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

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An skb_clone() was added in commit ec4fbd6475 ("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: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2018-03-31 12:58:54 -07:00 committed by David S. Miller
parent 3e67f106f6
commit 1eec5d5670
1 changed files with 6 additions and 10 deletions
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16
net/ipv4/ip_fragment.c
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@ -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);
skb_get(head);
spin_unlock(&qp->q.lock);
icmp_send(head, ICMP_TIME_EXCEEDED, ICMP_EXC_FRAGTIME, 0);
kfree_skb(head);
goto out_rcu_unlock;
/* Send an ICMP "Fragment Reassembly Timeout" message. */
if (clone) {
spin_unlock(&qp->q.lock);
icmp_send(clone, ICMP_TIME_EXCEEDED,
ICMP_EXC_FRAGTIME, 0);
consume_skb(clone);
goto out_rcu_unlock;
}
out:
spin_unlock(&qp->q.lock);
out_rcu_unlock: