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From:   "Michael Kelley (LINUX)" <mikelley@microsoft.com>
To:     Arnd Bergmann <arnd@kernel.org>, Jiri Kosina <jikos@kernel.org>,
        Benjamin Tissoires <benjamin.tissoires@redhat.com>
CC:     Arnd Bergmann <arnd@arndb.de>, KY Srinivasan <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Wei Liu <wei.liu@kernel.org>, Dexuan Cui <decui@microsoft.com>,
        Paulo Miguel Almeida <paulo.miguel.almeida.rodenas@gmail.com>,
        Dawei Li <set_pte_at@outlook.com>,
        Yang Yingliang <yangyingliang@huawei.com>,
        =?iso-8859-1?Q?Thomas_Wei=DFschuh?= <linux@weissschuh.net>,
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        "linux-input@vger.kernel.org" <linux-input@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH] HID: hyperv: avoid struct memcpy overrun warning
Thread-Topic: [PATCH] HID: hyperv: avoid struct memcpy overrun warning
Thread-Index: AQHZr0llfkBz0jWXH027nvPaFIvXdK+v9I4w
Date:   Sat, 8 Jul 2023 14:37:28 +0000
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From: Arnd Bergmann <arnd@kernel.org> Sent: Wednesday, July 5, 2023 7:02 AM
>=20
> A previous patch addressed the fortified memcpy warning for most
> builds, but I still see this one with gcc-9:
>=20
> 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_fi=
eld' declared with
> attribute warning: detected write beyond size of field (1st parameter); m=
aybe use
> struct_group()? [-Werror=3Dattribute-warning]
>   583 |    __write_overflow_field(p_size_field, size);
>       |    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>=20
> 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.
>=20
> Fixes: 542f25a944715 ("HID: hyperv: Replace one-element array with flexib=
le-array member")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  drivers/hid/hid-hyperv.c | 10 ++++------
>  1 file changed, 4 insertions(+), 6 deletions(-)
>=20
> 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 *d=
evice,
>=20
>  	switch (hid_msg_hdr->type) {
>  	case SYNTH_HID_PROTOCOL_RESPONSE:
> +		len =3D 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;
> -		}
>=20
> -		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;
>=20
> --
> 2.39.2

Reviewed-by: Michael Kelley <mikelley@microsoft.com>