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Message-ID: <1285787072.2813.333.camel@edumazet-laptop> Date: Wed, 29 Sep 2010 21:04:32 +0200 From: Eric Dumazet <eric.dumazet@...il.com> To: Jesse Gross <jesse@...ira.com> Cc: David Miller <davem@...emloft.net>, netdev <netdev@...r.kernel.org> Subject: [PATCH net-next-2.6] net: add a recursion limit in xmit path Le mercredi 29 septembre 2010 à 20:43 +0200, Eric Dumazet a écrit : > Le mercredi 29 septembre 2010 à 10:33 -0700, Jesse Gross a écrit : > > > The tx lock has another use here: to break local loops. With this > > change, a misconfigured tunnel can bring down the machine with a stack > > overflow. There are clearly other ways to fix this that don't require > > a lock that restricts parallelism, such as a loop counter, but that's > > the way it is now. > > Thats a very good point ! > > We could use a loop counter in the skb, but this use a bit of ram, > or percpu counters in tunnel drivers, to avoid a given level of > recursion. > > /* this should be shared by all tunnels */ > DEFINE_PER_CPU(tunnel_xmit_count); > > > > tunnel_xmit() > { > if (__this_cpu_read(tunnel_xmit_count) >= LIMIT) > goto tx_error; > __this_cpu_inc(tunnel_xmit_count); > > .... > > __IPTUNNEL_XMIT(tstats, &dev->stats); > > __this_cpu_dec(tunnel_xmit_count), > return NETDEV_TX_OK; > > } > > This can be handled generically in net/core/dev.c David, if you accept the lockless patches, please apply this one before ;) Thanks ! [PATCH net-next-2.6] 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@...ira.com> Signed-off-by: Eric Dumazet <eric.dumazet@...il.com> --- net/core/dev.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/net/core/dev.c b/net/core/dev.c index 48ad47f..50dacca 100644 --- 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); -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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