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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>
This commit is contained in:
Brian Haley 2023-01-30 12:14:28 -05:00 committed by Jakub Kicinski
parent 983f507c30
commit 62e395f82d
2 changed files with 20 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
Documentation/networking/ip-sysctl.rst
View File

@ -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.

14
net/core/neighbour.c
View File

@ -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);