linux-kernel - [PATCH][next] mei: Avoid the use of one-element arrays

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Date:   Tue, 14 Jul 2020 12:46:44 -0500
From:   "Gustavo A. R. Silva" <gustavoars@...nel.org>
To:     Tomas Winkler <tomas.winkler@...el.com>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>
Subject: [PATCH][next] mei: Avoid the use of one-element arrays

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 or, as in this particular case, replace the one-element array
with a simple value type u8 reserved once this is just a placeholder
for alignment. The older style of one-element or zero-length arrays
should no longer be used[2].

Also, while there, use the preferred form for passing a size of a struct.
The alternative form where struct name is spelled out hurts readability
and introduces an opportunity for a bug when the variable type is changed
but the corresponding sizeof that is passed as argument is not.

[1] https://en.wikipedia.org/wiki/Flexible_array_member
[2] https://github.com/KSPP/linux/issues/79

Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
---
 drivers/misc/mei/hbm.c | 4 ++--
 drivers/misc/mei/hw.h  | 6 +++---
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/misc/mei/hbm.c b/drivers/misc/mei/hbm.c
index a44094cdbc36..f020d5594154 100644
--- a/drivers/misc/mei/hbm.c
+++ b/drivers/misc/mei/hbm.c
@@ -408,14 +408,14 @@ static int mei_hbm_add_cl_resp(struct mei_device *dev, u8 addr, u8 status)
 {
 	struct mei_msg_hdr mei_hdr;
 	struct hbm_add_client_response resp;
-	const size_t len = sizeof(struct hbm_add_client_response);
+	const size_t len = sizeof(resp);
 	int ret;
 
 	dev_dbg(dev->dev, "adding client response\n");
 
 	mei_hbm_hdr(&mei_hdr, len);
 
-	memset(&resp, 0, sizeof(struct hbm_add_client_response));
+	memset(&resp, 0, len);
 	resp.hbm_cmd = MEI_HBM_ADD_CLIENT_RES_CMD;
 	resp.me_addr = addr;
 	resp.status  = status;
diff --git a/drivers/misc/mei/hw.h b/drivers/misc/mei/hw.h
index b1a8d5ec88b3..8c0297f0e7f3 100644
--- a/drivers/misc/mei/hw.h
+++ b/drivers/misc/mei/hw.h
@@ -346,13 +346,13 @@ struct hbm_add_client_request {
  * @hbm_cmd: bus message command header
  * @me_addr: address of the client in ME
  * @status: if HBMS_SUCCESS then the client can now accept connections.
- * @reserved: reserved
+ * @reserved: reserved for alignment.
  */
 struct hbm_add_client_response {
 	u8 hbm_cmd;
 	u8 me_addr;
 	u8 status;
-	u8 reserved[1];
+	u8 reserved;
 } __packed;
 
 /**
@@ -461,7 +461,7 @@ struct hbm_notification {
 	u8 hbm_cmd;
 	u8 me_addr;
 	u8 host_addr;
-	u8 reserved[1];
+	u8 reserved;
 } __packed;
 
 /**
-- 
2.27.0