From: Brian Haley <haleyb.dev@xxxxxxxxx> [ Upstream commit 62e395f82d04510b0f86e5e603e29412be88596f ] 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@xxxxxxxxx> Link: https://lore.kernel.org/r/20230130171428.367111-1-haleyb.dev@xxxxxxxxx Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- Documentation/networking/ip-sysctl.rst | 8 ++++++++ net/core/neighbour.c | 14 ++++++++++++-- 2 files changed, 20 insertions(+), 2 deletions(-) diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst index 7fbd060d60470..f0bf509d2321b 100644 --- a/Documentation/networking/ip-sysctl.rst +++ b/Documentation/networking/ip-sysctl.rst @@ -1589,6 +1589,14 @@ 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. diff --git a/net/core/neighbour.c b/net/core/neighbour.c index 4edd2176e2385..6798f6d2423b9 100644 --- a/net/core/neighbour.c +++ b/net/core/neighbour.c @@ -1674,11 +1674,21 @@ 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); -- 2.39.0
