net: add a recursion limit in xmit path

As tunnel devices are going to be lockless, we need to make sure a
misconfigured machine wont enter an infinite loop.

Add a percpu variable, and limit to three the number of stacked xmits.

Reported-by: Jesse Gross <jesse@nicira.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/dev.c b/net/core/dev.c
index 48ad47f..50dacca 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2177,6 +2177,9 @@ static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q,
        return rc;
 }
 
+static DEFINE_PER_CPU(int, xmit_recursion);
+#define RECURSION_LIMIT 3
+
 /**
  *     dev_queue_xmit - transmit a buffer
  *     @skb: buffer to transmit
@@ -2242,10 +2245,15 @@ int dev_queue_xmit(struct sk_buff *skb)
 
                if (txq->xmit_lock_owner != cpu) {
 
+                       if (__this_cpu_read(xmit_recursion) > RECURSION_LIMIT)
+                               goto recursion_alert;
+
                        HARD_TX_LOCK(dev, txq, cpu);
 
                        if (!netif_tx_queue_stopped(txq)) {
+                               __this_cpu_inc(xmit_recursion);
                                rc = dev_hard_start_xmit(skb, dev, txq);
+                               __this_cpu_dec(xmit_recursion);
                                if (dev_xmit_complete(rc)) {
                                        HARD_TX_UNLOCK(dev, txq);
                                        goto out;
@@ -2257,7 +2265,9 @@ int dev_queue_xmit(struct sk_buff *skb)
                                       "queue packet!\n", dev->name);
                } else {
                        /* Recursion is detected! It is possible,
-                        * unfortunately */
+                        * unfortunately
+                        */
+recursion_alert:
                        if (net_ratelimit())
                                printk(KERN_CRIT "Dead loop on virtual device "
                                       "%s, fix it urgently!\n", dev->name);