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neighbor: fix proxy_delay usage when it is zero
When set to zero, the neighbor sysctl proxy_delay value does not cause an immediate reply for ARP/ND requests as expected, it instead causes a random delay between [0, U32_MAX). Looking at this comment from __get_random_u32_below() explains the reason: /* * This function is technically undefined for ceil == 0, and in fact * for the non-underscored constant version in the header, we build bug * on that. But for the non-constant case, it's convenient to have that * evaluate to being a straight call to get_random_u32(), so that * get_random_u32_inclusive() can work over its whole range without * undefined behavior. */ Added helper function that does not call get_random_u32_below() if proxy_delay is zero and just uses the current value of jiffies instead, causing pneigh_enqueue() to respond immediately. Also added definition of proxy_delay to ip-sysctl.txt since it was missing. Signed-off-by: Brian Haley <haleyb.dev@gmail.com> Link: https://lore.kernel.org/r/20230130171428.367111-1-haleyb.dev@gmail.com Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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@ -1592,6 +1592,14 @@ proxy_arp_pvlan - BOOLEAN
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Hewlett-Packard call it Source-Port filtering or port-isolation.
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Ericsson call it MAC-Forced Forwarding (RFC Draft).
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proxy_delay - INTEGER
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Delay proxy response.
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Delay response to a neighbor solicitation when proxy_arp
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or proxy_ndp is enabled. A random value between [0, proxy_delay)
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will be chosen, setting to zero means reply with no delay.
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Value in jiffies. Defaults to 80.
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shared_media - BOOLEAN
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Send(router) or accept(host) RFC1620 shared media redirects.
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Overrides secure_redirects.
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@ -1662,11 +1662,21 @@ static void neigh_proxy_process(struct timer_list *t)
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spin_unlock(&tbl->proxy_queue.lock);
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}
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static unsigned long neigh_proxy_delay(struct neigh_parms *p)
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{
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/* If proxy_delay is zero, do not call get_random_u32_below()
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* as it is undefined behavior.
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*/
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unsigned long proxy_delay = NEIGH_VAR(p, PROXY_DELAY);
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return proxy_delay ?
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jiffies + get_random_u32_below(proxy_delay) : jiffies;
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}
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void pneigh_enqueue(struct neigh_table *tbl, struct neigh_parms *p,
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struct sk_buff *skb)
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{
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unsigned long sched_next = jiffies +
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get_random_u32_below(NEIGH_VAR(p, PROXY_DELAY));
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unsigned long sched_next = neigh_proxy_delay(p);
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if (p->qlen > NEIGH_VAR(p, PROXY_QLEN)) {
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kfree_skb(skb);
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