Re: [PATCH v2 2/5] treewide: Replace open-coded flex arrays in unions

Vincent MAILHOL
2021-08-28T07:31:35Z

Le sam. 28 août 2021 à 01:17, Kees Cook <keescook@chromium.org> a écrit :
>
> On Thu, Aug 26, 2021 at 08:24:52AM +0200, Marc Kleine-Budde wrote:
> > [...]
> > BTW: Is there opportunity for conversion, too?
> >
> > | drivers/net/can/peak_canfd/peak_pciefd_main.c:146:32: warning: array of flexible structures
>
> Untested potential solution:
>
> diff --git a/drivers/net/can/peak_canfd/peak_pciefd_main.c b/drivers/net/can/peak_canfd/peak_pciefd_main.c
> index 1df3c4b54f03..efa2b5a52bd7 100644
> --- a/drivers/net/can/peak_canfd/peak_pciefd_main.c
> +++ b/drivers/net/can/peak_canfd/peak_pciefd_main.c
> @@ -143,7 +143,11 @@ struct pciefd_rx_dma {
> __le32 irq_status;
> __le32 sys_time_low;
> __le32 sys_time_high;
> - struct pucan_rx_msg msg[];
> + /*
> + * with "msg" being pciefd_irq_rx_cnt(priv->irq_status)-many
> + * variable-sized struct pucan_rx_msg following.
> + */
> + __le32 msg[];

Isn't u8 msg[] preferable here?

> } __packed __aligned(4);
>
> /* Tx Link record */
> @@ -327,7 +331,7 @@ static irqreturn_t pciefd_irq_handler(int irq, void *arg)
>
> /* handle rx messages (if any) */
> peak_canfd_handle_msgs_list(&priv->ucan,
> - rx_dma->msg,
> + (struct pucan_rx_msg *)rx_dma->msg,
> pciefd_irq_rx_cnt(priv->irq_status));
>
> /* handle tx link interrupt (if any) */
>
>
> It's not great, but it's also not strictly a flex array, in the sense
> that since struct pucan_rx_msg is a variable size, the compiler cannot
> reason about the size of struct pciefd_rx_dma based only on the
> irq_status encoding...

In the same spirit, it is a bit cleaner to change the prototype of
handle_msgs_list().

Like that:

diff --git a/drivers/net/can/peak_canfd/peak_canfd.c b/drivers/net/can/peak_canf
d/peak_canfd.c
index d08718e98e11..81a9faa6193f 100644
--- a/drivers/net/can/peak_canfd/peak_canfd.c
+++ b/drivers/net/can/peak_canfd/peak_canfd.c
@@ -484,9 +484,8 @@ int peak_canfd_handle_msg(struct peak_canfd_priv *priv,

/* handle a list of rx_count messages from rx_msg memory address */
int peak_canfd_handle_msgs_list(struct peak_canfd_priv *priv,
- struct pucan_rx_msg *msg_list, int msg_count)
+ void *msg_ptr, int msg_count)
{
- void *msg_ptr = msg_list;
int i, msg_size = 0;

for (i = 0; i < msg_count; i++) {
diff --git a/drivers/net/can/peak_canfd/peak_canfd_user.h b/drivers/net/can/peak
_canfd/peak_canfd_user.h
index a72719dc3b74..ef91f92e70c3 100644
--- a/drivers/net/can/peak_canfd/peak_canfd_user.h
+++ b/drivers/net/can/peak_canfd/peak_canfd_user.h
@@ -42,5 +42,5 @@ struct net_device *alloc_peak_canfd_dev(int
sizeof_priv, int index,
int peak_canfd_handle_msg(struct peak_canfd_priv *priv,
struct pucan_rx_msg *msg);
int peak_canfd_handle_msgs_list(struct peak_canfd_priv *priv,
- struct pucan_rx_msg *rx_msg, int rx_count);
+ void *msg_ptr, int rx_count);
#endif
diff --git a/drivers/net/can/peak_canfd/peak_pciefd_main.c
b/drivers/net/can/peak_canfd/peak_pciefd_main.c
index 1df3c4b54f03..c1de1e3dc4bc 100644
--- a/drivers/net/can/peak_canfd/peak_pciefd_main.c
+++ b/drivers/net/can/peak_canfd/peak_pciefd_main.c
@@ -143,7 +143,11 @@ struct pciefd_rx_dma {
__le32 irq_status;
__le32 sys_time_low;
__le32 sys_time_high;
- struct pucan_rx_msg msg[];
+ /*
+ * with "msg" being pciefd_irq_rx_cnt(priv->irq_status)-many
+ * variable-sized struct pucan_rx_msg following.
+ */
+ u8 msg[];
} __packed __aligned(4);

/* Tx Link record */

Another solution would be to declare a maximum length for struct
pucan_rx_msg::d. Because these are CAN FD messages, I suppose
that maximum length would be CANFD_MAX_DLEN. struct canfd_frame
from the UAPI uses the same pattern.

N.B. This solution is not exclusive from the above one (actually,
I think that using both would be the best solution).

diff --git a/include/linux/can/dev/peak_canfd.h
b/include/linux/can/dev/peak_canfd.h
index f38772fd0c07..a048359db430 100644
--- a/include/linux/can/dev/peak_canfd.h
+++ b/include/linux/can/dev/peak_canfd.h
@@ -189,7 +189,7 @@ struct __packed pucan_rx_msg {
u8 client;
__le16 flags;
__le32 can_id;
- u8 d[];
+ u8 d[CANFD_MAX_DLEN];
};

/* uCAN error types */

I only tested for compilation.

Yours sincerely,
Vincent