linux-kernel - [PATCH 3.14 68/98] can: kvaser_usb: Dont free packets when tight on URBs

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Message-Id: <20150125180715.789687130@linuxfoundation.org>
Date:	Sun, 25 Jan 2015 10:07:26 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Olivier Sobrie <olivier@...rie.be>,
	"Ahmed S. Darwish" <ahmed.darwish@...eo.com>,
	Marc Kleine-Budde <mkl@...gutronix.de>
Subject: [PATCH 3.14 68/98] can: kvaser_usb: Dont free packets when tight on URBs

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

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

From: "Ahmed S. Darwish" <ahmed.darwish@...eo.com>

commit b442723fcec445fb0ae1104888dd22cd285e0a91 upstream.

Flooding the Kvaser CAN to USB dongle with multiple reads and
writes in high frequency caused seemingly-random panics in the
kernel.

On further inspection, it seems the driver erroneously freed the
to-be-transmitted packet upon getting tight on URBs and returning
NETDEV_TX_BUSY, leading to invalid memory writes and double frees
at a later point in time.

Note:

Finding no more URBs/transmit-contexts and returning NETDEV_TX_BUSY
is a driver bug in and out of itself: it means that our start/stop
queue flow control is broken.

This patch only fixes the (buggy) error handling code; the root
cause shall be fixed in a later commit.

Acked-by: Olivier Sobrie <olivier@...rie.be>
Signed-off-by: Ahmed S. Darwish <ahmed.darwish@...eo.com>
Signed-off-by: Marc Kleine-Budde <mkl@...gutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/net/can/usb/kvaser_usb.c |   10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

--- a/drivers/net/can/usb/kvaser_usb.c
+++ b/drivers/net/can/usb/kvaser_usb.c
@@ -1285,12 +1285,14 @@ static netdev_tx_t kvaser_usb_start_xmit
 	if (!urb) {
 		netdev_err(netdev, "No memory left for URBs\n");
 		stats->tx_dropped++;
-		goto nourbmem;
+		dev_kfree_skb(skb);
+		return NETDEV_TX_OK;
 	}

 	buf = kmalloc(sizeof(struct kvaser_msg), GFP_ATOMIC);
 	if (!buf) {
 		stats->tx_dropped++;
+		dev_kfree_skb(skb);
 		goto nobufmem;
 	}

@@ -1325,6 +1327,7 @@ static netdev_tx_t kvaser_usb_start_xmit
 		}
 	}

+	/* This should never happen; it implies a flow control bug */
 	if (!context) {
 		netdev_warn(netdev, "cannot find free context\n");
 		ret =  NETDEV_TX_BUSY;
@@ -1355,9 +1358,6 @@ static netdev_tx_t kvaser_usb_start_xmit
 	if (unlikely(err)) {
 		can_free_echo_skb(netdev, context->echo_index);

-		skb = NULL; /* set to NULL to avoid double free in
-			     * dev_kfree_skb(skb) */
-
 		atomic_dec(&priv->active_tx_urbs);
 		usb_unanchor_urb(urb);

@@ -1379,8 +1379,6 @@ releasebuf:
 	kfree(buf);
 nobufmem:
 	usb_free_urb(urb);
-nourbmem:
-	dev_kfree_skb(skb);
 	return ret;
 }

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