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Date:   Tue, 18 Oct 2022 14:56:21 +0200 (CEST)
From:   Jiri Kosina <jikos@kernel.org>
To:     "Michael Kelley (LINUX)" <mikelley@microsoft.com>
cc:     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>,
        Benjamin Tissoires <benjamin.tissoires@redhat.com>,
        "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
        "linux-input@vger.kernel.org" <linux-input@vger.kernel.org>,
        "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
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On Mon, 17 Oct 2022, Michael Kelley (LINUX) wrote:

> > 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.
> > 
> > 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=3 [1].
> > 
> > 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=101836 [1]
> > 
> > Signed-off-by: Paulo Miguel Almeida <paulo.miguel.almeida.rodenas@gmail.com>
> > ---
> >  drivers/hid/hid-hyperv.c | 17 +++++++----------
> >  1 file changed, 7 insertions(+), 10 deletions(-)
> > 
> > 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 {
> > 
> >  struct synthhid_msg {
> >  	struct synthhid_msg_hdr header;
> > -	char data[1]; /* Enclosed message */
> > +	char data[]; /* Enclosed message */
> >  };
> > 
> >  union synthhid_version {
> > @@ -99,7 +99,7 @@ struct synthhid_device_info_ack {
> > 
> >  struct synthhid_input_report {
> >  	struct synthhid_msg_hdr header;
> > -	char buffer[1];
> > +	char buffer[];
> >  };
> > 
> >  #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[];
> >  };
> > 
> >  struct  mousevsc_prt_msg {
> > @@ -232,7 +232,7 @@ static void mousevsc_on_receive_device_info(struct
> > mousevsc_dev *input_device,
> > 
> >  	ret = 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 *device,
> >  		 * 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;
> >  		}
> > 
> >  		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;
> > 
> > @@ -359,8 +357,7 @@ static int mousevsc_connect_to_vsp(struct hv_device *device)
> >  	request->request.version_requested.version = SYNTHHID_INPUT_VERSION;
> > 
> >  	ret = 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>

Thanks, applied.

-- 
Jiri Kosina
SUSE Labs