HID: core: Correctly handle ReportSize being zero

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: stable@vger.kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@gmail.com>

diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
index 359616e3efbbb244e633b4a37ae6361c30abf19f..d2ecc9c4525548c5ae4f1f1a54de70d61c52a91d 100644 (file)
--- a/drivers/hid/hid-core.c
+++ b/drivers/hid/hid-core.c
@@ -1597,6 +1597,17 @@ 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.
@@ -1609,7 +1620,7 @@ 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);
 }
@@ -1739,7 +1750,7 @@ 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 (report_enum->numbered && rsize >= HID_MAX_BUFFER_SIZE)
                rsize = HID_MAX_BUFFER_SIZE - 1;