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Date: Mon, 9 Oct 2023 09:56:11 -0700
From: Kees Cook <keescook@...omium.org>
To: Ping-Ke Shih <pkshih@...ltek.com>
Cc: "kvalo@...nel.org" <kvalo@...nel.org>,
	"llvm@...ts.linux.dev" <llvm@...ts.linux.dev>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
	"linux-hardening@...r.kernel.org" <linux-hardening@...r.kernel.org>,
	"trix@...hat.com" <trix@...hat.com>,
	"nathan@...nel.org" <nathan@...nel.org>,
	"ndesaulniers@...gle.com" <ndesaulniers@...gle.com>,
	"gustavoars@...nel.org" <gustavoars@...nel.org>
Subject: Re: [PATCH] wifi: rtw89: coex: Annotate struct
 rtw89_btc_btf_set_slot_table with __counted_by

On Sat, Oct 07, 2023 at 01:20:43AM +0000, Ping-Ke Shih wrote:
> On Fri, 2023-10-06 at 13:17 -0700, Kees Cook wrote:
> > 
> > Prepare for the coming implementation by GCC and Clang of the __counted_by
> > attribute. Flexible array members annotated with __counted_by can have
> > their accesses bounds-checked at run-time via CONFIG_UBSAN_BOUNDS (for
> > array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
> > functions).
> > 
> > As found with Coccinelle[1], add __counted_by for struct
> > rtw89_btc_btf_set_slot_table.
> > 
> > Cc: Ping-Ke Shih <pkshih@...ltek.com>
> > Cc: Kalle Valo <kvalo@...nel.org>
> > Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>
> > Cc: linux-wireless@...r.kernel.org
> > Cc: linux-hardening@...r.kernel.org
> > Link: https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci [1]
> > Signed-off-by: Kees Cook <keescook@...omium.org>
> > ---
> >  drivers/net/wireless/realtek/rtw89/coex.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/net/wireless/realtek/rtw89/coex.c b/drivers/net/wireless/realtek/rtw89/coex.c
> > index 4ba8b3df70ae..d66a1152c3f5 100644
> > --- a/drivers/net/wireless/realtek/rtw89/coex.c
> > +++ b/drivers/net/wireless/realtek/rtw89/coex.c
> > @@ -237,7 +237,7 @@ struct rtw89_btc_btf_set_report {
> >  struct rtw89_btc_btf_set_slot_table {
> >         u8 fver;
> >         u8 tbl_num;
> > -       u8 buf[];
> > +       u8 buf[] __counted_by(tbl_num);
> 
> This struct isn't defined properly. It should be 
> 
> struct rtw89_btc_btf_set_slot_table {
> 	u8 fver;
> 	u8 tbl_num;
> 	struct rtw89_btc_fbtc_slot tbl[] __counted_by(tbl_num);
> } __packed;
> 
> And, we should modify rtw89_btc_fw_set_slots() as well. 
> 
> Another struct 'rtw89_btc_btf_set_mon_reg' has similar problem.
> 
> So, NACK this patch. I will prepare one or two patches for them next week. 

Ah-ha; thank you!

> By the way, I have question about __counted_by(). Can I apply it to little/big-
> endian 'num'? Like
> 
> struct foo {
> 	...
> 	__le32 num;
> 	__le32 data[] __counted_by(num);
> }

Unfortunately not yet. I hope to see it extended in the future to allow
for arbitrary expressions. For this first step, it only handles native
sizes.

-- 
Kees Cook

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