netdev - [PATCH net] netfilter: conntrack: fix reading nf_conntrack

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Date:   Fri, 08 Jan 2021 12:44:33 +0100
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     Pablo Neira Ayuso <pablo@...filter.org>,
        netfilter-devel@...r.kernel.org
Cc:     Jesper Dangaard Brouer <brouer@...hat.com>,
        Florian Westphal <fw@...len.de>, netdev@...r.kernel.org
Subject: [PATCH net] netfilter: conntrack: fix reading nf_conntrack_buckets

The old way of changing the conntrack hashsize runtime was through changing
the module param via file /sys/module/nf_conntrack/parameters/hashsize. This
was extended to sysctl change in commit 3183ab8997a4 ("netfilter: conntrack:
allow increasing bucket size via sysctl too").

The commit introduced second "user" variable nf_conntrack_htable_size_user
which shadow actual variable nf_conntrack_htable_size. When hashsize is
changed via module param this "user" variable isn't updated. This results in
sysctl net/netfilter/nf_conntrack_buckets shows the wrong value when users
update via the old way.

This patch fix the issue by always updating "user" variable when reading the
proc file. This will take care of changes to the actual variable without
sysctl need to be aware.

Fixes: 3183ab8997a4 ("netfilter: conntrack: allow increasing bucket size via sysctl too")
Reported-by: Yoel Caspersen <yoel@...knet.dk>
Signed-off-by: Jesper Dangaard Brouer <brouer@...hat.com>
---
 net/netfilter/nf_conntrack_standalone.c |    3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/netfilter/nf_conntrack_standalone.c b/net/netfilter/nf_conntrack_standalone.c
index 46c5557c1fec..0ee702d374b0 100644
--- a/net/netfilter/nf_conntrack_standalone.c
+++ b/net/netfilter/nf_conntrack_standalone.c
@@ -523,6 +523,9 @@ nf_conntrack_hash_sysctl(struct ctl_table *table, int write,
 {
 	int ret;

+	/* module_param hashsize could have changed value */
+	nf_conntrack_htable_size_user = nf_conntrack_htable_size;
+
 	ret = proc_dointvec(table, write, buffer, lenp, ppos);
 	if (ret < 0 || !write)
 		return ret;