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: sta...@vger.kernel.org
Signed-off-by: Grant Hernandez <granthernan...@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 sh...@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] = '-';
--
2.22.0.410.gd8fdbe21b5-goog
