[PATCH][next] mwifiex: usb: Replace one-element array with flexible-array member

There is a regular need in the kernel to provide a way to declare having
a dynamically sized set of trailing elements in a structure. Kernel code
should always use “flexible array members”[1] for these cases. The older
style of one-element or zero-length arrays should no longer be used[2].

This helps with the ongoing efforts to globally enable -Warray-bounds
and get us closer to being able to tighten the FORTIFY_SOURCE routines
on memcpy().

This issue was found with the help of Coccinelle and audited and fixed,
manually.

[1] https://en.wikipedia.org/wiki/Flexible_array_member
[2] https://www.kernel.org/doc/html/v5.10/process/deprecated.html#zero-length-and-one-element-arrays

Link: https://github.com/KSPP/linux/issues/79
Link: https://github.com/KSPP/linux/issues/109
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
 drivers/net/wireless/marvell/mwifiex/usb.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/wireless/marvell/mwifiex/usb.h b/drivers/net/wireless/marvell/mwifiex/usb.h
index d822ec15b7e6..61a96b7fbf21 100644
--- a/drivers/net/wireless/marvell/mwifiex/usb.h
+++ b/drivers/net/wireless/marvell/mwifiex/usb.h

@@ -134,7 +134,7 @@ struct fw_sync_header {
 struct fw_data {
 	struct fw_header fw_hdr;
 	__le32 seq_num;
-	u8 data[1];
+	u8 data[];
 } __packed;
 
 #endif /*_MWIFIEX_USB_H */

-- 
2.27.0

On Mon, Aug 9, 2021 at 2:08 PM Gustavo A. R. Silva
[off-list ref] wrote:

There is a regular need in the kernel to provide a way to declare having
a dynamically sized set of trailing elements in a structure. Kernel code
should always use “flexible array members”[1] for these cases. The older
style of one-element or zero-length arrays should no longer be used[2].

This helps with the ongoing efforts to globally enable -Warray-bounds
and get us closer to being able to tighten the FORTIFY_SOURCE routines
on memcpy().

This issue was found with the help of Coccinelle and audited and fixed,
manually.

[1] https://en.wikipedia.org/wiki/Flexible_array_member
[2] https://www.kernel.org/doc/html/v5.10/process/deprecated.html#zero-length-and-one-element-arrays

Link: https://github.com/KSPP/linux/issues/79
Link: https://github.com/KSPP/linux/issues/109
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>

An important part of your patch rationale should include determining
that the 1-length wasn't actually important anywhere. I double checked
for you, and nobody seemed to be relying on 'sizeof struct fw_data' at
all, so this should be OK:

Reviewed-by: Brian Norris <briannorris@chromium.org>

On 8/9/21 16:24, Brian Norris wrote:

On Mon, Aug 9, 2021 at 2:08 PM Gustavo A. R. Silva
[off-list ref] wrote:

quoted

There is a regular need in the kernel to provide a way to declare having
a dynamically sized set of trailing elements in a structure. Kernel code
should always use “flexible array members”[1] for these cases. The older
style of one-element or zero-length arrays should no longer be used[2].

This helps with the ongoing efforts to globally enable -Warray-bounds
and get us closer to being able to tighten the FORTIFY_SOURCE routines
on memcpy().

This issue was found with the help of Coccinelle and audited and fixed,
manually.

[1] https://en.wikipedia.org/wiki/Flexible_array_member
[2] https://www.kernel.org/doc/html/v5.10/process/deprecated.html#zero-length-and-one-element-arrays

Link: https://github.com/KSPP/linux/issues/79
Link: https://github.com/KSPP/linux/issues/109
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>

An important part of your patch rationale should include determining
that the 1-length wasn't actually important anywhere. I double checked
for you, and nobody seemed to be relying on 'sizeof struct fw_data' at
all, so this should be OK:

I always do that. That's the reason why I included this line in the
changelog text:

"This issue was found with the help of Coccinelle and audited and fixed,
manually."

Thanks for double-checking, though. :)

Reviewed-by: Brian Norris <briannorris@chromium.org>

Thanks
--
Gustavo

"Gustavo A. R. Silva" [off-list ref] wrote:

There is a regular need in the kernel to provide a way to declare having
a dynamically sized set of trailing elements in a structure. Kernel code
should always use “flexible array members”[1] for these cases. The older
style of one-element or zero-length arrays should no longer be used[2].

This helps with the ongoing efforts to globally enable -Warray-bounds
and get us closer to being able to tighten the FORTIFY_SOURCE routines
on memcpy().

This issue was found with the help of Coccinelle and audited and fixed,
manually.

[1] https://en.wikipedia.org/wiki/Flexible_array_member
[2] https://www.kernel.org/doc/html/v5.10/process/deprecated.html#zero-length-and-one-element-arrays

Link: https://github.com/KSPP/linux/issues/79
Link: https://github.com/KSPP/linux/issues/109
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Reviewed-by: Brian Norris <briannorris@chromium.org>

Patch applied to wireless-drivers-next.git, thanks.

090f2c5d3d07 mwifiex: usb: Replace one-element array with flexible-array member

-- 
https://patchwork.kernel.org/project/linux-wireless/patch/20210809211134.GA22488@embeddedor/

https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches