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

[Dmitry Torokhov]

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 <andreyk...@google.com>
Signed-off-by: Dmitry Torokhov <dmitry.torok...@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