Input: gtco - fix potential out-of-bound access

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>
Reviewed-by: Andrey Konovalov <andreyknvl@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

1 files changed, 10 insertions, 7 deletions

diff --git a/drivers/input/tablet/gtco.c b/drivers/input/tablet/gtco.c
index b796e891e2ee..4b8b9d7aa75e 100644
--- a/drivers/input/tablet/gtco.c
+++ b/drivers/input/tablet/gtco.c
@@ -230,13 +230,17 @@ 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);
+                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 +248,7 @@ 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;
                 }