[PATCH AUTOSEL 6.2 31/53] neighbor: fix proxy_delay usage when it is zero

Sasha Levin
2023-02-26T14:48:23Z

From: Brian Haley <haleyb.dev@gmail.com>

[ 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@gmail.com>
Link: https://lore.kernel.org/r/20230130171428.367111-1-haleyb.dev@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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