[PATCH] netfilter: don't permit unprivileged writes to global state via sysctls

This prevents the modification of nf_conntrack_max in unprivileged network
namespaces. For unprivileged network namespaces, ip_conntrack_max is kept
as a readonly sysctl in order to minimize potential compatibility issues.

This patch should apply cleanly to the net tree.

Signed-off-by: Jann Horn <redacted>
---
 net/ipv4/netfilter/nf_conntrack_l3proto_ipv4.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/ipv4/netfilter/nf_conntrack_l3proto_ipv4.c b/net/ipv4/netfilter/nf_conntrack_l3proto_ipv4.c
index ae1a71a..a639e94 100644
--- a/net/ipv4/netfilter/nf_conntrack_l3proto_ipv4.c
+++ b/net/ipv4/netfilter/nf_conntrack_l3proto_ipv4.c

@@ -358,6 +358,9 @@ static int ipv4_init_net(struct net *net)
 	if (!in->ctl_table)
 		return -ENOMEM;
 
+	if (net->user_ns != &init_user_ns)
+		in->ctl_table[0].mode = 0444;
+
 	in->ctl_table[0].data = &nf_conntrack_max;
 	in->ctl_table[1].data = &net->ct.count;
 	in->ctl_table[2].data = &nf_conntrack_htable_size;

-- 
2.1.4