[PATCH v2 22/63] HID: cp2112: Use struct_group() for memcpy() region

[Kees Cook]

In preparation for FORTIFY_SOURCE performing compile-time and run-time
field bounds checking for memcpy(), memmove(), and memset(), avoid
intentionally writing across neighboring fields.

Use struct_group() in struct cp2112_string_report around members report,
length, type, and string, so they can be referenced together. This will
allow memcpy() and sizeof() to more easily reason about sizes, improve
readability, and avoid future warnings about writing beyond the end of
report.

"pahole" shows no size nor member offset changes to struct
cp2112_string_report.  "objdump -d" shows no meaningful object
code changes (i.e. only source line number induced differences.)

Cc: Jiri Kosina <jikos at kernel.org>
Cc: Benjamin Tissoires <benjamin.tissoires at redhat.com>
Cc: linux-input at vger.kernel.org
Signed-off-by: Kees Cook <keescook at chromium.org>
---
 drivers/hid/hid-cp2112.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/drivers/hid/hid-cp2112.c b/drivers/hid/hid-cp2112.c
index 477baa30889c..ece147d1a278 100644
--- a/drivers/hid/hid-cp2112.c
+++ b/drivers/hid/hid-cp2112.c
@@ -129,10 +129,12 @@ struct cp2112_xfer_status_report {
 
 struct cp2112_string_report {
 	u8 dummy;		/* force .string to be aligned */
-	u8 report;		/* CP2112_*_STRING */
-	u8 length;		/* length in bytes of everyting after .report */
-	u8 type;		/* USB_DT_STRING */
-	wchar_t string[30];	/* UTF16_LITTLE_ENDIAN string */
+	struct_group_attr(contents, __packed,
+		u8 report;		/* CP2112_*_STRING */
+		u8 length;		/* length in bytes of everything after .report */
+		u8 type;		/* USB_DT_STRING */
+		wchar_t string[30];	/* UTF16_LITTLE_ENDIAN string */
+	);
 } __packed;
 
 /* Number of times to request transfer status before giving up waiting for a
@@ -986,8 +988,8 @@ static ssize_t pstr_show(struct device *kdev,
 	u8 length;
 	int ret;
 
-	ret = cp2112_hid_get(hdev, attr->report, &report.report,
-			     sizeof(report) - 1, HID_FEATURE_REPORT);
+	ret = cp2112_hid_get(hdev, attr->report, (u8 *)&report.contents,
+			     sizeof(report.contents), HID_FEATURE_REPORT);
 	if (ret < 3) {
 		hid_err(hdev, "error reading %s string: %d\n", kattr->attr.name,
 			ret);
-- 
2.30.2