[PATCH v3 1/2] media: s2255: check firmware size before reading trailing marker

[Lei Huang <huanglei814@163.com>]

From: Lei Huang <huanglei@kylinos.cn>

s2255_probe() reads a 4-byte marker and version from the last 8 bytes
of the firmware blob (fw->data[fw_size - 8] and [fw_size - 4]). If the
firmware file is shorter than 8 bytes, fw_size - 8 underflows and the
access reads out of bounds. Validate the firmware size before indexing.

Fixes: 14d962602c8b ("V4L/DVB (8752): s2255drv: firmware improvement patch")
Signed-off-by: Lei Huang <huanglei@kylinos.cn>
---
 drivers/media/usb/s2255/s2255drv.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/media/usb/s2255/s2255drv.c b/drivers/media/usb/s2255/s2255drv.c
index 0b8182edf8e4..3917913c3b47 100644
--- a/drivers/media/usb/s2255/s2255drv.c
+++ b/drivers/media/usb/s2255/s2255drv.c
@@ -2277,6 +2277,11 @@ static int s2255_probe(struct usb_interface *interface,
 	}
 	/* check the firmware is valid */
 	fw_size = dev->fw_data->fw->size;
+	if (fw_size < 8) {
+		dev_err(&interface->dev, "Firmware invalid: too small.\n");
+		retval = -ENODEV;
+		goto errorFWMARKER;
+	}
 	pdata = (__le32 *) &dev->fw_data->fw->data[fw_size - 8];
 
 	if (*pdata != S2255_FW_MARKER) {
-- 
2.25.1