[RFC v3 1/2] HID: core: Mitigate potential OOB by removing bogus memset()

[Lee Jones <lee@kernel.org>]

The memset() in hid_report_raw_event() has the good intention of
clearing out bogus data by zeroing the area from the end of the incoming
data string to the assumed end of the buffer.  However, as we have
previously seen, doing so can easily result in OOB reads and writes in
the subsequent thread of execution.

The current suggestion from one of the HID maintainers is to remove the
memset() and simply return if the incoming event buffer size is not
large enough to fill the associated report.

Suggested-by Benjamin Tissoires <bentiss@kernel.org>
Signed-off-by: Lee Jones <lee@kernel.org>
---
v2 -> v3: Instead of removing the check entirely, show a warning and return early

RFC query: Is it better to return SUCCESS or -EINVAL?

 drivers/hid/hid-core.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
index a5b3a8ca2fcb..da9231ca42bc 100644
--- a/drivers/hid/hid-core.c
+++ b/drivers/hid/hid-core.c
@@ -2057,9 +2057,9 @@ int hid_report_raw_event(struct hid_device *hid, enum hid_report_type type, u8 *
 		rsize = max_buffer_size;
 
 	if (csize < rsize) {
-		dbg_hid("report %d is too short, (%d < %d)\n", report->id,
-				csize, rsize);
-		memset(cdata + csize, 0, rsize - csize);
+		hid_warn_ratelimited(hid, "Event data for report %d was too short (%d vs %d)\n",
+				     report->id, rsize, csize);
+		goto out;
 	}
 
 	if ((hid->claimed & HID_CLAIMED_HIDDEV) && hid->hiddev_report_event)
-- 
2.53.0.473.g4a7958ca14-goog