[PATCH 3.12 017/142] USB: serial: safe_serial: fix information leak in completion handler

[Jiri Slaby]

From: Johan Hovold <johan@xxxxxxxxxx>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit 8c76d7cd520ebffc1ea9ea0850d87a224a50c7f2 upstream.

Add missing sanity check to the bulk-in completion handler to avoid an
integer underflow that could be triggered by a malicious device.

This avoids leaking up to 56 bytes from after the URB transfer buffer to
user space.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Johan Hovold <johan@xxxxxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
---
 drivers/usb/serial/safe_serial.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/usb/serial/safe_serial.c b/drivers/usb/serial/safe_serial.c
index ba895989d8c4..246cdefa0e88 100644
--- a/drivers/usb/serial/safe_serial.c
+++ b/drivers/usb/serial/safe_serial.c
@@ -206,6 +206,11 @@ static void safe_process_read_urb(struct urb *urb)
 	if (!safe)
 		goto out;
 
+	if (length < 2) {
+		dev_err(&port->dev, "malformed packet\n");
+		return;
+	}
+
 	fcs = fcs_compute10(data, length, CRC10_INITFCS);
 	if (fcs) {
 		dev_err(&port->dev, "%s - bad CRC %x\n", __func__, fcs);
-- 
2.12.2