Quoting Tycho Andersen (tycho.andersen@xxxxxxxxxxxxx):
> 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
>
> Reported-by: James Page <james.page@xxxxxxxxxxxxx>
> Signed-off-by: Tycho Andersen <tycho.andersen@xxxxxxxxxxxxx>
> CC: Eric Biederman <ebiederm@xxxxxxxxxxxx>
> CC: Pravin Shelar <pshelar@xxxxxxx>
> CC: Justin Pettit <jpettit@xxxxxxxxxx>
> CC: "David S. Miller" <davem@xxxxxxxxxxxxx>
> ---
> include/uapi/linux/genetlink.h | 1 +
> net/netlink/genetlink.c | 6 ++++--
> net/openvswitch/datapath.c | 20 ++++++++++----------
> 3 files changed, 15 insertions(+), 12 deletions(-)
>
> diff --git a/include/uapi/linux/genetlink.h b/include/uapi/linux/genetlink.h
> index c3363ba..5512c90 100644
> --- a/include/uapi/linux/genetlink.h
> +++ b/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:
> diff --git a/net/netlink/genetlink.c b/net/netlink/genetlink.c
> index f830326..6bbb3eb 100644
> --- a/net/netlink/genetlink.c
> +++ b/net/netlink/genetlink.c
> @@ -576,8 +576,10 @@ static int genl_family_rcv_msg(struct genl_family *family,
> if (ops == NULL)
> return -EOPNOTSUPP;
>
> - if ((ops->flags & GENL_ADMIN_PERM) &&
> - !netlink_capable(skb, CAP_NET_ADMIN))
> + if (((ops->flags & GENL_ADMIN_PERM) &&
> + !netlink_capable(skb, CAP_NET_ADMIN)) ||
Seems like this would be a lot clearer if you split it up, i.e.:
/* CAP_NET_ADMIN required against initial user_ns */
if ((ops->flags & GENL_ADMIN_PERM) &&
!netlink_capable(skb, CAP_NET_ADMIN))
return -EPERM;
/* CAP_NET_ADMIN required against device user_ns */
if ((ops->flags & GENL_UNS_ADMIN_PERM) &&
!netlink_ns_capable(skb, net->user_ns, CAP_NET_ADMIN))
return -EPERM;
> + ((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) {
> diff --git a/net/openvswitch/datapath.c b/net/openvswitch/datapath.c
> index deadfda..d6f7fe9 100644
> --- a/net/openvswitch/datapath.c
> +++ b/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. */
Hm, I'd like to suggest adding 'over netns', but I guess that breaks 80 cols...
> .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,
> },
> --
> 2.5.0
>
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