linux-hardening - Re: [PATCH] greybus: audio: apbridgea: Remove flexible array from struct audio_apbridgea

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Date: Tue, 27 Feb 2024 08:25:11 -0700
From: Mark Greer <mgreer@...malcreek.com>
To: Alex Elder <elder@...e.org>
Cc: Erick Archer <erick.archer@....com>,
	Vaibhav Agarwal <vaibhav.sr@...il.com>,
	Mark Greer <mgreer@...malcreek.com>,
	Johan Hovold <johan@...nel.org>, Alex Elder <elder@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>,
	Kees Cook <keescook@...omium.org>, greybus-dev@...ts.linaro.org,
	linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: Re: [PATCH] greybus: audio: apbridgea: Remove flexible array from
 struct audio_apbridgea_hdr

On Sat, Feb 17, 2024 at 03:18:59PM -0600, Alex Elder wrote:
> On 2/17/24 9:47 AM, Erick Archer wrote:
> > When a struct containing a flexible array is included in another struct,
> > and there is a member after the struct-with-flex-array, there is a
> > possibility of memory overlap. These cases must be audited [1]. See:
> > 
> > struct inner {
> > 	...
> > 	int flex[];
> > };
> > 
> > struct outer {
> > 	...
> > 	struct inner header;
> > 	int overlap;
> > 	...
> > };
> > 
> > This is the scenario for the "struct audio_apbridgea_hdr" structure
> > that is included in the following "struct audio_apbridgea_*_request"
> > structures:
> 
> Yeah this was not a very good way to define these header
> structures, but I'm glad to hear the flexible array at the
> end was never used.  I don't know why it was there; maybe
> it's an artifact from some other information that got removed.
> 
> If the code compiles with your change, it ought to be fine.
> (It compiles for me.)
> 
> It would be good for Vaibhav or Mark to comment though, maybe
> they can provide some context.

Sorry for the delay guys.

The way this was done comes from associated firmware that ran on the
APBridge. This goes back a while but I think the packet headers may have
been in flux at the time and this was a convenient way to change all of
the packets if & when it changed.  Anyway, it doesn't seem so convenient
now. :)

So, yeah, getting rid of it sounds like a good thing to do to me.

> I'd like to hear from these others, but otherwise this change
> looks good to me.
> 
> Reviewed-by: Alex Elder <elder@...aro.org>


> > diff --git a/drivers/staging/greybus/audio_apbridgea.h b/drivers/staging/greybus/audio_apbridgea.h
> > index efec0f815efd..ab707d310129 100644
> > --- a/drivers/staging/greybus/audio_apbridgea.h
> > +++ b/drivers/staging/greybus/audio_apbridgea.h
> > @@ -65,7 +65,6 @@
> >   struct audio_apbridgea_hdr {
> >   	__u8	type;
> >   	__le16	i2s_port;
> > -	__u8	data[];
> >   } __packed;
> > 
> >   struct audio_apbridgea_set_config_request {
> > --
> > 2.25.1

Acked-by: Mark Greer <mgreer@...malcreek.com>