netdev - [PATCH net-next 2/2] netfilter: conntrack: Make global sysctls readonly in non-init netns

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Date:   Mon, 12 Apr 2021 00:24:53 -0400
From:   Jonathon Reinhart <jonathon.reinhart@...il.com>
To:     netdev@...r.kernel.org
Cc:     Jonathon Reinhart <Jonathon.Reinhart@...il.com>,
        Florian Westphal <fw@...len.de>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH net-next 2/2] netfilter: conntrack: Make global sysctls readonly in non-init netns

These sysctls point to global variables:
- NF_SYSCTL_CT_MAX (&nf_conntrack_max)
- NF_SYSCTL_CT_EXPECT_MAX (&nf_ct_expect_max)
- NF_SYSCTL_CT_BUCKETS (&nf_conntrack_htable_size_user)

Because their data pointers are not updated to point to per-netns
structures, they must be marked read-only in a non-init_net ns.
Otherwise, changes in any net namespace are reflected in (leaked into)
all other net namespaces. This problem has existed since the
introduction of net namespaces.

The current logic marks them read-only only if the net namespace is
owned by an unprivileged user (other than init_user_ns).

Commit d0febd81ae77 ("netfilter: conntrack: re-visit sysctls in
unprivileged namespaces") "exposes all sysctls even if the namespace is
unpriviliged." Since we need to mark them readonly in any case, we can
forego the unprivileged user check altogether.

Fixes: d0febd81ae77 ("netfilter: conntrack: re-visit sysctls in unprivileged namespaces")
Signed-off-by: Jonathon Reinhart <Jonathon.Reinhart@...il.com>
---
 net/netfilter/nf_conntrack_standalone.c | 10 ++--------
 1 file changed, 2 insertions(+), 8 deletions(-)

diff --git a/net/netfilter/nf_conntrack_standalone.c b/net/netfilter/nf_conntrack_standalone.c
index 3f2cc7b04b20..54d36d3eb905 100644
--- a/net/netfilter/nf_conntrack_standalone.c
+++ b/net/netfilter/nf_conntrack_standalone.c
@@ -1060,16 +1060,10 @@ static int nf_conntrack_standalone_init_sysctl(struct net *net)
 	nf_conntrack_standalone_init_dccp_sysctl(net, table);
 	nf_conntrack_standalone_init_gre_sysctl(net, table);
 
-	/* Don't allow unprivileged users to alter certain sysctls */
-	if (net->user_ns != &init_user_ns) {
+	/* Don't allow non-init_net ns to alter global sysctls */
+	if (!net_eq(&init_net, net)) {
 		table[NF_SYSCTL_CT_MAX].mode = 0444;
 		table[NF_SYSCTL_CT_EXPECT_MAX].mode = 0444;
-		table[NF_SYSCTL_CT_HELPER].mode = 0444;
-#ifdef CONFIG_NF_CONNTRACK_EVENTS
-		table[NF_SYSCTL_CT_EVENTS].mode = 0444;
-#endif
-		table[NF_SYSCTL_CT_BUCKETS].mode = 0444;
-	} else if (!net_eq(&init_net, net)) {
 		table[NF_SYSCTL_CT_BUCKETS].mode = 0444;
 	}
 
-- 
2.20.1