CVE-2020-11609: NULL Pointer Dereference (CWE-476)
value: An issue was discovered in the stv06xx subsystem in the Linux kernel before 5.6.1. drivers/media/usb/gspca/stv06xx/stv06xx.c and drivers/media/usb/gspca/stv06xx/stv06xx_pb0100.c mishandle invalid descriptors, as demonstrated by a NULL pointer dereference, aka CID-485b06aadb93.
CWE description: The product dereferences a pointer that it expects to be valid but is NULL.
CVSS v3 base score: 4.3
Published: 2020-04-07T17:15Z
Repository: https://github.com/torvalds/linux
Language: C
Files changed: drivers/media/usb/gspca/stv06xx/stv06xx.c, drivers/media/usb/gspca/stv06xx/stv06xx_pb0100.c
Commit date: 2020-03-12 17:26:42 +0100
Commit message: media: stv06xx: add missing descriptor sanity checks

Make sure to check that we have two alternate settings and at least one
endpoint before accessing the second altsetting structure and
dereferencing the endpoint arrays.

This specifically avoids dereferencing NULL-pointers or corrupting
memory when a device does not have the expected descriptors.

Note that the sanity checks in stv06xx_start() and pb0100_start() are
not redundant as the driver is mixing looking up altsettings by index
and by number, which may not coincide.

Fixes: 8668d504d72c ("V4L/DVB (12082): gspca_stv06xx: Add support for st6422 bridge and sensor")
Fixes: c0b33bdc5b8d ("[media] gspca-stv06xx: support bandwidth changing")
Cc: stable <stable@vger.kernel.org>     # 2.6.31
Cc: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

Diff: diff --git a/drivers/media/usb/gspca/stv06xx/stv06xx.c b/drivers/media/usb/gspca/stv06xx/stv06xx.c
index 79653d409951..95673fc0a99c 100644
--- a/drivers/media/usb/gspca/stv06xx/stv06xx.c
+++ b/drivers/media/usb/gspca/stv06xx/stv06xx.c
@@ -280,10 +280,13 @@ static int stv06xx_start(struct gspca_dev *gspca_dev)
 	if (!alt) {
 		gspca_err(gspca_dev, "Couldn't get altsetting\n");
 		return -EIO;
 	}
 
+	if (alt->desc.bNumEndpoints < 1)
+		return -ENODEV;
+
 	packet_size = le16_to_cpu(alt->endpoint[0].desc.wMaxPacketSize);
 	err = stv06xx_write_bridge(sd, STV_ISO_SIZE_L, packet_size);
 	if (err < 0)
 		return err;
 
@@ -304,15 +307,25 @@ static int stv06xx_start(struct gspca_dev *gspca_dev)
 	return (err < 0) ? err : 0;
 }
 
 static int stv06xx_isoc_init(struct gspca_dev *gspca_dev)
 {
+	struct usb_interface_cache *intfc;
 	struct usb_host_interface *alt;
 	struct sd *sd = (struct sd *) gspca_dev;
 
+	intfc = gspca_dev->dev->actconfig->intf_cache[0];
+
+	if (intfc->num_altsetting < 2)
+		return -ENODEV;
+
+	alt = &intfc->altsetting[1];
+
+	if (alt->desc.bNumEndpoints < 1)
+		return -ENODEV;
+
 	/* Start isoc bandwidth "negotiation" at max isoc bandwidth */
-	alt = &gspca_dev->dev->actconfig->intf_cache[0]->altsetting[1];
 	alt->endpoint[0].desc.wMaxPacketSize =
 		cpu_to_le16(sd->sensor->max_packet_size[gspca_dev->curr_mode]);
 
 	return 0;
 }
@@ -321,10 +334,14 @@ static int stv06xx_isoc_nego(struct gspca_dev *gspca_dev)
 {
 	int ret, packet_size, min_packet_size;
 	struct usb_host_interface *alt;
 	struct sd *sd = (struct sd *) gspca_dev;
 
+	/*
+	 * Existence of altsetting and endpoint was verified in
+	 * stv06xx_isoc_init()
+	 */
 	alt = &gspca_dev->dev->actconfig->intf_cache[0]->altsetting[1];
 	packet_size = le16_to_cpu(alt->endpoint[0].desc.wMaxPacketSize);
 	min_packet_size = sd->sensor->min_packet_size[gspca_dev->curr_mode];
 	if (packet_size <= min_packet_size)
 		return -EIO;
diff --git a/drivers/media/usb/gspca/stv06xx/stv06xx_pb0100.c b/drivers/media/usb/gspca/stv06xx/stv06xx_pb0100.c
index 6d1007715ff7..ae382b3b5f7f 100644
--- a/drivers/media/usb/gspca/stv06xx/stv06xx_pb0100.c
+++ b/drivers/media/usb/gspca/stv06xx/stv06xx_pb0100.c
@@ -183,10 +183,14 @@ static int pb0100_start(struct sd *sd)
 
 	intf = usb_ifnum_to_if(sd->gspca_dev.dev, sd->gspca_dev.iface);
 	alt = usb_altnum_to_altsetting(intf, sd->gspca_dev.alt);
 	if (!alt)
 		return -ENODEV;
+
+	if (alt->desc.bNumEndpoints < 1)
+		return -ENODEV;
+
 	packet_size = le16_to_cpu(alt->endpoint[0].desc.wMaxPacketSize);
 
 	/* If we don't have enough bandwidth use a lower framerate */
 	max_packet_size = sd->sensor->max_packet_size[sd->gspca_dev.curr_mode];
 	if (packet_size < max_packet_size)

Vulnerable code: 	alt = &gspca_dev->dev->actconfig->intf_cache[0]->altsetting[1];
Fixed code: 	if (alt->desc.bNumEndpoints < 1)
		return -ENODEV;

	struct usb_interface_cache *intfc;
	intfc = gspca_dev->dev->actconfig->intf_cache[0];

	if (intfc->num_altsetting < 2)
		return -ENODEV;

	alt = &intfc->altsetting[1];

	if (alt->desc.bNumEndpoints < 1)
		return -ENODEV;

	/*
	 * Existence of altsetting and endpoint was verified in
	 * stv06xx_isoc_init()
	 */

	if (alt->desc.bNumEndpoints < 1)
		return -ENODEV;