mptcp: allow privileged operations from user namespaces

GENL_ADMIN_PERM checks that the user has CAP_NET_ADMIN in the initial
namespace by calling netlink_capable(). Instead, use GENL_UNS_ADMIN_PERM
which uses netlink_ns_capable(). This checks that the caller has
CAP_NET_ADMIN in the current user namespace.

See also

  commit 4a92602a ("openvswitch: allow management from inside user namespaces")

which introduced this mechanism. See also

  commit 5617c6cd ("nl80211: Allow privileged operations from user namespaces")

which introduced this for nl80211.
Signed-off-by: Thomas Haller <thaller@redhat.com>
Reviewed-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

net/mptcp/pm_netlink.c

@@ -2218,17 +2218,17 @@ static const struct genl_small_ops mptcp_pm_ops[] = {
 	{
 		.cmd    = MPTCP_PM_CMD_ADD_ADDR,
 		.doit   = mptcp_nl_cmd_add_addr,
-		.flags  = GENL_ADMIN_PERM,
+		.flags  = GENL_UNS_ADMIN_PERM,
 	},
 	{
 		.cmd    = MPTCP_PM_CMD_DEL_ADDR,
 		.doit   = mptcp_nl_cmd_del_addr,
-		.flags  = GENL_ADMIN_PERM,
+		.flags  = GENL_UNS_ADMIN_PERM,
 	},
 	{
 		.cmd    = MPTCP_PM_CMD_FLUSH_ADDRS,
 		.doit   = mptcp_nl_cmd_flush_addrs,
-		.flags  = GENL_ADMIN_PERM,
+		.flags  = GENL_UNS_ADMIN_PERM,
 	},
 	{
 		.cmd    = MPTCP_PM_CMD_GET_ADDR,
@@ -2238,7 +2238,7 @@ static const struct genl_small_ops mptcp_pm_ops[] = {
 	{
 		.cmd    = MPTCP_PM_CMD_SET_LIMITS,
 		.doit   = mptcp_nl_cmd_set_limits,
-		.flags  = GENL_ADMIN_PERM,
+		.flags  = GENL_UNS_ADMIN_PERM,
 	},
 	{
 		.cmd    = MPTCP_PM_CMD_GET_LIMITS,
@@ -2247,27 +2247,27 @@ static const struct genl_small_ops mptcp_pm_ops[] = {
 	{
 		.cmd    = MPTCP_PM_CMD_SET_FLAGS,
 		.doit   = mptcp_nl_cmd_set_flags,
-		.flags  = GENL_ADMIN_PERM,
+		.flags  = GENL_UNS_ADMIN_PERM,
 	},
 	{
 		.cmd    = MPTCP_PM_CMD_ANNOUNCE,
 		.doit   = mptcp_nl_cmd_announce,
-		.flags  = GENL_ADMIN_PERM,
+		.flags  = GENL_UNS_ADMIN_PERM,
 	},
 	{
 		.cmd    = MPTCP_PM_CMD_REMOVE,
 		.doit   = mptcp_nl_cmd_remove,
-		.flags  = GENL_ADMIN_PERM,
+		.flags  = GENL_UNS_ADMIN_PERM,
 	},
 	{
 		.cmd    = MPTCP_PM_CMD_SUBFLOW_CREATE,
 		.doit   = mptcp_nl_cmd_sf_create,
-		.flags  = GENL_ADMIN_PERM,
+		.flags  = GENL_UNS_ADMIN_PERM,
 	},
 	{
 		.cmd    = MPTCP_PM_CMD_SUBFLOW_DESTROY,
 		.doit   = mptcp_nl_cmd_sf_destroy,
-		.flags  = GENL_ADMIN_PERM,
+		.flags  = GENL_UNS_ADMIN_PERM,
 	},
 };