/drivers/usb/dwc2/hcd.c
> index f63a27d11fac..2c21498662cd 100644
> --- a/drivers/usb/dwc2/hcd.c
> +++ b/drivers/usb/dwc2/hcd.c
> @@ -4054,8 +4054,9 @@ struct dwc2_tt *dwc2_host_get_tt_info(struct dwc2_hsotg *hsotg, void *context,
> * For single_tt we need one schedule. For multi_tt
> * we need one per port.
> */
> - bitmap_size = DWC2_ELEMENTS_PER_LS_BITMAP *
> - sizeof(dwc_tt->periodic_bitmaps[0]);
> + bitmap_size =
> + flex_array_size(dwc_tt, periodic_bitmaps,
> + DWC2_ELEMENTS_PER_LS_BITMAP);
> if (urb->dev->tt->multi)
> bitmap_size *= urb->dev->tt->hub->maxchild;
>

This doesn't look right even though the result will be the same. The
return value from flex_array_size() may not be the final array size as you
can see that bitmap_size gets updated again a couple lines down.

How about this instead:

diff --git a/drivers/usb/dwc2/hcd.c b/drivers/usb/dwc2/hcd.c
index f63a27d11fac..0936ff8b57db 100644
--- a/drivers/usb/dwc2/hcd.c
+++ b/drivers/usb/dwc2/hcd.c
@@ -4048,18 +4048,17 @@ struct dwc2_tt *dwc2_host_get_tt_info(struct dwc2_hsotg *hsotg, void *context,

dwc_tt = urb->dev->tt->hcpriv;
if (!dwc_tt) {
- size_t bitmap_size;
+ int count;

/*
* For single_tt we need one schedule. For multi_tt
* we need one per port.
*/
- bitmap_size = DWC2_ELEMENTS_PER_LS_BITMAP *
- sizeof(dwc_tt->periodic_bitmaps[0]);
+ count = DWC2_ELEMENTS_PER_LS_BITMAP;
if (urb->dev->tt->multi)
- bitmap_size *= urb->dev->tt->hub->maxchild;
+ count *= urb->dev->tt->hub->maxchild;

- dwc_tt = kzalloc(sizeof(*dwc_tt) + bitmap_size,
+ dwc_tt = kzalloc(struct_size(dwc_tt, periodic_bitmaps, count),
mem_flags);
if (!dwc_tt)
return NULL;

BR,
Thinh
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