From: =?UTF-8?q?Michael=20Wei=C3=9F?= <michael.weiss@aisec.fraunhofer.de>
Date: Tue, 7 Apr 2020 13:11:48 +0200
Subject: l2tp: Allow management of tunnels and session in user namespace
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Git-commit: 2abe05234f2e892728c388169631e4b99f354c86
Patch-mainline: 5.7-rc2
References: networking-stable-20_04_17

Creation and management of L2TPv3 tunnels and session through netlink
requires CAP_NET_ADMIN. However, a process with CAP_NET_ADMIN in a
non-initial user namespace gets an EPERM due to the use of the
genetlink GENL_ADMIN_PERM flag. Thus, management of L2TP VPNs inside
an unprivileged container won't work.

We replaced the GENL_ADMIN_PERM by the GENL_UNS_ADMIN_PERM flag
similar to other network modules which also had this problem, e.g.,
openvswitch (commit 4a92602aa1cd "openvswitch: allow management from
inside user namespaces") and nl80211 (commit 5617c6cd6f844 "nl80211:
Allow privileged operations from user namespaces").

I tested this in the container runtime trustm3 (trustm3.github.io)
and was able to create l2tp tunnels and sessions in unpriviliged
(user namespaced) containers using a private network namespace.
For other runtimes such as docker or lxc this should work, too.

Signed-off-by: Michael Weiß <michael.weiss@aisec.fraunhofer.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 net/l2tp/l2tp_netlink.c |   16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

--- a/net/l2tp/l2tp_netlink.c
+++ b/net/l2tp/l2tp_netlink.c
@@ -958,51 +958,51 @@ static const struct genl_ops l2tp_nl_ops
 		.cmd = L2TP_CMD_TUNNEL_CREATE,
 		.doit = l2tp_nl_cmd_tunnel_create,
 		.policy = l2tp_nl_policy,
-		.flags = GENL_ADMIN_PERM,
+		.flags = GENL_UNS_ADMIN_PERM,
 	},
 	{
 		.cmd = L2TP_CMD_TUNNEL_DELETE,
 		.doit = l2tp_nl_cmd_tunnel_delete,
 		.policy = l2tp_nl_policy,
-		.flags = GENL_ADMIN_PERM,
+		.flags = GENL_UNS_ADMIN_PERM,
 	},
 	{
 		.cmd = L2TP_CMD_TUNNEL_MODIFY,
 		.doit = l2tp_nl_cmd_tunnel_modify,
 		.policy = l2tp_nl_policy,
-		.flags = GENL_ADMIN_PERM,
+		.flags = GENL_UNS_ADMIN_PERM,
 	},
 	{
 		.cmd = L2TP_CMD_TUNNEL_GET,
 		.doit = l2tp_nl_cmd_tunnel_get,
 		.dumpit = l2tp_nl_cmd_tunnel_dump,
 		.policy = l2tp_nl_policy,
-		.flags = GENL_ADMIN_PERM,
+		.flags = GENL_UNS_ADMIN_PERM,
 	},
 	{
 		.cmd = L2TP_CMD_SESSION_CREATE,
 		.doit = l2tp_nl_cmd_session_create,
 		.policy = l2tp_nl_policy,
-		.flags = GENL_ADMIN_PERM,
+		.flags = GENL_UNS_ADMIN_PERM,
 	},
 	{
 		.cmd = L2TP_CMD_SESSION_DELETE,
 		.doit = l2tp_nl_cmd_session_delete,
 		.policy = l2tp_nl_policy,
-		.flags = GENL_ADMIN_PERM,
+		.flags = GENL_UNS_ADMIN_PERM,
 	},
 	{
 		.cmd = L2TP_CMD_SESSION_MODIFY,
 		.doit = l2tp_nl_cmd_session_modify,
 		.policy = l2tp_nl_policy,
-		.flags = GENL_ADMIN_PERM,
+		.flags = GENL_UNS_ADMIN_PERM,
 	},
 	{
 		.cmd = L2TP_CMD_SESSION_GET,
 		.doit = l2tp_nl_cmd_session_get,
 		.dumpit = l2tp_nl_cmd_session_dump,
 		.policy = l2tp_nl_policy,
-		.flags = GENL_ADMIN_PERM,
+		.flags = GENL_UNS_ADMIN_PERM,
 	},
 };