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Commit 1eec5d56 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

inet: frags: do not clone skb in ip_expire() 



An skb_clone() was added in commit ec4fbd64 ("inet: frag: release
spinlock before calling icmp_send()")

While fixing the bug at that time, it also added a very high cost
for DDOS frags, as the ICMP rate limit is applied after this
expensive operation (skb_clone() + consume_skb(), implying memory
allocations, copy, and freeing)

We can use skb_get(head) here, all we want is to make sure skb wont
be freed by another cpu.

Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 3e67f106

net/ipv4/ip_fragment.c

+6 −10
Original line number Diff line number Diff line
@@ -143,8 +143,8 @@ static bool frag_expire_skip_icmp(u32 user) 
static void ip_expire(struct timer_list *t)

{

	struct inet_frag_queue *frag = from_timer(frag, t, timer);

	struct sk_buff *clone, *head;

	const struct iphdr *iph;

	struct sk_buff *head;

	struct net *net;

	struct ipq *qp;

	int err;
@@ -187,16 +187,12 @@ static void ip_expire(struct timer_list *t) 
	    (skb_rtable(head)->rt_type != RTN_LOCAL))

		goto out;



	clone = skb_clone(head, GFP_ATOMIC);



	/* Send an ICMP "Fragment Reassembly Timeout" message. */

	if (clone) {

	skb_get(head);

	spin_unlock(&qp->q.lock);

		icmp_send(clone, ICMP_TIME_EXCEEDED,

			  ICMP_EXC_FRAGTIME, 0);

		consume_skb(clone);

	icmp_send(head, ICMP_TIME_EXCEEDED, ICMP_EXC_FRAGTIME, 0);

	kfree_skb(head);

	goto out_rcu_unlock;

	}



out:

	spin_unlock(&qp->q.lock);

out_rcu_unlock: