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 <[email protected]>
Cc: Marc Kleine-Budde <[email protected]>
Cc: "David S. Miller" <[email protected]>
Cc: Jakub Kicinski <[email protected]>
Cc: Arunachalam Santhanam <[email protected]>
Cc: Vincent Mailhol <[email protected]>
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Kees Cook <[email protected]>
---
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
On Wed. 18 Aug 2021 at 12:40, Kees Cook <[email protected]> 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 <[email protected]>
> Cc: Marc Kleine-Budde <[email protected]>
> Cc: "David S. Miller" <[email protected]>
> Cc: Jakub Kicinski <[email protected]>
> Cc: Arunachalam Santhanam <[email protected]>
> Cc: Vincent Mailhol <[email protected]>
> Cc: [email protected]
> Cc: [email protected]
> Signed-off-by: Kees Cook <[email protected]>
> ---
> 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 <[email protected]> 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 <[email protected]>
> > Cc: Marc Kleine-Budde <[email protected]>
> > Cc: "David S. Miller" <[email protected]>
> > Cc: Jakub Kicinski <[email protected]>
> > Cc: Arunachalam Santhanam <[email protected]>
> > Cc: Vincent Mailhol <[email protected]>
> > Cc: [email protected]
> > Cc: [email protected]
> > Signed-off-by: Kees Cook <[email protected]>
> > ---
> > 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
--
Kees Cook
On Wed. 18 Aug 2021 at 15:48, Kees Cook <[email protected]> wrote:
> On Wed, Aug 18, 2021 at 02:13:51PM +0900, Vincent MAILHOL wrote:
> > On Wed. 18 Aug 2021 at 12:40, Kees Cook <[email protected]> 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 <[email protected]>
> > > Cc: Marc Kleine-Budde <[email protected]>
> > > Cc: "David S. Miller" <[email protected]>
> > > Cc: Jakub Kicinski <[email protected]>
> > > Cc: Arunachalam Santhanam <[email protected]>
> > > Cc: Vincent Mailhol <[email protected]>
> > > Cc: [email protected]
> > > Cc: [email protected]
> > > Signed-off-by: Kees Cook <[email protected]>
> > > ---
> > > 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/[email protected]/
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/[email protected]/#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
On Wed. 18 Aug 2021 at 18:03, Kees Cook <[email protected]> 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/[email protected]/
>
> 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/[email protected]/#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 <[email protected]> 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/[email protected]/
> >
> > 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/[email protected]/#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!
--
Kees Cook