netfilter: Set /proc/net entries owner to root in namespace

Various files are owned by root with 0440 permission. Reading them is
impossible in an unprivileged user namespace, interfering with firewall
tools. For instance, iptables-save relies on /proc/net/ip_tables_names
contents to dump only loaded tables.

This patch assigned ownership of the following files to root in the
current namespace:

- /proc/net/*_tables_names
- /proc/net/*_tables_matches
- /proc/net/*_tables_targets
- /proc/net/nf_conntrack
- /proc/net/nf_conntrack_expect
- /proc/net/netfilter/nfnetlink_log

A mapping for root must be available, so this order should be followed:

unshare(CLONE_NEWUSER);
/* Setup the mapping */
unshare(CLONE_NEWNET);

Signed-off-by: Philip Whineray <phil@firehol.org>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 7 insertions, 0 deletions

diff --git a/net/netfilter/nf_conntrack_standalone.c b/net/netfilter/nf_conntrack_standalone.c
index 1fb3cacc04e167..0f1a45bcacb241 100644
--- a/net/netfilter/nf_conntrack_standalone.c
+++ b/net/netfilter/nf_conntrack_standalone.c
@@ -392,11 +392,18 @@ static const struct file_operations ct_cpu_seq_fops = {
 static int nf_conntrack_standalone_init_proc(struct net *net)
 {
 	struct proc_dir_entry *pde;
+	kuid_t root_uid;
+	kgid_t root_gid;
 
 	pde = proc_create("nf_conntrack", 0440, net->proc_net, &ct_file_ops);
 	if (!pde)
 		goto out_nf_conntrack;
 
+	root_uid = make_kuid(net->user_ns, 0);
+	root_gid = make_kgid(net->user_ns, 0);
+	if (uid_valid(root_uid) && gid_valid(root_gid))
+		proc_set_user(pde, root_uid, root_gid);
+
 	pde = proc_create("nf_conntrack", S_IRUGO, net->proc_net_stat,
 			  &ct_cpu_seq_fops);
 	if (!pde)