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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id y13sm5730422pfq.147.2021.08.18.02.03.17 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 18 Aug 2021 02:03:17 -0700 (PDT) Date: Wed, 18 Aug 2021 02:03:16 -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: <202108180159.5C1CEE70F@keescook> References: <20210818034010.800652-1-keescook@chromium.org> <202108172320.1540EC10C@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 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. :) -- Kees Cook