[PATCH] Input: gtco - fix potential out-of-bound access

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

parse_hid_report_descriptor() has a while (i < length) loop, which
only guarantees that there's at least 1 byte in the buffer, but the
loop body can read multiple bytes which causes out-of-bounds access.

Reported-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
---
 drivers/input/tablet/gtco.c | 24 +++++++++++++++++-------
 1 file changed, 17 insertions(+), 7 deletions(-)

diff --git a/drivers/input/tablet/gtco.c b/drivers/input/tablet/gtco.c
index b796e891e2ee..0351203b8c24 100644
--- a/drivers/input/tablet/gtco.c
+++ b/drivers/input/tablet/gtco.c
@@ -230,13 +230,24 @@ static void parse_hid_report_descriptor(struct gtco *device, char * report,
 
 	/* Walk  this report and pull out the info we need */
 	while (i < length) {
-		prefix = report[i];
-
-		/* Skip over prefix */
-		i++;
+		prefix = report[i++];
 
 		/* Determine data size and save the data in the proper variable */
-		size = PREF_SIZE(prefix);
+		if (PREF_SIZE(prefix) < 1) {
+			dev_err(ddev,
+				"Invalid size %d in element at offset %d\n",
+				PREF_SIZE(prefix), i);
+			break;
+		}
+
+		size = 1U << (PREF_SIZE(prefix) - 1);
+		if (i + size >= length) {
+			dev_err(ddev,
+				"Not enough data (need %d, have %d)\n",
+				i + size, length);
+			break;
+		}
+
 		switch (size) {
 		case 1:
 			data = report[i];
@@ -244,8 +255,7 @@ static void parse_hid_report_descriptor(struct gtco *device, char * report,
 		case 2:
 			data16 = get_unaligned_le16(&report[i]);
 			break;
-		case 3:
-			size = 4;
+		case 4:
 			data32 = get_unaligned_le32(&report[i]);
 			break;
 		}
-- 
2.15.0.rc0.271.g36b669edcc-goog


-- 
Dmitry