[PATCH v2 1/4] can: kvaser_usb: Don't free packets when tight on URBs

Ahmed S. Darwish
2014-12-24T23:56:44Z

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

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.

Signed-off-by: Ahmed S. Darwish <ahmed.darwish@valeo.com>
---
drivers/net/can/usb/kvaser_usb.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)

(Marc, Greg, I believe this should also be added to -stable?)

diff --git a/drivers/net/can/usb/kvaser_usb.c b/drivers/net/can/usb/kvaser_usb.c
index 541fb7a..6479a2b 100644
--- a/drivers/net/can/usb/kvaser_usb.c
+++ b/drivers/net/can/usb/kvaser_usb.c
@@ -1294,12 +1294,14 @@ static netdev_tx_t kvaser_usb_start_xmit(struct sk_buff *skb,
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;
}

@@ -1334,6 +1336,9 @@ static netdev_tx_t kvaser_usb_start_xmit(struct sk_buff *skb,
}
}

+ /*
+ * This should never happen; it implies a flow control bug.
+ */
if (!context) {
netdev_warn(netdev, "cannot find free context\n");
ret = NETDEV_TX_BUSY;
@@ -1364,9 +1369,6 @@ static netdev_tx_t kvaser_usb_start_xmit(struct sk_buff *skb,
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);

@@ -1388,8 +1390,6 @@ releasebuf:
kfree(buf);
nobufmem:
usb_free_urb(urb);
-nourbmem:
- dev_kfree_skb(skb);
return ret;
}