Subject: Re: xen-netfront crash when detaching network while some network activity

From: David Vrabel <[email-masked]>
Date: Tue, 26 May 2015 11:56:00 +0100

On 22/05/15 12:49, Marek Marczykowski-Górecki wrote:
> Hi all,
> 
> I'm experiencing xen-netfront crash when doing xl network-detach while
> some network activity is going on at the same time. It happens only when
> domU has more than one vcpu. Not sure if this matters, but the backend
> is in another domU (not dom0). I'm using Xen 4.2.2. It happens on kernel
> 3.9.4 and 4.1-rc1 as well.
> 
> Steps to reproduce:
> 1. Start the domU with some network interface
> 2. Call there 'ping -f some-IP'
> 3. Call 'xl network-detach NAME 0'

There's a use-after-free in xennet_remove().  Does this patch fix it?

8<--------------------------------
xen-netfront: properly destroy queues when removing device

xennet_remove() freed the queues before freeing the netdevice which
results in a use-after-free when free_netdev() tries to delete the
napi instances that have already been freed.

Fix this by fully destroy the queues (which includes deleting the napi
instances) before freeing the netdevice.

Reported-by: Marek Marczykowski <[email-masked]>
Signed-off-by: David Vrabel <[email-masked]>
---
 drivers/net/xen-netfront.c |   15 ++-------------
 1 file changed, 2 insertions(+), 13 deletions(-)

diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
index 3f45afd..e031c94 100644
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -1698,6 +1698,7 @@ static void xennet_destroy_queues(struct netfront_info *info)
 
 		if (netif_running(info->netdev))
 			napi_disable(&queue->napi);
+		del_timer_sync(&queue->rx_refill_timer);
 		netif_napi_del(&queue->napi);
 	}
 
@@ -2102,9 +2103,6 @@ static const struct attribute_group xennet_dev_group = {
 static int xennet_remove(struct xenbus_device *dev)
 {
 	struct netfront_info *info = dev_get_drvdata(&dev->dev);
-	unsigned int num_queues = info->netdev->real_num_tx_queues;
-	struct netfront_queue *queue = NULL;
-	unsigned int i = 0;
 
 	dev_dbg(&dev->dev, "%s\n", dev->nodename);
 
@@ -2112,16 +2110,7 @@ static int xennet_remove(struct xenbus_device *dev)
 
 	unregister_netdev(info->netdev);
 
-	for (i = 0; i < num_queues; ++i) {
-		queue = &info->queues[i];
-		del_timer_sync(&queue->rx_refill_timer);
-	}
-
-	if (num_queues) {
-		kfree(info->queues);
-		info->queues = NULL;
-	}
-
+	xennet_destroy_queues(info);
 	xennet_free_netdev(info->netdev);
 
 	return 0;
-- 
1.7.10.4

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