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[PATCH 4.4 17/25] USB: serial: digi_acceleport: fix OOB data sanity check

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

------------------

From: Johan Hovold <johan@kernel.org>

commit 2d380889215fe20b8523345649dee0579821800c upstream.

Make sure to check for short transfers to avoid underflow in a loop
condition when parsing the receive buffer.

Also fix an off-by-one error in the incomplete sanity check which could
lead to invalid data being parsed.

Fixes: 8c209e6782ca ("USB: make actual_length in struct urb field u32")
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/usb/serial/digi_acceleport.c |   14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

--- a/drivers/usb/serial/digi_acceleport.c
+++ b/drivers/usb/serial/digi_acceleport.c
@@ -1483,16 +1483,20 @@ static int digi_read_oob_callback(struct
 	struct usb_serial *serial = port->serial;
 	struct tty_struct *tty;
 	struct digi_port *priv = usb_get_serial_port_data(port);
+	unsigned char *buf = urb->transfer_buffer;
 	int opcode, line, status, val;
 	int i;
 	unsigned int rts;
 
+	if (urb->actual_length < 4)
+		return -1;
+
 	/* handle each oob command */
-	for (i = 0; i < urb->actual_length - 3;) {
-		opcode = ((unsigned char *)urb->transfer_buffer)[i++];
-		line = ((unsigned char *)urb->transfer_buffer)[i++];
-		status = ((unsigned char *)urb->transfer_buffer)[i++];
-		val = ((unsigned char *)urb->transfer_buffer)[i++];
+	for (i = 0; i < urb->actual_length - 4; i += 4) {
+		opcode = buf[i];
+		line = buf[i + 1];
+		status = buf[i + 2];
+		val = buf[i + 3];
 
 		dev_dbg(&port->dev, "digi_read_oob_callback: opcode=%d, line=%d, status=%d, val=%d\n",
 			opcode, line, status, val);

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[PATCH 4.4 17/25] USB: serial: digi_acceleport: fix OOB data sanity check Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-24 09:30 +0100
  Re: [PATCH 4.4 17/25] USB: serial: digi_acceleport: fix OOB data  sanity check Ben Hutchings <ben@decadent.org.uk> - 2017-02-24 14:40 +0100
    Re: [PATCH 4.4 17/25] USB: serial: digi_acceleport: fix OOB data  sanity check Johan Hovold <johan@kernel.org> - 2017-02-24 18:40 +0100
      Re: [PATCH 4.4 17/25] USB: serial: digi_acceleport: fix OOB data  sanity check Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-24 19:00 +0100
        Re: [PATCH 4.4 17/25] USB: serial: digi_acceleport: fix OOB data  sanity check Johan Hovold <johan@kernel.org> - 2017-02-24 19:20 +0100

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