linux-hardening - Re: [PATCH 2/5] treewide: Replace open-coded flex arrays in unions

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Message-ID: <202108181448.9C13CE9@keescook>
Date:   Wed, 18 Aug 2021 14:51:06 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Marc Kleine-Budde <mkl@...gutronix.de>
Cc:     linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Ayush Sawal <ayush.sawal@...lsio.com>,
        Vinay Kumar Yadav <vinay.yadav@...lsio.com>,
        Rohit Maheshwari <rohitm@...lsio.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        Kalle Valo <kvalo@...eaurora.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Stanislaw Gruszka <stf_xl@...pl>,
        Luca Coelho <luciano.coelho@...el.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Johannes Berg <johannes.berg@...el.com>,
        Mordechay Goodstein <mordechay.goodstein@...el.com>,
        Lee Jones <lee.jones@...aro.org>,
        Wolfgang Grandegger <wg@...ndegger.com>,
        Arunachalam Santhanam <arunachalam.santhanam@...bosch.com>,
        Vincent Mailhol <mailhol.vincent@...adoo.fr>,
        Mikulas Patocka <mikulas@...ax.karlin.mff.cuni.cz>,
        linux-crypto@...r.kernel.org, ath10k@...ts.infradead.org,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-scsi@...r.kernel.org, linux-can@...r.kernel.org,
        bpf@...r.kernel.org, clang-built-linux@...glegroups.com,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH 2/5] treewide: Replace open-coded flex arrays in unions

On Wed, Aug 18, 2021 at 11:56:35AM +0200, Marc Kleine-Budde wrote:
> On 18.08.2021 01:11:15, Kees Cook wrote:
> > diff --git a/drivers/net/can/usb/etas_es58x/es581_4.h b/drivers/net/can/usb/etas_es58x/es581_4.h
> > index 4bc60a6df697..8657145dc2a9 100644
> > --- a/drivers/net/can/usb/etas_es58x/es581_4.h
> > +++ b/drivers/net/can/usb/etas_es58x/es581_4.h
> > @@ -192,7 +192,7 @@ struct es581_4_urb_cmd {
> >  		struct es581_4_rx_cmd_ret rx_cmd_ret;
> >  		__le64 timestamp;
> >  		u8 rx_cmd_ret_u8;
> > -		u8 raw_msg[0];
> > +		flex_array(u8 raw_msg);
> >  	} __packed;
> >  
> >  	__le16 reserved_for_crc16_do_not_use;
> > diff --git a/drivers/net/can/usb/etas_es58x/es58x_fd.h b/drivers/net/can/usb/etas_es58x/es58x_fd.h
> > index ee18a87e40c0..3053e0958132 100644
> > --- a/drivers/net/can/usb/etas_es58x/es58x_fd.h
> > +++ b/drivers/net/can/usb/etas_es58x/es58x_fd.h
> > @@ -228,7 +228,7 @@ struct es58x_fd_urb_cmd {
> >  		struct es58x_fd_tx_ack_msg tx_ack_msg;
> >  		__le64 timestamp;
> >  		__le32 rx_cmd_ret_le32;
> > -		u8 raw_msg[0];
> > +		flex_array(u8 raw_msg[]);
> >  	} __packed;
> 
> This doesn't look consistent, what's preferred?
> 
> u8 raw_msg[0];  -> flex_array(u8 raw_msg);
>  - or-
>                 -> flex_array(u8 raw_msg[]);

Eek, thanks for catching that. And this helps me realize that having
"flex_array" and "[]" is redundant, and the above typo would have been
caught. I will fix this for v2.

Thanks!

-Kees

-- 
Kees Cook