openvswitch: allow management from inside user namespaces

Operations with the GENL_ADMIN_PERM flag fail permissions checks because
this flag means we call netlink_capable, which uses the init user ns.

Instead, let's introduce a new flag, GENL_UNS_ADMIN_PERM for operations
which should be allowed inside a user namespace.

The motivation for this is to be able to run openvswitch in unprivileged
containers. I've tested this and it seems to work, but I really have no
idea about the security consequences of this patch, so thoughts would be
much appreciated.

v2: use the GENL_UNS_ADMIN_PERM flag instead of a check in each function
v3: use separate ifs for UNS_ADMIN_PERM and ADMIN_PERM, instead of one
    massive one

Reported-by: James Page <james.page@canonical.com>
Signed-off-by: Tycho Andersen <tycho.andersen@canonical.com>
CC: Eric Biederman <ebiederm@xmission.com>
CC: Pravin Shelar <pshelar@ovn.org>
CC: Justin Pettit <jpettit@nicira.com>
CC: "David S. Miller" <davem@davemloft.net>
Acked-by: Pravin B Shelar <pshelar@ovn.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/uapi/linux/genetlink.h

@@ -21,6 +21,7 @@ struct genlmsghdr {
 #define GENL_CMD_CAP_DO		0x02
 #define GENL_CMD_CAP_DUMP	0x04
 #define GENL_CMD_CAP_HASPOL	0x08
+#define GENL_UNS_ADMIN_PERM	0x10
 
 /*
  * List of reserved static generic netlink identifiers:

net/netlink/genetlink.c

@@ -580,6 +580,10 @@ static int genl_family_rcv_msg(struct genl_family *family,
 	    !netlink_capable(skb, CAP_NET_ADMIN))
 		return -EPERM;
 
+	if ((ops->flags & GENL_UNS_ADMIN_PERM) &&
+	    !netlink_ns_capable(skb, net->user_ns, CAP_NET_ADMIN))
+		return -EPERM;
+
 	if ((nlh->nlmsg_flags & NLM_F_DUMP) == NLM_F_DUMP) {
 		int rc;
 

net/openvswitch/datapath.c

@@ -654,7 +654,7 @@ static const struct nla_policy packet_policy[OVS_PACKET_ATTR_MAX + 1] = {
 
 static const struct genl_ops dp_packet_genl_ops[] = {
 	{ .cmd = OVS_PACKET_CMD_EXECUTE,
-	  .flags = GENL_ADMIN_PERM, /* Requires CAP_NET_ADMIN privilege. */
+	  .flags = GENL_UNS_ADMIN_PERM, /* Requires CAP_NET_ADMIN privilege. */
 	  .policy = packet_policy,
 	  .doit = ovs_packet_cmd_execute
 	}
@@ -1391,12 +1391,12 @@ static const struct nla_policy flow_policy[OVS_FLOW_ATTR_MAX + 1] = {
 
 static const struct genl_ops dp_flow_genl_ops[] = {
 	{ .cmd = OVS_FLOW_CMD_NEW,
-	  .flags = GENL_ADMIN_PERM, /* Requires CAP_NET_ADMIN privilege. */
+	  .flags = GENL_UNS_ADMIN_PERM, /* Requires CAP_NET_ADMIN privilege. */
 	  .policy = flow_policy,
 	  .doit = ovs_flow_cmd_new
 	},
 	{ .cmd = OVS_FLOW_CMD_DEL,
-	  .flags = GENL_ADMIN_PERM, /* Requires CAP_NET_ADMIN privilege. */
+	  .flags = GENL_UNS_ADMIN_PERM, /* Requires CAP_NET_ADMIN privilege. */
 	  .policy = flow_policy,
 	  .doit = ovs_flow_cmd_del
 	},
@@ -1407,7 +1407,7 @@ static const struct genl_ops dp_flow_genl_ops[] = {
 	  .dumpit = ovs_flow_cmd_dump
 	},
 	{ .cmd = OVS_FLOW_CMD_SET,
-	  .flags = GENL_ADMIN_PERM, /* Requires CAP_NET_ADMIN privilege. */
+	  .flags = GENL_UNS_ADMIN_PERM, /* Requires CAP_NET_ADMIN privilege. */
 	  .policy = flow_policy,
 	  .doit = ovs_flow_cmd_set,
 	},
@@ -1777,12 +1777,12 @@ static const struct nla_policy datapath_policy[OVS_DP_ATTR_MAX + 1] = {
 
 static const struct genl_ops dp_datapath_genl_ops[] = {
 	{ .cmd = OVS_DP_CMD_NEW,
-	  .flags = GENL_ADMIN_PERM, /* Requires CAP_NET_ADMIN privilege. */
+	  .flags = GENL_UNS_ADMIN_PERM, /* Requires CAP_NET_ADMIN privilege. */
 	  .policy = datapath_policy,
 	  .doit = ovs_dp_cmd_new
 	},
 	{ .cmd = OVS_DP_CMD_DEL,
-	  .flags = GENL_ADMIN_PERM, /* Requires CAP_NET_ADMIN privilege. */
+	  .flags = GENL_UNS_ADMIN_PERM, /* Requires CAP_NET_ADMIN privilege. */
 	  .policy = datapath_policy,
 	  .doit = ovs_dp_cmd_del
 	},
@@ -1793,7 +1793,7 @@ static const struct genl_ops dp_datapath_genl_ops[] = {
 	  .dumpit = ovs_dp_cmd_dump
 	},
 	{ .cmd = OVS_DP_CMD_SET,
-	  .flags = GENL_ADMIN_PERM, /* Requires CAP_NET_ADMIN privilege. */
+	  .flags = GENL_UNS_ADMIN_PERM, /* Requires CAP_NET_ADMIN privilege. */
 	  .policy = datapath_policy,
 	  .doit = ovs_dp_cmd_set,
 	},
@@ -2158,12 +2158,12 @@ static const struct nla_policy vport_policy[OVS_VPORT_ATTR_MAX + 1] = {
 
 static const struct genl_ops dp_vport_genl_ops[] = {
 	{ .cmd = OVS_VPORT_CMD_NEW,
-	  .flags = GENL_ADMIN_PERM, /* Requires CAP_NET_ADMIN privilege. */
+	  .flags = GENL_UNS_ADMIN_PERM, /* Requires CAP_NET_ADMIN privilege. */
 	  .policy = vport_policy,
 	  .doit = ovs_vport_cmd_new
 	},
 	{ .cmd = OVS_VPORT_CMD_DEL,
-	  .flags = GENL_ADMIN_PERM, /* Requires CAP_NET_ADMIN privilege. */
+	  .flags = GENL_UNS_ADMIN_PERM, /* Requires CAP_NET_ADMIN privilege. */
 	  .policy = vport_policy,
 	  .doit = ovs_vport_cmd_del
 	},
@@ -2174,7 +2174,7 @@ static const struct genl_ops dp_vport_genl_ops[] = {
 	  .dumpit = ovs_vport_cmd_dump
 	},
 	{ .cmd = OVS_VPORT_CMD_SET,
-	  .flags = GENL_ADMIN_PERM, /* Requires CAP_NET_ADMIN privilege. */
+	  .flags = GENL_UNS_ADMIN_PERM, /* Requires CAP_NET_ADMIN privilege. */
 	  .policy = vport_policy,
 	  .doit = ovs_vport_cmd_set,
 	},