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packet: nlmon: virtual netlink monitoring device for packet sockets
Currently, there is no good possibility to debug netlink traffic that is being exchanged between kernel and user space. Therefore, this patch implements a netlink virtual device, so that netlink messages will be made visible to PF_PACKET sockets. Once there was an approach with a similar idea [1], but it got forgotten somehow. I think it makes most sense to accept the "overhead" of an extra netlink net device over implementing the same functionality from PF_PACKET sockets once again into netlink sockets. We have BPF filters that can already be easily applied which even have netlink extensions, we have RX_RING zero-copy between kernel- and user space that can be reused, and much more features. So instead of re-implementing all of this, we simply pass the skb to a given PF_PACKET socket for further analysis. Another nice benefit that comes from that is that no code needs to be changed in user space packet analyzers (maybe adding a dissector, but not more), thus out of the box, we can already capture pcap files of netlink traffic to debug/troubleshoot netlink problems. Also thanks goes to Thomas Graf, Flavio Leitner, Jesper Dangaard Brouer. [1] http://marc.info/?l=linux-netdev&m=113813401516110 Signed-off-by: Daniel Borkmann <dborkman@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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3 changed files with 181 additions and 0 deletions
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@ -240,6 +240,16 @@ config VIRTIO_NET
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This is the virtual network driver for virtio. It can be used with
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lguest or QEMU based VMMs (like KVM or Xen). Say Y or M.
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config NLMON
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tristate "Virtual netlink monitoring device"
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---help---
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This option enables a monitoring net device for netlink skbs. The
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purpose of this is to analyze netlink messages with packet sockets.
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Thus applications like tcpdump will be able to see local netlink
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messages if they tap into the netlink device, record pcaps for further
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diagnostics, etc. This is mostly intended for developers or support
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to debug netlink issues. If unsure, say N.
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endif # NET_CORE
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config SUNGEM_PHY
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@ -22,6 +22,7 @@ obj-$(CONFIG_TUN) += tun.o
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obj-$(CONFIG_VETH) += veth.o
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obj-$(CONFIG_VIRTIO_NET) += virtio_net.o
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obj-$(CONFIG_VXLAN) += vxlan.o
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obj-$(CONFIG_NLMON) += nlmon.o
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#
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# Networking Drivers
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170
drivers/net/nlmon.c
Normal file
170
drivers/net/nlmon.c
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@ -0,0 +1,170 @@
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#include <linux/module.h>
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#include <linux/kernel.h>
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#include <linux/netdevice.h>
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#include <linux/netlink.h>
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#include <net/net_namespace.h>
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#include <linux/if_arp.h>
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struct pcpu_lstats {
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u64 packets;
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u64 bytes;
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struct u64_stats_sync syncp;
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};
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static netdev_tx_t nlmon_xmit(struct sk_buff *skb, struct net_device *dev)
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{
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int len = skb->len;
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struct pcpu_lstats *stats = this_cpu_ptr(dev->lstats);
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u64_stats_update_begin(&stats->syncp);
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stats->bytes += len;
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stats->packets++;
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u64_stats_update_end(&stats->syncp);
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dev_kfree_skb(skb);
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return NETDEV_TX_OK;
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}
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static int nlmon_is_valid_mtu(int new_mtu)
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{
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return new_mtu >= sizeof(struct nlmsghdr) && new_mtu <= INT_MAX;
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}
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static int nlmon_change_mtu(struct net_device *dev, int new_mtu)
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{
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if (!nlmon_is_valid_mtu(new_mtu))
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return -EINVAL;
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dev->mtu = new_mtu;
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return 0;
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}
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static int nlmon_dev_init(struct net_device *dev)
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{
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dev->lstats = alloc_percpu(struct pcpu_lstats);
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return dev->lstats == NULL ? -ENOMEM : 0;
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}
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static void nlmon_dev_uninit(struct net_device *dev)
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{
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free_percpu(dev->lstats);
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}
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static struct netlink_tap nlmon_tap;
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static int nlmon_open(struct net_device *dev)
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{
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return netlink_add_tap(&nlmon_tap);
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}
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static int nlmon_close(struct net_device *dev)
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{
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return netlink_remove_tap(&nlmon_tap);
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}
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static struct rtnl_link_stats64 *
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nlmon_get_stats64(struct net_device *dev, struct rtnl_link_stats64 *stats)
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{
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int i;
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u64 bytes = 0, packets = 0;
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for_each_possible_cpu(i) {
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const struct pcpu_lstats *nl_stats;
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u64 tbytes, tpackets;
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unsigned int start;
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nl_stats = per_cpu_ptr(dev->lstats, i);
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do {
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start = u64_stats_fetch_begin_bh(&nl_stats->syncp);
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tbytes = nl_stats->bytes;
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tpackets = nl_stats->packets;
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} while (u64_stats_fetch_retry_bh(&nl_stats->syncp, start));
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packets += tpackets;
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bytes += tbytes;
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}
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stats->rx_packets = packets;
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stats->tx_packets = 0;
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stats->rx_bytes = bytes;
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stats->tx_bytes = 0;
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return stats;
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}
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static u32 always_on(struct net_device *dev)
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{
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return 1;
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}
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static const struct ethtool_ops nlmon_ethtool_ops = {
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.get_link = always_on,
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};
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static const struct net_device_ops nlmon_ops = {
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.ndo_init = nlmon_dev_init,
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.ndo_uninit = nlmon_dev_uninit,
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.ndo_open = nlmon_open,
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.ndo_stop = nlmon_close,
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.ndo_start_xmit = nlmon_xmit,
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.ndo_get_stats64 = nlmon_get_stats64,
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.ndo_change_mtu = nlmon_change_mtu,
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};
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static struct netlink_tap nlmon_tap __read_mostly = {
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.module = THIS_MODULE,
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};
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static void nlmon_setup(struct net_device *dev)
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{
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dev->type = ARPHRD_NETLINK;
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dev->tx_queue_len = 0;
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dev->netdev_ops = &nlmon_ops;
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dev->ethtool_ops = &nlmon_ethtool_ops;
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dev->destructor = free_netdev;
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dev->features = NETIF_F_FRAGLIST | NETIF_F_HIGHDMA;
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dev->flags = IFF_NOARP;
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/* That's rather a softlimit here, which, of course,
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* can be altered. Not a real MTU, but what is to be
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* expected in most cases.
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*/
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dev->mtu = NLMSG_GOODSIZE;
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}
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static __init int nlmon_register(void)
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{
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int err;
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struct net_device *nldev;
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nldev = nlmon_tap.dev = alloc_netdev(0, "netlink", nlmon_setup);
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if (unlikely(nldev == NULL))
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return -ENOMEM;
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err = register_netdev(nldev);
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if (unlikely(err))
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free_netdev(nldev);
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return err;
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}
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static __exit void nlmon_unregister(void)
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{
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struct net_device *nldev = nlmon_tap.dev;
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unregister_netdev(nldev);
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}
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module_init(nlmon_register);
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module_exit(nlmon_unregister);
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MODULE_LICENSE("GPL v2");
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MODULE_AUTHOR("Daniel Borkmann <dborkman@redhat.com>");
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MODULE_AUTHOR("Mathieu Geli <geli@enseirb.fr>");
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MODULE_DESCRIPTION("Netlink monitoring device");
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