HID: core: Correctly handle ReportSize being zero

commit bce1305c0ece3dc549663605e567655dd701752c upstream.

It appears that a ReportSize value of zero is legal, even if a bit
non-sensical. Most of the HID code seems to handle that gracefully,
except when computing the total size in bytes. When fed as input to
memset, this leads to some funky outcomes.

Detect the corner case and correctly compute the size.

Cc: [email protected]
Signed-off-by: Marc Zyngier <[email protected]>
Signed-off-by: Benjamin Tissoires <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Change-Id: I0a1ae2d069cc8be1c1411ca25fb5c7bfec2ec2a2

Author: Marc Zyngier

Diff for: drivers/hid/hid-core.c

@@ -1343,6 +1343,17 @@ static void hid_output_field(const struct hid_device *hid,
 	}
 }
 
+/*
+ * Compute the size of a report.
+ */
+static size_t hid_compute_report_size(struct hid_report *report)
+{
+	if (report->size)
+		return ((report->size - 1) >> 3) + 1;
+
+	return 0;
+}
+
 /*
  * Create a report. 'data' has to be allocated using
  * hid_alloc_report_buf() so that it has proper size.
@@ -1355,7 +1366,7 @@ void hid_output_report(struct hid_report *report, __u8 *data)
 	if (report->id > 0)
 		*data++ = report->id;
 
-	memset(data, 0, ((report->size - 1) >> 3) + 1);
+	memset(data, 0, hid_compute_report_size(report));
 	for (n = 0; n < report->maxfield; n++)
 		hid_output_field(report->device, report->field[n], data);
 }
@@ -1482,7 +1493,7 @@ int hid_report_raw_event(struct hid_device *hid, int type, u8 *data, u32 size,
 		csize--;
 	}
 
-	rsize = ((report->size - 1) >> 3) + 1;
+	rsize = hid_compute_report_size(report);
 
 	if (rsize > HID_MAX_BUFFER_SIZE)
 		rsize = HID_MAX_BUFFER_SIZE;