| Message ID | 20210818034010.800652-1-keescook@chromium.org |
|---|---|
| State | New |
| Headers | show |
| Series | can: etas_es58x: Replace 0-element raw_msg array | expand |
On Wed, Aug 18, 2021 at 06:33:39PM +0900, Vincent MAILHOL wrote: > On Wed. 18 Aug 2021 at 18:03, Kees Cook <keescook@chromium.org> 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!
diff --git a/drivers/net/can/usb/etas_es58x/es581_4.h b/drivers/net/can/usb/etas_es58x/es581_4.h index 4bc60a6df697..af38c4938859 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]; + u8 raw_msg[USHRT_MAX]; } __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..e0319b8358ef 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]; + u8 raw_msg[USHRT_MAX]; } __packed; __le16 reserved_for_crc16_do_not_use;
While raw_msg isn't a fixed size, it does have a maximum size. Adjust the struct to represent this and avoid the following warning when building with -Wzero-length-bounds: drivers/net/can/usb/etas_es58x/es58x_fd.c: In function 'es58x_fd_tx_can_msg': drivers/net/can/usb/etas_es58x/es58x_fd.c:360:35: warning: array subscript 65535 is outside the bounds of an interior zero-length array 'u8[0]' {aka 'unsigned char[]'} [-Wzero-length-bounds] 360 | tx_can_msg = (typeof(tx_can_msg))&es58x_fd_urb_cmd->raw_msg[msg_len]; | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ In file included from drivers/net/can/usb/etas_es58x/es58x_core.h:22, from drivers/net/can/usb/etas_es58x/es58x_fd.c:17: drivers/net/can/usb/etas_es58x/es58x_fd.h:231:6: note: while referencing 'raw_msg' 231 | u8 raw_msg[0]; | ^~~~~~~ Cc: Wolfgang Grandegger <wg@grandegger.com> Cc: Marc Kleine-Budde <mkl@pengutronix.de> Cc: "David S. Miller" <davem@davemloft.net> Cc: Jakub Kicinski <kuba@kernel.org> Cc: Arunachalam Santhanam <arunachalam.santhanam@in.bosch.com> Cc: Vincent Mailhol <mailhol.vincent@wanadoo.fr> Cc: linux-can@vger.kernel.org Cc: netdev@vger.kernel.org Signed-off-by: Kees Cook <keescook@chromium.org> --- drivers/net/can/usb/etas_es58x/es581_4.h | 2 +- drivers/net/can/usb/etas_es58x/es58x_fd.h | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-)