Re: [PATCH] usb: ch9: Replace bmSublinkSpeedAttr 1-element array with flexible array

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

On Thu, Jun 29, 2023 at 12:09:00PM -0700, Kees Cook wrote:
> Since commit df8fc4e934c1 ("kbuild: Enable -fstrict-flex-arrays=3"),
> UBSAN_BOUNDS no longer pretends 1-element arrays are unbounded. Walking
> bmSublinkSpeedAttr will trigger a warning, so make it a proper flexible
> array. Add a union to keep the struct size identical for userspace in
> case anything was depending on the old size.
> 
> False positive warning was:
> 
> UBSAN: array-index-out-of-bounds in drivers/usb/host/xhci-hub.c:231:31 index 1 is out of range for type '__le32 [1]'
> 
> for this line of code:
> 
> 	ssp_cap->bmSublinkSpeedAttr[offset++] = cpu_to_le32(attr);
> 
> Reported-by: Borislav Petkov <bp@alien8.de>
> Closes: https://lore.kernel.org/lkml/2023062945-fencing-pebble-0411@gregkh/
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
>  include/uapi/linux/usb/ch9.h | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)

Thanks for the quick response, I'll queue it up after 6.5-rc1 is out.

Boris, can you test if this fixes the issue you see or not?

greg k-h