| Message ID | 20210818034010.800652-1-keescook@chromium.org (mailing list archive) |
|---|---|
| State | Awaiting Upstream |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | can: etas_es58x: Replace 0-element raw_msg array | expand |
| Context | Check | Description |
|---|---|---|
| netdev/tree_selection | success | Series ignored based on subject |
On Wed. 18 Aug 2021 at 12:40, Kees Cook <keescook@chromium.org> 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@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(-) > > 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
On Wed, Aug 18, 2021 at 02:13:51PM +0900, Vincent MAILHOL wrote: > On Wed. 18 Aug 2021 at 12:40, Kees Cook <keescook@chromium.org> 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@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(-) > > > > 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: Yup, understood. See below... > > | 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. The issue is with using a 0-element array (these are being removed from the kernel[1] so we can add -Warray-bounds). Normally in this situation I would replace the 0-element array with a flexible array, but this case is unusual in several ways: - There is a trailing struct member (reserved_for_crc16_do_not_use), which is never accessed (good), and documented as "please never access this". - struct es58x_fd_urb_cmd is statically allocated (it is written into from the URB handler). - The message lengths coming from the USB device are stored in a u16, which looked like it was possible to overflow the buffer. In taking a closer look, I see that the URB command length is checked, and the in-data length is checked as well, so the overflow concern appears to be addressed. > Also, the proposed fix drastically increases the size of the structure. Indeed. I will send a v2, now that I see that the overflow concern isn't an issue. Thanks! -Kees [1] https://www.kernel.org/doc/html/latest/process/deprecated.html#zero-length-and-one-element-arrays
On Wed. 18 Aug 2021 at 15:48, Kees Cook <keescook@chromium.org> wrote: > On Wed, Aug 18, 2021 at 02:13:51PM +0900, Vincent MAILHOL wrote: > > On Wed. 18 Aug 2021 at 12:40, Kees Cook <keescook@chromium.org> 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@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(-) > > > > > > 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: > > Yup, understood. See below... > > > > > | 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. > > The issue is with using a 0-element array (these are being removed from > the kernel[1] so we can add -Warray-bounds). Normally in this situation I > would replace the 0-element array with a flexible array, but this > case is unusual in several ways: > > - There is a trailing struct member (reserved_for_crc16_do_not_use), > which is never accessed (good), and documented as "please never access > this". Yes. And FYI, this field is here so that | sizeof(struct es58x_fd_urb_cmd) returns the correct maximum size. And, of course, because this structure will be sent to the device, there is no possibility to reorder those fields. > - struct es58x_fd_urb_cmd is statically allocated (it is written into > from the URB handler). > > - The message lengths coming from the USB device are stored in a u16, > which looked like it was possible to overflow the buffer. > > In taking a closer look, I see that the URB command length is checked, > and the in-data length is checked as well, so the overflow concern > appears to be addressed. > > > Also, the proposed fix drastically increases the size of the structure. > > Indeed. I will send a v2, now that I see that the overflow concern isn't > an issue. Thanks for the explanation. That makes sense. 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? Yours sincerely, Vincent
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. :)
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 but the rest is clean. 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. I like the final result. I will do a bit more testing and give my acknowledgement if everything goes well. Yours sincerely, Vincent
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(-)