From e4fc408e0e99fd2e009c8b3702d9637f5554fd5c Mon Sep 17 00:00:00 2001 From: Daniel Borkmann Date: Fri, 21 Jun 2013 19:38:08 +0200 Subject: [PATCH] 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 Signed-off-by: David S. Miller --- drivers/net/Kconfig | 10 +++ drivers/net/Makefile | 1 + drivers/net/nlmon.c | 170 +++++++++++++++++++++++++++++++++++++++++++ 3 files changed, 181 insertions(+) create mode 100644 drivers/net/nlmon.c diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig index 00aba08f01a9..b45b240889f5 100644 --- a/drivers/net/Kconfig +++ b/drivers/net/Kconfig @@ -240,6 +240,16 @@ config VIRTIO_NET This is the virtual network driver for virtio. It can be used with lguest or QEMU based VMMs (like KVM or Xen). Say Y or M. +config NLMON + tristate "Virtual netlink monitoring device" + ---help--- + This option enables a monitoring net device for netlink skbs. The + purpose of this is to analyze netlink messages with packet sockets. + Thus applications like tcpdump will be able to see local netlink + messages if they tap into the netlink device, record pcaps for further + diagnostics, etc. This is mostly intended for developers or support + to debug netlink issues. If unsure, say N. + endif # NET_CORE config SUNGEM_PHY diff --git a/drivers/net/Makefile b/drivers/net/Makefile index ef3d090efedf..3fef8a81c0f6 100644 --- a/drivers/net/Makefile +++ b/drivers/net/Makefile @@ -22,6 +22,7 @@ obj-$(CONFIG_TUN) += tun.o obj-$(CONFIG_VETH) += veth.o obj-$(CONFIG_VIRTIO_NET) += virtio_net.o obj-$(CONFIG_VXLAN) += vxlan.o +obj-$(CONFIG_NLMON) += nlmon.o # # Networking Drivers diff --git a/drivers/net/nlmon.c b/drivers/net/nlmon.c new file mode 100644 index 000000000000..dc364be6e61e --- /dev/null +++ b/drivers/net/nlmon.c @@ -0,0 +1,170 @@ +#include +#include +#include +#include +#include +#include + +struct pcpu_lstats { + u64 packets; + u64 bytes; + struct u64_stats_sync syncp; +}; + +static netdev_tx_t nlmon_xmit(struct sk_buff *skb, struct net_device *dev) +{ + int len = skb->len; + struct pcpu_lstats *stats = this_cpu_ptr(dev->lstats); + + u64_stats_update_begin(&stats->syncp); + stats->bytes += len; + stats->packets++; + u64_stats_update_end(&stats->syncp); + + dev_kfree_skb(skb); + + return NETDEV_TX_OK; +} + +static int nlmon_is_valid_mtu(int new_mtu) +{ + return new_mtu >= sizeof(struct nlmsghdr) && new_mtu <= INT_MAX; +} + +static int nlmon_change_mtu(struct net_device *dev, int new_mtu) +{ + if (!nlmon_is_valid_mtu(new_mtu)) + return -EINVAL; + + dev->mtu = new_mtu; + return 0; +} + +static int nlmon_dev_init(struct net_device *dev) +{ + dev->lstats = alloc_percpu(struct pcpu_lstats); + + return dev->lstats == NULL ? -ENOMEM : 0; +} + +static void nlmon_dev_uninit(struct net_device *dev) +{ + free_percpu(dev->lstats); +} + +static struct netlink_tap nlmon_tap; + +static int nlmon_open(struct net_device *dev) +{ + return netlink_add_tap(&nlmon_tap); +} + +static int nlmon_close(struct net_device *dev) +{ + return netlink_remove_tap(&nlmon_tap); +} + +static struct rtnl_link_stats64 * +nlmon_get_stats64(struct net_device *dev, struct rtnl_link_stats64 *stats) +{ + int i; + u64 bytes = 0, packets = 0; + + for_each_possible_cpu(i) { + const struct pcpu_lstats *nl_stats; + u64 tbytes, tpackets; + unsigned int start; + + nl_stats = per_cpu_ptr(dev->lstats, i); + + do { + start = u64_stats_fetch_begin_bh(&nl_stats->syncp); + tbytes = nl_stats->bytes; + tpackets = nl_stats->packets; + } while (u64_stats_fetch_retry_bh(&nl_stats->syncp, start)); + + packets += tpackets; + bytes += tbytes; + } + + stats->rx_packets = packets; + stats->tx_packets = 0; + + stats->rx_bytes = bytes; + stats->tx_bytes = 0; + + return stats; +} + +static u32 always_on(struct net_device *dev) +{ + return 1; +} + +static const struct ethtool_ops nlmon_ethtool_ops = { + .get_link = always_on, +}; + +static const struct net_device_ops nlmon_ops = { + .ndo_init = nlmon_dev_init, + .ndo_uninit = nlmon_dev_uninit, + .ndo_open = nlmon_open, + .ndo_stop = nlmon_close, + .ndo_start_xmit = nlmon_xmit, + .ndo_get_stats64 = nlmon_get_stats64, + .ndo_change_mtu = nlmon_change_mtu, +}; + +static struct netlink_tap nlmon_tap __read_mostly = { + .module = THIS_MODULE, +}; + +static void nlmon_setup(struct net_device *dev) +{ + dev->type = ARPHRD_NETLINK; + dev->tx_queue_len = 0; + + dev->netdev_ops = &nlmon_ops; + dev->ethtool_ops = &nlmon_ethtool_ops; + dev->destructor = free_netdev; + + dev->features = NETIF_F_FRAGLIST | NETIF_F_HIGHDMA; + dev->flags = IFF_NOARP; + + /* That's rather a softlimit here, which, of course, + * can be altered. Not a real MTU, but what is to be + * expected in most cases. + */ + dev->mtu = NLMSG_GOODSIZE; +} + +static __init int nlmon_register(void) +{ + int err; + struct net_device *nldev; + + nldev = nlmon_tap.dev = alloc_netdev(0, "netlink", nlmon_setup); + if (unlikely(nldev == NULL)) + return -ENOMEM; + + err = register_netdev(nldev); + if (unlikely(err)) + free_netdev(nldev); + + return err; +} + +static __exit void nlmon_unregister(void) +{ + struct net_device *nldev = nlmon_tap.dev; + + unregister_netdev(nldev); +} + +module_init(nlmon_register); +module_exit(nlmon_unregister); + +MODULE_LICENSE("GPL v2"); +MODULE_AUTHOR("Daniel Borkmann "); +MODULE_AUTHOR("Mathieu Geli "); +MODULE_DESCRIPTION("Netlink monitoring device"); -- 2.20.1