Commit 62e395f8 authored by Brian Haley's avatar Brian Haley Committed by Jakub Kicinski
Browse files

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: default avatarBrian Haley <haleyb.dev@gmail.com>
Link: https://lore.kernel.org/r/20230130171428.367111-1-haleyb.dev@gmail.com


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent 983f507c

Documentation/networking/ip-sysctl.rst

+8 −0
Original line number Diff line number Diff line
@@ -1592,6 +1592,14 @@ proxy_arp_pvlan - BOOLEAN 
	  Hewlett-Packard call it Source-Port filtering or port-isolation.

	  Ericsson call it MAC-Forced Forwarding (RFC Draft).



proxy_delay - INTEGER

	Delay proxy response.



	Delay response to a neighbor solicitation when proxy_arp

	or proxy_ndp is enabled. A random value between [0, proxy_delay)

	will be chosen, setting to zero means reply with no delay.

	Value in jiffies. Defaults to 80.



shared_media - BOOLEAN

	Send(router) or accept(host) RFC1620 shared media redirects.

	Overrides secure_redirects.

net/core/neighbour.c

+12 −2
Original line number Diff line number Diff line
@@ -1662,11 +1662,21 @@ static void neigh_proxy_process(struct timer_list *t) 
	spin_unlock(&tbl->proxy_queue.lock);

}



static unsigned long neigh_proxy_delay(struct neigh_parms *p)

{

	/* If proxy_delay is zero, do not call get_random_u32_below()

	 * as it is undefined behavior.

	 */

	unsigned long proxy_delay = NEIGH_VAR(p, PROXY_DELAY);



	return proxy_delay ?

	       jiffies + get_random_u32_below(proxy_delay) : jiffies;

}



void pneigh_enqueue(struct neigh_table *tbl, struct neigh_parms *p,

		    struct sk_buff *skb)

{

	unsigned long sched_next = jiffies +

			get_random_u32_below(NEIGH_VAR(p, PROXY_DELAY));

	unsigned long sched_next = neigh_proxy_delay(p);



	if (p->qlen > NEIGH_VAR(p, PROXY_QLEN)) {

		kfree_skb(skb);