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Date: Mon, 29 Apr 2024 12:56:54 -0700
From: Kees Cook <keescook@chromium.org>
To: "Gustavo A. R. Silva" <gustavo@embeddedor.com>
Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>,
	Marcel Holtmann <marcel@holtmann.org>,
	Johan Hedberg <johan.hedberg@gmail.com>,
	Luiz Augusto von Dentz <luiz.dentz@gmail.com>,
	"David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	linux-bluetooth@vger.kernel.org, netdev@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: Re: [PATCH v2][next] Bluetooth: hci_conn, hci_sync: Use
 __counted_by() in multiple structs and avoid -Wfamnae warnings
Message-ID: <202404291253.106D020@keescook>
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 <202404291110.6159F7EA5@keescook>
 <b09450f9-c42f-41f8-a2f6-eea3515eaa2f@embeddedor.com>
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In-Reply-To: <b09450f9-c42f-41f8-a2f6-eea3515eaa2f@embeddedor.com>

On Mon, Apr 29, 2024 at 01:50:46PM -0600, Gustavo A. R. Silva wrote:
> 
> > > diff --git a/include/net/bluetooth/hci.h b/include/net/bluetooth/hci.h
> > > index fe23e862921d..c4c6b8810701 100644
> > > --- a/include/net/bluetooth/hci.h
> > > +++ b/include/net/bluetooth/hci.h
> > > @@ -2026,7 +2026,7 @@ struct hci_cp_le_set_ext_adv_data {
> > >   	__u8  operation;
> > >   	__u8  frag_pref;
> > >   	__u8  length;
> > > -	__u8  data[];
> > > +	__u8  data[] __counted_by(length);
> > >   } __packed;
> > 
> > I noticed some of the other structs here aren't flexible arrays, so it
> > made me go take a look at these ones. I see that the only user of struct
> > hci_cp_le_set_ext_adv_data uses a fixed-size array:
> > 
> >          struct {
> >                  struct hci_cp_le_set_ext_adv_data cp;
> >                  u8 data[HCI_MAX_EXT_AD_LENGTH];
> >          } pdu;
> > 
> > Let's just change this from a flex array to a fixed-size array?
> 
> mmh... not sure about this. It would basically mean reverting this commit:
> 
> c9ed0a707730 ("Bluetooth: Fix Set Extended (Scan Response) Data")

That change doesn't seem to need to make them flex arrays, though --
there's no savings at all (the same amount is stack allocated).

Anyway, not a big deal, I guess. It's an improvement to be using
__counted_by, so good! :)

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook