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

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Message-ID: <20171024163943.gpkmpgexfuqe5vun@dtor-ws>
Date:   Tue, 24 Oct 2017 09:39:43 -0700
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     linux-input@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Input: gtco - fix potential out-of-bound access

On Tue, Oct 24, 2017 at 01:04:03PM +0200, Andrey Konovalov wrote:
> On Tue, Oct 24, 2017 at 7:28 AM, Dmitry Torokhov
> <dmitry.torokhov@...il.com> wrote:
> > 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@...gle.com>
> > Signed-off-by: Dmitry Torokhov <dmitry.torokhov@...il.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) {
> 
> AFAIU PREF_SIZE(prefix) == 0 is a perfectly valid item data size.

Fair enough. How about the below instead then?

-- 
Dmitry


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

From: Dmitry Torokhov <dmitry.torokhov@...il.com>

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@...gle.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@...il.com>
---
 drivers/input/tablet/gtco.c |   17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/drivers/input/tablet/gtco.c b/drivers/input/tablet/gtco.c
index b796e891e2ee..7d8e9fb831c4 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 (size && 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;
 		}