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From:   "Michael Kelley (LINUX)" <mikelley@microsoft.com>
To:     Paulo Miguel Almeida <paulo.miguel.almeida.rodenas@gmail.com>,
        KY Srinivasan <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        Wei Liu <wei.liu@kernel.org>, Dexuan Cui <decui@microsoft.com>,
        Jiri Kosina <jikos@kernel.org>,
        Benjamin Tissoires <benjamin.tissoires@redhat.com>,
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CC:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-hardening@vger.kernel.org" <linux-hardening@vger.kernel.org>
Subject: RE: [PATCH] [next] HID: hyperv: Replace one-element array with
 flexible-array member
Thread-Topic: [PATCH] [next] HID: hyperv: Replace one-element array with
 flexible-array member
Thread-Index: AQHY4f1NVEkUfmHplUioVuVVmpSZoa4SsbJA
Date:   Mon, 17 Oct 2022 15:15:04 +0000
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From: Paulo Miguel Almeida <paulo.miguel.almeida.rodenas@gmail.com> Sent: M=
onday, October 17, 2022 12:51 AM
>=20
> One-element arrays are deprecated, and we are replacing them with
> flexible array members instead. So, replace one-element array with
> flexible-array member in structs synthhid_msg, synthhid_input_report,
> pipe_prt_msg and refactor the rest of the code accordingly.
>=20
> This helps with the ongoing efforts to tighten the FORTIFY_SOURCE
> routines on memcpy() and help us make progress towards globally
> enabling -fstrict-flex-arrays=3D3 [1].
>=20
> Link: https://github.com/KSPP/linux/issues/79
> Link: https://github.com/KSPP/linux/issues/210
> Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101836 [1]
>=20
> Signed-off-by: Paulo Miguel Almeida <paulo.miguel.almeida.rodenas@gmail.c=
om>
> ---
>  drivers/hid/hid-hyperv.c | 17 +++++++----------
>  1 file changed, 7 insertions(+), 10 deletions(-)
>=20
> diff --git a/drivers/hid/hid-hyperv.c b/drivers/hid/hid-hyperv.c
> index e0bc73124196..208cf8d981a5 100644
> --- a/drivers/hid/hid-hyperv.c
> +++ b/drivers/hid/hid-hyperv.c
> @@ -61,7 +61,7 @@ struct synthhid_msg_hdr {
>=20
>  struct synthhid_msg {
>  	struct synthhid_msg_hdr header;
> -	char data[1]; /* Enclosed message */
> +	char data[]; /* Enclosed message */
>  };
>=20
>  union synthhid_version {
> @@ -99,7 +99,7 @@ struct synthhid_device_info_ack {
>=20
>  struct synthhid_input_report {
>  	struct synthhid_msg_hdr header;
> -	char buffer[1];
> +	char buffer[];
>  };
>=20
>  #pragma pack(pop)
> @@ -118,7 +118,7 @@ enum pipe_prot_msg_type {
>  struct pipe_prt_msg {
>  	enum pipe_prot_msg_type type;
>  	u32 size;
> -	char data[1];
> +	char data[];
>  };
>=20
>  struct  mousevsc_prt_msg {
> @@ -232,7 +232,7 @@ static void mousevsc_on_receive_device_info(struct
> mousevsc_dev *input_device,
>=20
>  	ret =3D vmbus_sendpacket(input_device->device->channel,
>  			&ack,
> -			sizeof(struct pipe_prt_msg) - sizeof(unsigned char) +
> +			sizeof(struct pipe_prt_msg) +
>  			sizeof(struct synthhid_device_info_ack),
>  			(unsigned long)&ack,
>  			VM_PKT_DATA_INBAND,
> @@ -271,16 +271,14 @@ static void mousevsc_on_receive(struct hv_device *d=
evice,
>  		 * malicious/buggy hypervisor/host, add a check here to
>  		 * ensure we don't corrupt memory.
>  		 */
> -		if ((pipe_msg->size + sizeof(struct pipe_prt_msg)
> -			- sizeof(unsigned char))
> +		if (struct_size(pipe_msg, data, pipe_msg->size)
>  			> sizeof(struct mousevsc_prt_msg)) {
>  			WARN_ON(1);
>  			break;
>  		}
>=20
>  		memcpy(&input_dev->protocol_resp, pipe_msg,
> -		       pipe_msg->size + sizeof(struct pipe_prt_msg) -
> -		       sizeof(unsigned char));
> +				struct_size(pipe_msg, data, pipe_msg->size));
>  		complete(&input_dev->wait_event);
>  		break;
>=20
> @@ -359,8 +357,7 @@ static int mousevsc_connect_to_vsp(struct hv_device *=
device)
>  	request->request.version_requested.version =3D SYNTHHID_INPUT_VERSION;
>=20
>  	ret =3D vmbus_sendpacket(device->channel, request,
> -				sizeof(struct pipe_prt_msg) -
> -				sizeof(unsigned char) +
> +				sizeof(struct pipe_prt_msg) +
>  				sizeof(struct synthhid_protocol_request),
>  				(unsigned long)request,
>  				VM_PKT_DATA_INBAND,
> --
> 2.37.3

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