netdev - [PATCH] l2tp: Allow management of tunnels and session in user namespace

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Message-Id: <20200407111148.28406-1-michael.weiss@aisec.fraunhofer.de>
Date:   Tue,  7 Apr 2020 13:11:48 +0200
From:   Michael Weiß <michael.weiss@...ec.fraunhofer.de>
To:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     netdev@...r.kernel.org,
        Michael Weiß <michael.weiss@...ec.fraunhofer.de>
Subject: [PATCH] l2tp: Allow management of tunnels and session in user namespace

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@...ec.fraunhofer.de>
---
 net/l2tp/l2tp_netlink.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/net/l2tp/l2tp_netlink.c b/net/l2tp/l2tp_netlink.c
index f5a9bdc4980c..ebb381c3f1b9 100644
--- a/net/l2tp/l2tp_netlink.c
+++ b/net/l2tp/l2tp_netlink.c
@@ -920,51 +920,51 @@ static const struct genl_ops l2tp_nl_ops[] = {
 		.cmd = L2TP_CMD_TUNNEL_CREATE,
 		.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
 		.doit = l2tp_nl_cmd_tunnel_create,
-		.flags = GENL_ADMIN_PERM,
+		.flags = GENL_UNS_ADMIN_PERM,
 	},
 	{
 		.cmd = L2TP_CMD_TUNNEL_DELETE,
 		.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
 		.doit = l2tp_nl_cmd_tunnel_delete,
-		.flags = GENL_ADMIN_PERM,
+		.flags = GENL_UNS_ADMIN_PERM,
 	},
 	{
 		.cmd = L2TP_CMD_TUNNEL_MODIFY,
 		.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
 		.doit = l2tp_nl_cmd_tunnel_modify,
-		.flags = GENL_ADMIN_PERM,
+		.flags = GENL_UNS_ADMIN_PERM,
 	},
 	{
 		.cmd = L2TP_CMD_TUNNEL_GET,
 		.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
 		.doit = l2tp_nl_cmd_tunnel_get,
 		.dumpit = l2tp_nl_cmd_tunnel_dump,
-		.flags = GENL_ADMIN_PERM,
+		.flags = GENL_UNS_ADMIN_PERM,
 	},
 	{
 		.cmd = L2TP_CMD_SESSION_CREATE,
 		.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
 		.doit = l2tp_nl_cmd_session_create,
-		.flags = GENL_ADMIN_PERM,
+		.flags = GENL_UNS_ADMIN_PERM,
 	},
 	{
 		.cmd = L2TP_CMD_SESSION_DELETE,
 		.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
 		.doit = l2tp_nl_cmd_session_delete,
-		.flags = GENL_ADMIN_PERM,
+		.flags = GENL_UNS_ADMIN_PERM,
 	},
 	{
 		.cmd = L2TP_CMD_SESSION_MODIFY,
 		.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
 		.doit = l2tp_nl_cmd_session_modify,
-		.flags = GENL_ADMIN_PERM,
+		.flags = GENL_UNS_ADMIN_PERM,
 	},
 	{
 		.cmd = L2TP_CMD_SESSION_GET,
 		.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
 		.doit = l2tp_nl_cmd_session_get,
 		.dumpit = l2tp_nl_cmd_session_dump,
-		.flags = GENL_ADMIN_PERM,
+		.flags = GENL_UNS_ADMIN_PERM,
 	},
 };
 
-- 
2.20.1