From c9fcba15565f3db7232489366c87c298c4198b0a Mon Sep 17 00:00:00 2001

From: Grant Hernandez <granthernandez@google.com>

Date: Thu, 11 Jul 2019 15:22:32 -0700

Subject: [PATCH] Input: gtco - bounds check collection indent level

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.

Cc: stable@vger.kernel.org

Signed-off-by: Grant Hernandez <granthernandez@google.com>

---

 drivers/input/tablet/gtco.c | 19 ++++++++++++++++---

 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/drivers/input/tablet/gtco.c b/drivers/input/tablet/gtco.c

index 4b8b9d7aa75e..9771052ed027 100644

--- 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 */

@@ -223,8 +224,7 @@ static void parse_hid_report_descriptor(struct gtco *device, char * report,

 	char  maintype = 'x';

 	char  globtype[12];

 	int   indent = 0;

-	char  indentstr[10] = "";

-

+	char  indentstr[MAX_COLLECTION_LEVELS+1] = {0};

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

@@ -350,6 +350,12 @@ static void parse_hid_report_descriptor(struct gtco *device, char * report,

 			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");

@@ -369,8 +375,15 @@ static void parse_hid_report_descriptor(struct gtco *device, char * report,

 				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] = '-';

-- 

2.21.0