Currently struct wmi_host_mem_chunks defines:
	struct host_memory_chunk items[1];

Per the guidance in [1] this should be a flexible array. However there
is a documented requirement:
	some fw revisions require at least 1 chunk regardless of count

To satisfy this requirement, follow the guidance from [2] and wrap the
array in a union which contains both the flexible array and a single
instance of the underlying struct. Since the footprint of the struct
is unchanged, no additional driver changes are required.

No functional changes, compile tested only.

[1] https://docs.kernel.org/process/deprecated.html#zero-length-and-one-element-arrays
[2] https://lore.kernel.org/linux-wireless/202308301529.AC90A9EF98@keescook/

Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>
---
 drivers/net/wireless/ath/ath10k/wmi.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/net/wireless/ath/ath10k/wmi.h b/drivers/net/wireless/ath/ath10k/wmi.h
index 9146df98fcee..833ce0251a2c 100644
--- a/drivers/net/wireless/ath/ath10k/wmi.h
+++ b/drivers/net/wireless/ath/ath10k/wmi.h
@@ -3069,7 +3069,10 @@ struct host_memory_chunk {
 struct wmi_host_mem_chunks {
 	__le32 count;
 	/* some fw revisions require at least 1 chunk regardless of count */
-	struct host_memory_chunk items[1];
+	union {
+		struct host_memory_chunk item;
+		DECLARE_FLEX_ARRAY(struct host_memory_chunk, items);
+	};
 } __packed;
 
 struct wmi_init_cmd {

-- 
2.42.0

On 12/13/23 11:06, Jeff Johnson wrote:
> Currently struct wmi_host_mem_chunks defines:
> 	struct host_memory_chunk items[1];
> 
> Per the guidance in [1] this should be a flexible array. However there
> is a documented requirement:
> 	some fw revisions require at least 1 chunk regardless of count
> 
> To satisfy this requirement, follow the guidance from [2] and wrap the
> array in a union which contains both the flexible array and a single
> instance of the underlying struct. Since the footprint of the struct
> is unchanged, no additional driver changes are required.
> 
> No functional changes, compile tested only.
> 
> [1] https://docs.kernel.org/process/deprecated.html#zero-length-and-one-element-arrays
> [2] https://lore.kernel.org/linux-wireless/202308301529.AC90A9EF98@keescook/
> 
> Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>

Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>

Thanks!
--
Gustavo

> ---
>   drivers/net/wireless/ath/ath10k/wmi.h | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/wireless/ath/ath10k/wmi.h b/drivers/net/wireless/ath/ath10k/wmi.h
> index 9146df98fcee..833ce0251a2c 100644
> --- a/drivers/net/wireless/ath/ath10k/wmi.h
> +++ b/drivers/net/wireless/ath/ath10k/wmi.h
> @@ -3069,7 +3069,10 @@ struct host_memory_chunk {
>   struct wmi_host_mem_chunks {
>   	__le32 count;
>   	/* some fw revisions require at least 1 chunk regardless of count */
> -	struct host_memory_chunk items[1];
> +	union {
> +		struct host_memory_chunk item;
> +		DECLARE_FLEX_ARRAY(struct host_memory_chunk, items);
> +	};
>   } __packed;
>   
>   struct wmi_init_cmd {
>

On Wed, Dec 13, 2023 at 09:06:39AM -0800, Jeff Johnson wrote:
> Currently struct wmi_host_mem_chunks defines:
> 	struct host_memory_chunk items[1];
> 
> Per the guidance in [1] this should be a flexible array. However there
> is a documented requirement:
> 	some fw revisions require at least 1 chunk regardless of count
> 
> To satisfy this requirement, follow the guidance from [2] and wrap the
> array in a union which contains both the flexible array and a single
> instance of the underlying struct. Since the footprint of the struct
> is unchanged, no additional driver changes are required.
> 
> No functional changes, compile tested only.
> 
> [1] https://docs.kernel.org/process/deprecated.html#zero-length-and-one-element-arrays
> [2] https://lore.kernel.org/linux-wireless/202308301529.AC90A9EF98@keescook/
> 
> Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>

This looks like the right approach here.

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook