linux-hardening - Re: [PATCH v3] batman-adv: Add flex array to struct batadv_tvlv_tt

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Date: Sat, 4 May 2024 19:08:39 +0200
From: Erick Archer <erick.archer@...look.com>
To: Sven Eckelmann <sven@...fation.org>
Cc: Marek Lindner <mareklindner@...mailbox.ch>,
	Simon Wunderlich <sw@...onwunderlich.de>,
	Antonio Quartulli <a@...table.cc>,
	"David S.  Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Nathan Chancellor <nathan@...nel.org>,
	Nick Desaulniers <ndesaulniers@...gle.com>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	Kees Cook <keescook@...omium.org>,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>,
	Erick Archer <erick.archer@...look.com>,
	b.a.t.m.a.n@...ts.open-mesh.org, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, linux-hardening@...r.kernel.org,
	llvm@...ts.linux.dev,
	Alexander Lobakin <aleksander.lobakin@...el.com>
Subject: Re: [PATCH v3] batman-adv: Add flex array to struct
 batadv_tvlv_tt_data

Hi Sven,

On Sat, May 04, 2024 at 11:35:38AM +0200, Sven Eckelmann wrote:
> On Wednesday, 1 May 2024 17:02:42 CEST Erick Archer wrote:
> > diff --git a/include/uapi/linux/batadv_packet.h b/include/uapi/linux/batadv_packet.h
> > index 6e25753015df..dfbe30536995 100644
> > --- a/include/uapi/linux/batadv_packet.h
> > +++ b/include/uapi/linux/batadv_packet.h
> [...]
> > +/**
> > + * struct batadv_tvlv_tt_data - tt data propagated through the tt tvlv container
> > + * @flags: translation table flags (see batadv_tt_data_flags)
> > + * @ttvn: translation table version number
> > + * @num_vlan: number of announced VLANs. In the TVLV this struct is followed by
> > + *  one batadv_tvlv_tt_vlan_data object per announced vlan
> > + * @vlan_data: array of batadv_tvlv_tt_vlan_data objects
> > + */
> > +struct batadv_tvlv_tt_data {
> > +       __u8   flags;
> > +       __u8   ttvn;
> > +       __be16 num_vlan;
> > +       struct batadv_tvlv_tt_vlan_data vlan_data[] __counted_by_be(num_vlan);
> > +};
> 
> Thanks for the updates. But I can't accept this at the moment because 
> __counted_by_be is used in an uapi header without it being defined
> include/uapi/linux/stddef.h (and this file is also not included in this 
> header).
> 
> See commit c8248faf3ca2 ("Compiler Attributes: counted_by: Adjust name and 
> identifier expansion") as an example for the similar __counted_by macro.

If I understand correctly, the following changes are also needed because
the annotated struct is defined in a "uapi" header. Sorry if it's a stupid
question, but I'm new to these topics.

diff --git a/include/uapi/linux/batadv_packet.h b/include/uapi/linux/batadv_packet.h
index 6e25753015df..41f39d7661c9 100644
--- a/include/uapi/linux/batadv_packet.h
+++ b/include/uapi/linux/batadv_packet.h
@@ -9,6 +9,7 @@

 #include <asm/byteorder.h>
 #include <linux/if_ether.h>
+#include <linux/stddef.h>
 #include <linux/types.h>

 /**
diff --git a/include/uapi/linux/stddef.h b/include/uapi/linux/stddef.h
index 2ec6f35cda32..58154117d9b0 100644
--- a/include/uapi/linux/stddef.h
+++ b/include/uapi/linux/stddef.h
@@ -55,4 +55,12 @@
 #define __counted_by(m)
 #endif

+#ifndef __counted_by_le
+#define __counted_by_le(m)
+#endif
+
+#ifndef __counted_by_be
+#define __counted_by_be(m)
+#endif
+
 #endif /* _UAPI_LINUX_STDDEF_H */

If this is the right path, can these changes be merged into a
single patch or is it better to add a previous patch to define
__counted_by{le,be}?

Regards,
Erick

> Kind regards,
> 	Sven