linux-hardening - Re: [PATCH] [next] HID: hyperv: Replace one-element array with flexible-array member

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Date:   Mon, 17 Oct 2022 22:30:33 +1300
From:   Paulo Miguel Almeida <paulo.miguel.almeida.rodenas@...il.com>
To:     Benjamin Tissoires <benjamin.tissoires@...hat.com>
Cc:     "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
        Jiri Kosina <jikos@...nel.org>, linux-hyperv@...r.kernel.org,
        linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH] [next] HID: hyperv: Replace one-element array with
 flexible-array member

On Mon, Oct 17, 2022 at 10:30:54AM +0200, Benjamin Tissoires wrote:
> On Mon, Oct 17, 2022 at 9:51 AM Paulo Miguel Almeida
> <paulo.miguel.almeida.rodenas@...il.com> 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@...il.com>
> > ---
> 
> FWIW, this is
> Reviewed-by: Benjamin Tissoires <benjamin.tissoires@...hat.com>
> 
Thanks for reviewing this patch :-)

> > +++ 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 */
> >  };
> 
> IMO that struct has no real use. We just use it in
> mousevsc_on_receive() to dereference the first field only, the header.
> So how about we have a followup cleanup patch that just removes it and
> in mousevsc_on_receive() we convert those usages directly to struct
> synthhid_msg_hdr?
> 
> Cheers,
> Benjamin

I'm happy to send a followup cleanup patch for that.

Paulo A.