On Wed. 18 Aug 2021 at 12:40, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> 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@xxxxxxxxxxxxxx>
> Cc: Marc Kleine-Budde <mkl@xxxxxxxxxxxxxx>
> Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
> Cc: Jakub Kicinski <kuba@xxxxxxxxxx>
> Cc: Arunachalam Santhanam <arunachalam.santhanam@xxxxxxxxxxxx>
> Cc: Vincent Mailhol <mailhol.vincent@xxxxxxxxxx>
> Cc: linux-can@xxxxxxxxxxxxxxx
> Cc: netdev@xxxxxxxxxxxxxxx
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> ---
> 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(-)
>
> 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;
> --
> 2.30.2
raw_msg is part of a union so its maximum size is implicitly the
biggest size of the other member of that union:
| struct es58x_fd_urb_cmd {
| __le16 SOF;
| u8 cmd_type;
| u8 cmd_id;
| u8 channel_idx;
| __le16 msg_len;
|
| union {
| 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;
| u8 raw_msg[0];
| } __packed;
|
| __le16 reserved_for_crc16_do_not_use;
| } __packed;
ram_msg can then be used to manipulate the other fields at the byte level.
I am sorry but I fail to understand why this is an issue.
Also, the proposed fix drastically increases the size of the structure.
Yours sincerely,
Vincent
