[PATCH v2 1/4][next] scsi: megaraid_sas: Replace one-element array with flexible-array member in MR_FW_RAID_MAP

["Gustavo A. R. Silva" <gustavoars@kernel.org>]

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].

Refactor the code according to the use of a flexible-array member in struct
MR_FW_RAID_MAP instead of one-element array, and use the struct_size()
helper.

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().

[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>
---
Changes in v2:
 - Revert changes in struct MR_FW_RAID_MAP_ALL.
 - Update Subject line and changelog text.

 drivers/scsi/megaraid/megaraid_sas_base.c   | 6 +++---
 drivers/scsi/megaraid/megaraid_sas_fp.c     | 6 +++---
 drivers/scsi/megaraid/megaraid_sas_fusion.h | 2 +-
 3 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/drivers/scsi/megaraid/megaraid_sas_base.c b/drivers/scsi/megaraid/megaraid_sas_base.c
index ec10b2497310..d072f9caeb4a 100644
--- a/drivers/scsi/megaraid/megaraid_sas_base.c
+++ b/drivers/scsi/megaraid/megaraid_sas_base.c
@@ -5147,9 +5147,9 @@ static void megasas_update_ext_vd_details(struct megasas_instance *instance)
 		fusion->current_map_sz = ventura_map_sz;
 		fusion->max_map_sz = ventura_map_sz;
 	} else {
-		fusion->old_map_sz =  sizeof(struct MR_FW_RAID_MAP) +
-					(sizeof(struct MR_LD_SPAN_MAP) *
-					(instance->fw_supported_vd_count - 1));
+		fusion->old_map_sz =
+			struct_size((struct MR_FW_RAID_MAP *)0, ldSpanMap,
+				    instance->fw_supported_vd_count);
 		fusion->new_map_sz =  sizeof(struct MR_FW_RAID_MAP_EXT);
 
 		fusion->max_map_sz =
diff --git a/drivers/scsi/megaraid/megaraid_sas_fp.c b/drivers/scsi/megaraid/megaraid_sas_fp.c
index 83f69c33b01a..da1cad1ee123 100644
--- a/drivers/scsi/megaraid/megaraid_sas_fp.c
+++ b/drivers/scsi/megaraid/megaraid_sas_fp.c
@@ -326,9 +326,9 @@ u8 MR_ValidateMapInfo(struct megasas_instance *instance, u64 map_id)
 	else if (instance->supportmax256vd)
 		expected_size = sizeof(struct MR_FW_RAID_MAP_EXT);
 	else
-		expected_size =
-			(sizeof(struct MR_FW_RAID_MAP) - sizeof(struct MR_LD_SPAN_MAP) +
-			(sizeof(struct MR_LD_SPAN_MAP) * le16_to_cpu(pDrvRaidMap->ldCount)));
+		expected_size = struct_size((struct MR_FW_RAID_MAP *)0,
+					    ldSpanMap,
+					    le16_to_cpu(pDrvRaidMap->ldCount));
 
 	if (le32_to_cpu(pDrvRaidMap->totalSize) != expected_size) {
 		dev_dbg(&instance->pdev->dev, "megasas: map info structure size 0x%x",
diff --git a/drivers/scsi/megaraid/megaraid_sas_fusion.h b/drivers/scsi/megaraid/megaraid_sas_fusion.h
index ce84f811e5e1..a47139ef9ee2 100644
--- a/drivers/scsi/megaraid/megaraid_sas_fusion.h
+++ b/drivers/scsi/megaraid/megaraid_sas_fusion.h
@@ -942,7 +942,7 @@ struct MR_FW_RAID_MAP {
 	u8                  reserved2[7];
 	struct MR_ARRAY_INFO       arMapInfo[MAX_RAIDMAP_ARRAYS];
 	struct MR_DEV_HANDLE_INFO  devHndlInfo[MAX_RAIDMAP_PHYSICAL_DEVICES];
-	struct MR_LD_SPAN_MAP      ldSpanMap[1];
+	struct MR_LD_SPAN_MAP      ldSpanMap[];
 };
 
 struct IO_REQUEST_INFO {
-- 
2.27.0