[PATCH net 2/9] netfilter: ecache: fix inverted time_after() check

[Florian Westphal <fw@strlen.de>]

From: Yizhou Zhao <zhaoyz24@mails.tsinghua.edu.cn>

ecache_work_evict_list() redelivers DESTROY events for conntracks that
were moved to the per-netns dying_list after event delivery failed.  It
sets a 10ms deadline:

    stop = jiffies + ECACHE_MAX_JIFFIES

but then tests:

    time_after(stop, jiffies)

This condition is true while the deadline is still in the future, so the
worker returns STATE_RESTART after the first successful redelivery in the
usual case.  ecache_work() maps STATE_RESTART to delay 0, which turns the
redelivery path into one dying conntrack per workqueue dispatch and makes
the sent > 16 batching/cond_resched() path effectively unreachable.

A conntrack netlink listener whose receive queue is congested can make
DESTROY event delivery fail with -ENOBUFS.  With sustained conntrack
churn, entries then accumulate on the dying_list and are only drained at
the degraded one-entry-per-dispatch rate once delivery succeeds again,
wasting CPU on back-to-back workqueue reschedules and prolonging
conntrack memory/resource pressure.

In a KASAN QEMU test with CONFIG_NF_CONNTRACK_EVENTS=y and
nf_conntrack.enable_hooks=1, a congested DESTROY listener caused 8192
nf_ct_delete() calls to return false and move entries to the dying_list.
After closing the listener, the unfixed kernel needed 7670 ecache_work()
entries to destroy 7669 conntracks.  With this change, the same 8192
entries were destroyed by 2 ecache_work() entries.

Swap the comparison so the worker restarts only after the deadline has
expired.

Fixes: 2ed3bf188b33 ("netfilter: ecache: use dedicated list for event redelivery")
Cc: stable@vger.kernel.org
Reported-by: Yizhou Zhao <zhaoyz24@mails.tsinghua.edu.cn>
Reported-by: Yuxiang Yang <yangyx22@mails.tsinghua.edu.cn>
Reported-by: Ao Wang <wangao@seu.edu.cn>
Reported-by: Xuewei Feng <fengxw06@126.com>
Reported-by: Qi Li <qli01@tsinghua.edu.cn>
Reported-by: Ke Xu <xuke@tsinghua.edu.cn>
Assisted-by: Claude-Code:GLM-5.2
Signed-off-by: Yizhou Zhao <zhaoyz24@mails.tsinghua.edu.cn>
Signed-off-by: Florian Westphal <fw@strlen.de>
---
 net/netfilter/nf_conntrack_ecache.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/netfilter/nf_conntrack_ecache.c b/net/netfilter/nf_conntrack_ecache.c
index 9df159448b89..cc8d8e85169f 100644
--- a/net/netfilter/nf_conntrack_ecache.c
+++ b/net/netfilter/nf_conntrack_ecache.c
@@ -77,7 +77,7 @@ static enum retry_state ecache_work_evict_list(struct nf_conntrack_net *cnet)
 		hlist_nulls_del_rcu(&ct->tuplehash[IP_CT_DIR_ORIGINAL].hnnode);
 		hlist_nulls_add_head(&ct->tuplehash[IP_CT_DIR_REPLY].hnnode, &evicted_list);
 
-		if (time_after(stop, jiffies)) {
+		if (time_after(jiffies, stop)) {
 			ret = STATE_RESTART;
 			break;
 		}
-- 
2.54.0