media: ov519: add missing endpoint sanity checks

CVE-2020-11608

Make sure to check that we have at least one endpoint before accessing
the endpoint array to avoid dereferencing a NULL-pointer on stream
start.

Note that these sanity checks are not redundant as the driver is mixing
looking up altsettings by index and by number, which need not coincide.

Fixes: 1876bb92 ("V4L/DVB (12079): gspca_ov519: add support for the ov511 bridge")
Fixes: b282d873 ("V4L/DVB (12080): gspca_ov519: Fix ov518+ with OV7620AE (Trust spacecam 320)")
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>
(cherry picked from commit 99891234)
Signed-off-by: Po-Hsu Lin <po-hsu.lin@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Acked-by: Khalid Elmously <khalid.elmously@canonical.com>
Signed-off-by: Kelsey Skunberg <kelsey.skunberg@canonical.com>

drivers/media/usb/gspca/ov519.c

@@ -3512,6 +3512,11 @@ static void ov511_mode_init_regs(struct sd *sd)
 		return;
 	}
 
+	if (alt->desc.bNumEndpoints < 1) {
+		sd->gspca_dev.usb_err = -ENODEV;
+		return;
+	}
+
 	packet_size = le16_to_cpu(alt->endpoint[0].desc.wMaxPacketSize);
 	reg_w(sd, R51x_FIFO_PSIZE, packet_size >> 5);
 
@@ -3642,6 +3647,11 @@ static void ov518_mode_init_regs(struct sd *sd)
 		return;
 	}
 
+	if (alt->desc.bNumEndpoints < 1) {
+		sd->gspca_dev.usb_err = -ENODEV;
+		return;
+	}
+
 	packet_size = le16_to_cpu(alt->endpoint[0].desc.wMaxPacketSize);
 	ov518_reg_w32(sd, R51x_FIFO_PSIZE, packet_size & ~7, 2);