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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id w9sm872502pja.16.2021.08.18.17.02.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 18 Aug 2021 17:02:11 -0700 (PDT) Date: Wed, 18 Aug 2021 17:02:10 -0700 From: Kees Cook To: Vincent MAILHOL Cc: Wolfgang Grandegger , Marc Kleine-Budde , "David S. Miller" , Jakub Kicinski , Arunachalam Santhanam , linux-can , netdev , open list , linux-hardening@vger.kernel.org Subject: Re: [PATCH] can: etas_es58x: Replace 0-element raw_msg array Message-ID: <202108181659.3DE5E5451@keescook> References: <20210818034010.800652-1-keescook@chromium.org> <202108172320.1540EC10C@keescook> <202108180159.5C1CEE70F@keescook> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-can@vger.kernel.org On Wed, Aug 18, 2021 at 06:33:39PM +0900, Vincent MAILHOL wrote: > On Wed. 18 Aug 2021 at 18:03, Kees Cook wrote: > > On Wed, Aug 18, 2021 at 04:55:20PM +0900, Vincent MAILHOL wrote: > > > At the end, the only goal of raw_msg[] is to have a tag pointing > > > to the beginning of the union. It would be virtually identical to > > > something like: > > > | u8 raw_msg[]; > > > | union { > > > | /* ... */ > > > | } __packed ; > > > > > > I had a look at your work and especially at your struct_group() macro. > > > Do you think it would make sense to introduce a union_group()? > > > > > > Result would look like: > > > > > > | union_group_attr(urb_msg, __packed, /* raw_msg renamed to urb_msg */ > > > | struct es58x_fd_tx_conf_msg tx_conf_msg; > > > | u8 tx_can_msg_buf[ES58X_FD_TX_BULK_MAX * ES58X_FD_CANFD_TX_LEN]; > > > | u8 rx_can_msg_buf[ES58X_FD_RX_BULK_MAX * ES58X_FD_CANFD_RX_LEN]; > > > | struct es58x_fd_echo_msg echo_msg[ES58X_FD_ECHO_BULK_MAX]; > > > | struct es58x_fd_rx_event_msg rx_event_msg; > > > | struct es58x_fd_tx_ack_msg tx_ack_msg; > > > | __le64 timestamp; > > > | __le32 rx_cmd_ret_le32; > > > | ); > > > > > > And I can then use urb_msg in place of the old raw_msg (might > > > need a bit of rework here and there but I can take care of it). > > > > > > This is the most pretty way I can think of to remove this zero length array. > > > Keeping the raw_msg[] but with another size seems odd to me. > > > > > > Or maybe I would be the only one using this feature in the full > > > tree? In that case, maybe it would make sense to keep the > > > union_group_attr() macro local to the etas_es58x driver? > > > > I actually ended up with something close to this idea, but more > > generalized for other cases in the kernel. There was a sane way to > > include a "real" flexible array in a union (or alone in a struct), so > > I've proposed this flex_array() helper: > > https://lore.kernel.org/lkml/20210818081118.1667663-2-keescook@chromium.org/ > > > > and then it's just a drop-in replacement for all the places that need > > this fixed, including etas_es58x: > > https://lore.kernel.org/lkml/20210818081118.1667663-3-keescook@chromium.org/#Z30drivers:net:can:usb:etas_es58x:es581_4.h > > > > Hopefully this will work out; I think it's as clean as we can get for > > now. :) > > The __flex_array itself is a nasty hack :D Indeed. ;) > but the rest is clean. Thanks! > Is this compliant to the C standard? Well, I guess that as long > as both GCC and LLVM supports it, it is safe to add it to the > kernel. The kernel already uses a bunch of compiler extensions, none of which were legal under the C standard to begin with. :) So, really, this is about normalizing what we're already doing and finding a single hack that helps the code base for readability and robustness. > I like the final result. I will do a bit more testing and give my > acknowledgement if everything goes well. Great; thank you! -- Kees Cook