[PATCH 4.4 058/158] Input: gtco - bounds check collection indent level

Greg Kroah-Hartman
2019-08-02T09:32:53Z

From: Grant Hernandez <granthernandez@google.com>

commit 2a017fd82c5402b3c8df5e3d6e5165d9e6147dc1 upstream.

The GTCO tablet input driver configures itself from an HID report sent
via USB during the initial enumeration process. Some debugging messages
are generated during the parsing. A debugging message indentation
counter is not bounds checked, leading to the ability for a specially
crafted HID report to cause '-' and null bytes be written past the end
of the indentation array. As long as the kernel has CONFIG_DYNAMIC_DEBUG
enabled, this code will not be optimized out. This was discovered
during code review after a previous syzkaller bug was found in this
driver.

Signed-off-by: Grant Hernandez <granthernandez@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/input/tablet/gtco.c | 20 +++++++++++++++++---
1 file changed, 17 insertions(+), 3 deletions(-)

--- a/drivers/input/tablet/gtco.c
+++ b/drivers/input/tablet/gtco.c
@@ -78,6 +78,7 @@ Scott Hill shill@gtcocalcomp.com

/* Max size of a single report */
#define REPORT_MAX_SIZE 10
+#define MAX_COLLECTION_LEVELS 10

/* Bitmask whether pen is in range */
@@ -224,8 +225,7 @@ static void parse_hid_report_descriptor(
char maintype = 'x';
char globtype[12];
int indent = 0;
- char indentstr[10] = "";
-
+ char indentstr[MAX_COLLECTION_LEVELS + 1] = { 0 };

dev_dbg(ddev, "======>>>>>>PARSE<<<<<<======\n");

@@ -351,6 +351,13 @@ static void parse_hid_report_descriptor(
case TAG_MAIN_COL_START:
maintype = 'S';

+ if (indent == MAX_COLLECTION_LEVELS) {
+ dev_err(ddev, "Collection level %d would exceed limit of %d\n",
+ indent + 1,
+ MAX_COLLECTION_LEVELS);
+ break;
+ }
+
if (data == 0) {
dev_dbg(ddev, "======>>>>>> Physical\n");
strcpy(globtype, "Physical");
@@ -370,8 +377,15 @@ static void parse_hid_report_descriptor(
break;

case TAG_MAIN_COL_END:
- dev_dbg(ddev, "<<<<<<======\n");
maintype = 'E';
+
+ if (indent == 0) {
+ dev_err(ddev, "Collection level already at zero\n");
+ break;
+ }
+
+ dev_dbg(ddev, "<<<<<<======\n");
+
indent--;
for (x = 0; x < indent; x++)
indentstr[x] = '-';