[PATCH 5.11 02/31] netfilter: conntrack: Make global sysctls readonly in non-init netns

From: Greg Kroah-Hartman
Date: Wed May 05 2021 - 08:11:41 EST

From: Jonathon Reinhart <jonathon.reinhart@xxxxxxxxx>

commit 2671fa4dc0109d3fb581bc3078fdf17b5d9080f6 upstream.

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@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
net/netfilter/nf_conntrack_standalone.c | 10 ++--------
1 file changed, 2 insertions(+), 8 deletions(-)

--- a/net/netfilter/nf_conntrack_standalone.c
+++ b/net/netfilter/nf_conntrack_standalone.c
@@ -1060,16 +1060,10 @@ static int nf_conntrack_standalone_init_
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;
- table[NF_SYSCTL_CT_EVENTS].mode = 0444;
- table[NF_SYSCTL_CT_BUCKETS].mode = 0444;
- } else if (!net_eq(&init_net, net)) {
table[NF_SYSCTL_CT_BUCKETS].mode = 0444;