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>
diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
index 00aba08..b45b240 100644
--- a/drivers/net/Kconfig
+++ b/drivers/net/Kconfig
@@ -240,6 +240,16 @@
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