[PATCH nf] netfilter: nfnetlink_log: wait for rcu grace period before freeing pernet state

[PATCH nf] netfilter: nfnetlink_log: wait for rcu grace period before freeing pernet state

[Florian Westphal]

sashiko reports: "nfnl_log_net_exit() calls nf_log_unset(), which
clears the logger pointer without an RCU grace period.  Immediately after,
ops_free_list() frees the per-net state while concurrent packets might
still be executing nf_log_packet() under rcu_read_lock()."

Clear the pointer via .pre_exit to make sure rcu readers have completed
before pernet storage is free'd.  The change in nf_log_syslog.c is only
done for consistency: it doesn't use pernet data.

Link: https://sashiko.dev/#/patchset/20260731151806.849724-1-pablo%40netfilter.org
Signed-off-by: Florian Westphal <fw@strlen.de>
---
 net/netfilter/nf_log_syslog.c |  4 ++--
 net/netfilter/nfnetlink_log.c | 13 +++++++++----
 2 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/net/netfilter/nf_log_syslog.c b/net/netfilter/nf_log_syslog.c
index e37b09b3203b..5ffde27d450a 100644
--- a/net/netfilter/nf_log_syslog.c
+++ b/net/netfilter/nf_log_syslog.c
@@ -1014,7 +1014,7 @@ static int __net_init nf_log_syslog_net_init(struct net *net)
 	return ret;
 }
 
-static void __net_exit nf_log_syslog_net_exit(struct net *net)
+static void __net_exit nf_log_syslog_net_pre_exit(struct net *net)
 {
 	nf_log_unset(net, &nf_ip_logger);
 	nf_log_unset(net, &nf_arp_logger);
@@ -1025,7 +1025,7 @@ static void __net_exit nf_log_syslog_net_exit(struct net *net)
 
 static struct pernet_operations nf_log_syslog_net_ops = {
 	.init = nf_log_syslog_net_init,
-	.exit = nf_log_syslog_net_exit,
+	.pre_exit = nf_log_syslog_net_pre_exit,
 };
 
 static int __init nf_log_syslog_init(void)
diff --git a/net/netfilter/nfnetlink_log.c b/net/netfilter/nfnetlink_log.c
index 5fee61b3813c..6c7fa2ed34f5 100644
--- a/net/netfilter/nfnetlink_log.c
+++ b/net/netfilter/nfnetlink_log.c
@@ -1170,21 +1170,26 @@ static int __net_init nfnl_log_net_init(struct net *net)
 	return 0;
 }
 
-static void __net_exit nfnl_log_net_exit(struct net *net)
+static void __net_exit nfnl_log_net_pre_exit(struct net *net)
 {
-	struct nfnl_log_net *log = nfnl_log_pernet(net);
-	unsigned int i;
-
 #ifdef CONFIG_PROC_FS
 	remove_proc_entry("nfnetlink_log", net->nf.proc_netfilter);
 #endif
 	nf_log_unset(net, &nfulnl_logger);
+}
+
+static void __net_exit nfnl_log_net_exit(struct net *net)
+{
+	struct nfnl_log_net *log = nfnl_log_pernet(net);
+	unsigned int i;
+
 	for (i = 0; i < INSTANCE_BUCKETS; i++)
 		WARN_ON_ONCE(!hlist_empty(&log->instance_table[i]));
 }
 
 static struct pernet_operations nfnl_log_net_ops = {
 	.init	= nfnl_log_net_init,
+	.pre_exit = nfnl_log_net_pre_exit,
 	.exit	= nfnl_log_net_exit,
 	.id	= &nfnl_log_net_id,
 	.size	= sizeof(struct nfnl_log_net),
-- 
2.54.0

Re: [PATCH nf] netfilter: nfnetlink_log: wait for rcu grace period before freeing pernet state

[Florian Westphal]

Florian Westphal <fw@strlen.de> wrote:
> sashiko reports: "nfnl_log_net_exit() calls nf_log_unset(), which
> clears the logger pointer without an RCU grace period.  Immediately after,
> ops_free_list() frees the per-net state while concurrent packets might
> still be executing nf_log_packet() under rcu_read_lock()."
> 
> Clear the pointer via .pre_exit to make sure rcu readers have completed
> before pernet storage is free'd.  The change in nf_log_syslog.c is only
> done for consistency: it doesn't use pernet data.

Forgot to add:
Fixes: 9368a53c471b ("netfilter: nfnetlink_log: add net namespace support for nfnetlink_log")

The sashiko review can be ignored, its correct but there is a pending
ebt_nflog patch that resolves the issue.