commit f13f2aeed154da8e48f90b85e720f8ba39b1e881
author Philip Whineray <phil@firehol.org> Sun Nov 22 11:35:07 2015 +0000
committer Pablo Neira Ayuso <pablo@netfilter.org> Wed Nov 25 13:54:09 2015 +0100
tree 3e7035ef8a97bcc475381fb7c5227e087e45a70a
parent daaa7d647f81f3f1494d9a9029d611b666d63181

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>

net/netfilter/x_tables.c

diff --git a/net/netfilter/x_tables.c b/net/netfilter/x_tables.c
index d4aaad7..c8a0b7d 100644
--- a/net/netfilter/x_tables.c
+++ b/net/netfilter/x_tables.c
@@ -26,6 +26,7 @@
 #include <linux/mm.h>
 #include <linux/slab.h>
 #include <linux/audit.h>
+#include <linux/user_namespace.h>
 #include <net/net_namespace.h>
 
 #include <linux/netfilter/x_tables.h>
@@ -1226,6 +1227,8 @@
 #ifdef CONFIG_PROC_FS
 	char buf[XT_FUNCTION_MAXNAMELEN];
 	struct proc_dir_entry *proc;
+	kuid_t root_uid;
+	kgid_t root_gid;
 #endif
 
 	if (af >= ARRAY_SIZE(xt_prefix))
@@ -1233,12 +1236,17 @@
 
 
 #ifdef CONFIG_PROC_FS
+	root_uid = make_kuid(net->user_ns, 0);
+	root_gid = make_kgid(net->user_ns, 0);
+
 	strlcpy(buf, xt_prefix[af], sizeof(buf));
 	strlcat(buf, FORMAT_TABLES, sizeof(buf));
 	proc = proc_create_data(buf, 0440, net->proc_net, &xt_table_ops,
 				(void *)(unsigned long)af);
 	if (!proc)
 		goto out;
+	if (uid_valid(root_uid) && gid_valid(root_gid))
+		proc_set_user(proc, root_uid, root_gid);
 
 	strlcpy(buf, xt_prefix[af], sizeof(buf));
 	strlcat(buf, FORMAT_MATCHES, sizeof(buf));
@@ -1246,6 +1254,8 @@
 				(void *)(unsigned long)af);
 	if (!proc)
 		goto out_remove_tables;
+	if (uid_valid(root_uid) && gid_valid(root_gid))
+		proc_set_user(proc, root_uid, root_gid);
 
 	strlcpy(buf, xt_prefix[af], sizeof(buf));
 	strlcat(buf, FORMAT_TARGETS, sizeof(buf));
@@ -1253,6 +1263,8 @@
 				(void *)(unsigned long)af);
 	if (!proc)
 		goto out_remove_matches;
+	if (uid_valid(root_uid) && gid_valid(root_gid))
+		proc_set_user(proc, root_uid, root_gid);
 #endif
 
 	return 0;