| Message ID | 20210920123045.795228-1-arnd@kernel.org |
|---|---|
| State | New |
| Headers | show |
| Series | can: etas_es58x: avoid -Wzero-length-bounds warning | expand |
Hi Arnd, +CC: Kees Cook On Mon. 20 Sep 2021 at 21:30, Arnd Bergmann <arnd@kernel.org> wrote: > From: Arnd Bergmann <arnd@arndb.de> > > gcc complains when writing into a zero-length array: > > drivers/net/can/usb/etas_es58x/es581_4.c: In function 'es581_4_tx_can_msg': > drivers/net/can/usb/etas_es58x/es581_4.c:374:42: warning: array subscript 65535 is outside the bounds of an interior zero-length array 'u8[0]' {aka 'unsigned char[]'} [-Wzero-length-bounds] > 374 | tx_can_msg = (typeof(tx_can_msg))&es581_4_urb_cmd->raw_msg[msg_len]; > | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > In file included from drivers/net/can/usb/etas_es58x/es58x_core.h:21, > from drivers/net/can/usb/etas_es58x/es581_4.c:15: > drivers/net/can/usb/etas_es58x/es581_4.h:195:20: note: while referencing 'raw_msg' > 195 | u8 raw_msg[0]; > | ^~~~~~~ > CC [M] drivers/net/can/usb/etas_es58x/es58x_fd.o > 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:360:42: 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:222:20: note: while referencing 'raw_msg' > 222 | u8 raw_msg[0]; > | ^~~~~~~ > > The solution is usually to use a flexible-array member the struct, but > we can't directly have that inside of a union, nor can it be the only > member of a struct, so add a dummy struct with another zero-length > member to get the intended behavior. > > If someone has a better workaround, let me know and I can send a new > patch, as this version is rather ugly. Actually, there is one. Kees Cook introduced a new macro, DECLARE_FLEX_ARRAY(), to do this in a more elegant way: https://lkml.org/lkml/2021/8/27/524 The same series also fixes the warning in the etas_es58x driver: https://lkml.org/lkml/2021/8/27/523 So we only need to wait for Kees's series to get merged :) Yours sincerely, Vincent Mailhol
diff --git a/drivers/net/can/usb/etas_es58x/es581_4.h b/drivers/net/can/usb/etas_es58x/es581_4.h index 4bc60a6df697..ac5ef88db565 100644 --- a/drivers/net/can/usb/etas_es58x/es581_4.h +++ b/drivers/net/can/usb/etas_es58x/es581_4.h @@ -192,7 +192,10 @@ 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]; + struct { + u8 __pad[0]; + 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 a191891b8777..253e7bafd0b6 100644 --- a/drivers/net/can/usb/etas_es58x/es58x_fd.h +++ b/drivers/net/can/usb/etas_es58x/es58x_fd.h @@ -219,7 +219,10 @@ 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]; + struct { + u8 __pad[0]; + u8 raw_msg[]; + }; } __packed; __le16 reserved_for_crc16_do_not_use;