Commit ec764bf0 authored by Koki Sanagi's avatar Koki Sanagi Committed by David S. Miller
Browse files

net: tracepoint of net_dev_xmit sees freed skb and causes panic 



Because there is a possibility that skb is kfree_skb()ed and zero cleared
after ndo_start_xmit, we should not see the contents of skb like skb->len and
skb->dev->name after ndo_start_xmit. But trace_net_dev_xmit does that
and causes panic by NULL pointer dereference.
This patch fixes trace_net_dev_xmit not to see the contents of skb directly.

If you want to reproduce this panic,

1. Get tracepoint of net_dev_xmit on
2. Create 2 guests on KVM
2. Make 2 guests use virtio_net
4. Execute netperf from one to another for a long time as a network burden
5. host will panic(It takes about 30 minutes)

Signed-off-by: default avatarKoki Sanagi <sanagi.koki@jp.fujitsu.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 2e4ceec4

include/trace/events/net.h

+7 −5
Original line number Diff line number Diff line
@@ -12,22 +12,24 @@ 
TRACE_EVENT(net_dev_xmit,



	TP_PROTO(struct sk_buff *skb,

		 int rc),

		 int rc,

		 struct net_device *dev,

		 unsigned int skb_len),



	TP_ARGS(skb, rc),

	TP_ARGS(skb, rc, dev, skb_len),



	TP_STRUCT__entry(

		__field(	void *,		skbaddr		)

		__field(	unsigned int,	len		)

		__field(	int,		rc		)

		__string(	name,		skb->dev->name	)

		__string(	name,		dev->name	)

	),



	TP_fast_assign(

		__entry->skbaddr = skb;

		__entry->len = skb->len;

		__entry->len = skb_len;

		__entry->rc = rc;

		__assign_str(name, skb->dev->name);

		__assign_str(name, dev->name);

	),



	TP_printk("dev=%s skbaddr=%p len=%u rc=%d",

net/core/dev.c

+5 −2
Original line number Diff line number Diff line
@@ -2096,6 +2096,7 @@ int dev_hard_start_xmit(struct sk_buff *skb, struct net_device *dev, 
{

	const struct net_device_ops *ops = dev->netdev_ops;

	int rc = NETDEV_TX_OK;

	unsigned int skb_len;



	if (likely(!skb->next)) {

		u32 features;
@@ -2146,8 +2147,9 @@ int dev_hard_start_xmit(struct sk_buff *skb, struct net_device *dev, 
			}

		}



		skb_len = skb->len;

		rc = ops->ndo_start_xmit(skb, dev);

		trace_net_dev_xmit(skb, rc);

		trace_net_dev_xmit(skb, rc, dev, skb_len);

		if (rc == NETDEV_TX_OK)

			txq_trans_update(txq);

		return rc;
@@ -2167,8 +2169,9 @@ gso: 
		if (dev->priv_flags & IFF_XMIT_DST_RELEASE)

			skb_dst_drop(nskb);



		skb_len = nskb->len;

		rc = ops->ndo_start_xmit(nskb, dev);

		trace_net_dev_xmit(nskb, rc);

		trace_net_dev_xmit(nskb, rc, dev, skb_len);

		if (unlikely(rc != NETDEV_TX_OK)) {

			if (rc & ~NETDEV_TX_MASK)

				goto out_kfree_gso_skb;

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