From: Arnd Bergmann <arnd@xxxxxxxxxx> Sent: Wednesday, July 5, 2023 7:02 AM
>
> A previous patch addressed the fortified memcpy warning for most
> builds, but I still see this one with gcc-9:
>
> In file included from include/linux/string.h:254,
> from drivers/hid/hid-hyperv.c:8:
> In function 'fortify_memcpy_chk',
> inlined from 'mousevsc_on_receive' at drivers/hid/hid-hyperv.c:272:3:
> include/linux/fortify-string.h:583:4: error: call to '__write_overflow_field' declared with
> attribute warning: detected write beyond size of field (1st parameter); maybe use
> struct_group()? [-Werror=attribute-warning]
> 583 | __write_overflow_field(p_size_field, size);
> | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> My guess is that the WARN_ON() itself is what confuses gcc, so it no
> longer sees that there is a correct range check. Rework the code in a
> way that helps readability and avoids the warning.
>
> Fixes: 542f25a944715 ("HID: hyperv: Replace one-element array with flexible-array member")
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> ---
> drivers/hid/hid-hyperv.c | 10 ++++------
> 1 file changed, 4 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/hid/hid-hyperv.c b/drivers/hid/hid-hyperv.c
> index 49d4a26895e76..f33485d83d24f 100644
> --- a/drivers/hid/hid-hyperv.c
> +++ b/drivers/hid/hid-hyperv.c
> @@ -258,19 +258,17 @@ static void mousevsc_on_receive(struct hv_device *device,
>
> switch (hid_msg_hdr->type) {
> case SYNTH_HID_PROTOCOL_RESPONSE:
> + len = struct_size(pipe_msg, data, pipe_msg->size);
> +
> /*
> * While it will be impossible for us to protect against
> * malicious/buggy hypervisor/host, add a check here to
> * ensure we don't corrupt memory.
> */
> - if (struct_size(pipe_msg, data, pipe_msg->size)
> - > sizeof(struct mousevsc_prt_msg)) {
> - WARN_ON(1);
> + if (WARN_ON(len > sizeof(struct mousevsc_prt_msg)))
> break;
> - }
>
> - memcpy(&input_dev->protocol_resp, pipe_msg,
> - struct_size(pipe_msg, data, pipe_msg->size));
> + memcpy(&input_dev->protocol_resp, pipe_msg, len);
> complete(&input_dev->wait_event);
> break;
>
> --
> 2.39.2
Reviewed-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>
