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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Johan Hovold <johan@kernel.org>
Subject: [PATCH 4.9 112/117] USB: serial: cyberjack: fix write-URB completion race
Date:   Mon,  9 Nov 2020 13:55:38 +0100
Message-Id: <20201109125031.012382267@linuxfoundation.org>
In-Reply-To: <20201109125025.630721781@linuxfoundation.org>
References: <20201109125025.630721781@linuxfoundation.org>
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From: Johan Hovold <johan@kernel.org>

commit 985616f0457d9f555fff417d0da56174f70cc14f upstream.

The write-URB busy flag was being cleared before the completion handler
was done with the URB, something which could lead to corrupt transfers
due to a racing write request if the URB is resubmitted.

Fixes: 507ca9bc0476 ("[PATCH] USB: add ability for usb-serial drivers to determine if their write urb is currently being used.")
Cc: stable <stable@vger.kernel.org>     # 2.6.13
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/cyberjack.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

--- a/drivers/usb/serial/cyberjack.c
+++ b/drivers/usb/serial/cyberjack.c
@@ -367,11 +367,12 @@ static void cyberjack_write_bulk_callbac
 	struct cyberjack_private *priv = usb_get_serial_port_data(port);
 	struct device *dev = &port->dev;
 	int status = urb->status;
+	bool resubmitted = false;
 
-	set_bit(0, &port->write_urbs_free);
 	if (status) {
 		dev_dbg(dev, "%s - nonzero write bulk status received: %d\n",
 			__func__, status);
+		set_bit(0, &port->write_urbs_free);
 		return;
 	}
 
@@ -404,6 +405,8 @@ static void cyberjack_write_bulk_callbac
 			goto exit;
 		}
 
+		resubmitted = true;
+
 		dev_dbg(dev, "%s - priv->wrsent=%d\n", __func__, priv->wrsent);
 		dev_dbg(dev, "%s - priv->wrfilled=%d\n", __func__, priv->wrfilled);
 
@@ -420,6 +423,8 @@ static void cyberjack_write_bulk_callbac
 
 exit:
 	spin_unlock(&priv->lock);
+	if (!resubmitted)
+		set_bit(0, &port->write_urbs_free);
 	usb_serial_port_softint(port);
 }