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 do permissions checks in each function, but use the netlink
socket's user ns instead of the initial one, to allow management of
openvswitch resources from inside a user ns.

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.

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>
---
 net/openvswitch/datapath.c | 63 ++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 53 insertions(+), 10 deletions(-)

Tycho Andersen <tycho.andersen@canonical.com> writes:

> 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 do permissions checks in each function, but use the netlink
> socket's user ns instead of the initial one, to allow management of
> openvswitch resources from inside a user ns.
>
> 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.

So at a quick look using ns_capable this way is probably buggy.

netlink is goofy (because historically we got this wrong), and I forget
what the specific rules are.  The general rule is that you need to do
your permission checks on open/create/connect and not inside send/write
while processing data.  Otherwise there is a class of privileged
applications where you can set their stdout to some precreated file
descriptor and their output can be made to act as a command, bypassing
your permission checks.

Eric

> 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>
> ---
>  net/openvswitch/datapath.c | 63 ++++++++++++++++++++++++++++++++++++++--------
>  1 file changed, 53 insertions(+), 10 deletions(-)
>
> diff --git a/net/openvswitch/datapath.c b/net/openvswitch/datapath.c
> index deadfda..aacfb11 100644
> --- a/net/openvswitch/datapath.c
> +++ b/net/openvswitch/datapath.c
> @@ -557,6 +557,10 @@ static int ovs_packet_cmd_execute(struct sk_buff *skb, struct genl_info *info)
>  	int err;
>  	bool log = !a[OVS_PACKET_ATTR_PROBE];
>  
> +	err = -EPERM;
> +	if (!ns_capable(net->user_ns, CAP_NET_ADMIN))
> +		goto err;
> +
>  	err = -EINVAL;
>  	if (!a[OVS_PACKET_ATTR_PACKET] || !a[OVS_PACKET_ATTR_KEY] ||
>  	    !a[OVS_PACKET_ATTR_ACTIONS])
> @@ -654,7 +658,7 @@ 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 = 0,
>  	  .policy = packet_policy,
>  	  .doit = ovs_packet_cmd_execute
>  	}
> @@ -920,6 +924,10 @@ static int ovs_flow_cmd_new(struct sk_buff *skb, struct genl_info *info)
>  	int error;
>  	bool log = !a[OVS_FLOW_ATTR_PROBE];
>  
> +	error = -EPERM;
> +	if (!ns_capable(net->user_ns, CAP_NET_ADMIN))
> +		goto error;
> +
>  	/* Must have key and actions. */
>  	error = -EINVAL;
>  	if (!a[OVS_FLOW_ATTR_KEY]) {
> @@ -1104,6 +1112,10 @@ static int ovs_flow_cmd_set(struct sk_buff *skb, struct genl_info *info)
>  	bool log = !a[OVS_FLOW_ATTR_PROBE];
>  	bool ufid_present;
>  
> +	error = -EPERM;
> +	if (!ns_capable(net->user_ns, CAP_NET_ADMIN))
> +		goto error;
> +
>  	/* Extract key. */
>  	error = -EINVAL;
>  	if (!a[OVS_FLOW_ATTR_KEY]) {
> @@ -1274,6 +1286,9 @@ static int ovs_flow_cmd_del(struct sk_buff *skb, struct genl_info *info)
>  	bool log = !a[OVS_FLOW_ATTR_PROBE];
>  	bool ufid_present;
>  
> +	if (!ns_capable(net->user_ns, CAP_NET_ADMIN))
> +		return -EPERM;
> +
>  	ufid_present = ovs_nla_get_ufid(&ufid, a[OVS_FLOW_ATTR_UFID], log);
>  	if (a[OVS_FLOW_ATTR_KEY]) {
>  		ovs_match_init(&match, &key, NULL);
> @@ -1391,12 +1406,12 @@ 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 = 0,
>  	  .policy = flow_policy,
>  	  .doit = ovs_flow_cmd_new
>  	},
>  	{ .cmd = OVS_FLOW_CMD_DEL,
> -	  .flags = GENL_ADMIN_PERM, /* Requires CAP_NET_ADMIN privilege. */
> +	  .flags = 0,
>  	  .policy = flow_policy,
>  	  .doit = ovs_flow_cmd_del
>  	},
> @@ -1407,7 +1422,7 @@ 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 = 0,
>  	  .policy = flow_policy,
>  	  .doit = ovs_flow_cmd_set,
>  	},
> @@ -1530,8 +1545,12 @@ static int ovs_dp_cmd_new(struct sk_buff *skb, struct genl_info *info)
>  	struct datapath *dp;
>  	struct vport *vport;
>  	struct ovs_net *ovs_net;
> +	struct net *net = sock_net(skb->sk);
>  	int err, i;
>  
> +	if (!ns_capable(net->user_ns, CAP_NET_ADMIN))
> +		return -EPERM;
> +
>  	err = -EINVAL;
>  	if (!a[OVS_DP_ATTR_NAME] || !a[OVS_DP_ATTR_UPCALL_PID])
>  		goto err;
> @@ -1655,8 +1674,12 @@ static int ovs_dp_cmd_del(struct sk_buff *skb, struct genl_info *info)
>  {
>  	struct sk_buff *reply;
>  	struct datapath *dp;
> +	struct net *net = sock_net(skb->sk);
>  	int err;
>  
> +	if (!ns_capable(net->user_ns, CAP_NET_ADMIN))
> +		return -EPERM;
> +
>  	reply = ovs_dp_cmd_alloc_info(info);
>  	if (!reply)
>  		return -ENOMEM;
> @@ -1688,8 +1711,12 @@ static int ovs_dp_cmd_set(struct sk_buff *skb, struct genl_info *info)
>  {
>  	struct sk_buff *reply;
>  	struct datapath *dp;
> +	struct net *net = sock_net(skb->sk);
>  	int err;
>  
> +	if (!ns_capable(net->user_ns, CAP_NET_ADMIN))
> +		return -EPERM;
> +
>  	reply = ovs_dp_cmd_alloc_info(info);
>  	if (!reply)
>  		return -ENOMEM;
> @@ -1721,8 +1748,12 @@ static int ovs_dp_cmd_get(struct sk_buff *skb, struct genl_info *info)
>  {
>  	struct sk_buff *reply;
>  	struct datapath *dp;
> +	struct net *net = sock_net(skb->sk);
>  	int err;
>  
> +	if (!ns_capable(net->user_ns, CAP_NET_ADMIN))
> +		return -EPERM;
> +
>  	reply = ovs_dp_cmd_alloc_info(info);
>  	if (!reply)
>  		return -ENOMEM;
> @@ -1777,12 +1808,12 @@ 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 = 0,
>  	  .policy = datapath_policy,
>  	  .doit = ovs_dp_cmd_new
>  	},
>  	{ .cmd = OVS_DP_CMD_DEL,
> -	  .flags = GENL_ADMIN_PERM, /* Requires CAP_NET_ADMIN privilege. */
> +	  .flags = 0,
>  	  .policy = datapath_policy,
>  	  .doit = ovs_dp_cmd_del
>  	},
> @@ -1793,7 +1824,7 @@ 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 = 0,
>  	  .policy = datapath_policy,
>  	  .doit = ovs_dp_cmd_set,
>  	},
> @@ -1920,9 +1951,13 @@ static int ovs_vport_cmd_new(struct sk_buff *skb, struct genl_info *info)
>  	struct sk_buff *reply;
>  	struct vport *vport;
>  	struct datapath *dp;
> +	struct net *net = sock_net(skb->sk);
>  	u32 port_no;
>  	int err;
>  
> +	if (!ns_capable(net->user_ns, CAP_NET_ADMIN))
> +		return -EPERM;
> +
>  	if (!a[OVS_VPORT_ATTR_NAME] || !a[OVS_VPORT_ATTR_TYPE] ||
>  	    !a[OVS_VPORT_ATTR_UPCALL_PID])
>  		return -EINVAL;
> @@ -1994,8 +2029,12 @@ static int ovs_vport_cmd_set(struct sk_buff *skb, struct genl_info *info)
>  	struct nlattr **a = info->attrs;
>  	struct sk_buff *reply;
>  	struct vport *vport;
> +	struct net *net = sock_net(skb->sk);
>  	int err;
>  
> +	if (!ns_capable(net->user_ns, CAP_NET_ADMIN))
> +		return -EPERM;
> +
>  	reply = ovs_vport_cmd_alloc_info();
>  	if (!reply)
>  		return -ENOMEM;
> @@ -2046,8 +2085,12 @@ static int ovs_vport_cmd_del(struct sk_buff *skb, struct genl_info *info)
>  	struct nlattr **a = info->attrs;
>  	struct sk_buff *reply;
>  	struct vport *vport;
> +	struct net *net = sock_net(skb->sk);
>  	int err;
>  
> +	if (!ns_capable(net->user_ns, CAP_NET_ADMIN))
> +		return -EPERM;
> +
>  	reply = ovs_vport_cmd_alloc_info();
>  	if (!reply)
>  		return -ENOMEM;
> @@ -2158,12 +2201,12 @@ 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 = 0,
>  	  .policy = vport_policy,
>  	  .doit = ovs_vport_cmd_new
>  	},
>  	{ .cmd = OVS_VPORT_CMD_DEL,
> -	  .flags = GENL_ADMIN_PERM, /* Requires CAP_NET_ADMIN privilege. */
> +	  .flags = 0,
>  	  .policy = vport_policy,
>  	  .doit = ovs_vport_cmd_del
>  	},
> @@ -2174,7 +2217,7 @@ 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 = 0,
>  	  .policy = vport_policy,
>  	  .doit = ovs_vport_cmd_set,
>  	},