[PATCH RFC v2 net-next 00/25] rtnetlink: Add support for rigid checking of data in dump request

[David Ahern <dsahern@kernel.org>]

From: David Ahern <dsahern@gmail.com>

There are many use cases where a user wants to influence what is
returned in a dump for some rtnetlink command: one is wanting data
for a different namespace than the one the request is received and
another is limiting the amount of data returned in the dump to a
specific set of interest to userspace, reducing the cpu overhead of
both kernel and userspace. Unfortunately, the kernel has historically
not been strict with checking for the proper header or checking the
values passed in the header. This lenient implementation has allowed
iproute2 and other packages to pass any struct or data in the dump
request as long as the family is the first byte. For example, ifinfomsg
struct is used by iproute2 for all generic dump requests - links,
addresses, routes and rules when it is really only valid for link
requests.

There is 1 is example where the kernel deals with the wrong struct: link
dumps after VF support was added. Older iproute2 was sending rtgenmsg as
the header instead of ifinfomsg so a patch was added to try and detect
old userspace vs new:
e5eca6d41f53 ("rtnetlink: fix userspace API breakage for iproute2 < v3.9.0")

The latest example is Christian's patch set wanting to return addresses for
a target namespace. It guesses the header struct is an ifaddrmsg and if it
guesses wrong a netlink warning is generated in the kernel log on every
address dump which is unacceptable.

Another example where the kernel is a bit lenient is route dumps: iproute2
can send either a request with either ifinfomsg or a rtmsg as the header
struct, yet the kernel always treats the header as an rtmsg (see
inet_dump_fib and rtm_flags check). The header inconsistency impacts the
ability to add kernel side filters for route dumps - a necessary feature
for scale setups with 100k+ routes.

How to resolve the problem of not breaking old userspace yet be able to
move forward with new features such as kernel side filtering which are
crucial for efficient operation at high scale?

This patch set addresses the problem by adding a new netlink flag,
NLM_F_DUMP_PROPER_HDR, that userspace can set to say "I have a clue, and
I am sending the right header struct" and that the struct fields and any
attributes after it should be used for filtering the data returned in the
dump.

Kernel side, the dump handlers are updated to verify the message contains
at least the expected header struct:
    RTM_GETLINK:       ifinfomsg
    RTM_GETADDR:       ifaddrmsg
    RTM_GETMULTICAST:  ifaddrmsg
    RTM_GETANYCAST:    ifaddrmsg
    RTM_GETADDRLABEL:  ifaddrlblmsg
    RTM_GETROUTE:      rtmsg
    RTM_GETSTATS:      if_stats_msg
    RTM_GETNEIGH:      ndmsg
    RTM_GETNEIGHTBL:   ndtmsg
    RTM_GETNSID:       rtnl_net_dumpid
    RTM_GETRULE:       fib_rule_hdr
    RTM_GETNETCONF:    netconfmsg
    RTM_GETMDB:        br_port_msg

And then every field in the header struct should be 0 with the exception
of the family. There are a few exceptions to this rule where the kernel
already influences the data returned by values in the struct. Next the
message should not contain attributes unless the kernel implements
filtering for it. Any unexpected data causes the dump to fail with EINVAL.
If the new flag is honored by the kernel and the dump contents adjusted
by any data passed in the request, the dump handler can set the
NLM_F_DUMP_FILTERED flag in the netlink message header.

As an example of how this new NLM_F_DUMP_PROPER_HDR can be leveraged,
the last 6 patch add filtering of route dumps based on table id, protocol,
tos, flags, scope, and egress device.

David Ahern (25):
  net/netlink: Pass extack to dump callbacks
  net/ipv6: Refactor address dump to push inet6_fill_args to
    in6_dump_addrs
  netlink: introduce NLM_F_DUMP_PROPER_HDR flag
  net/ipv4: Update inet_dump_ifaddr to support NLM_F_DUMP_PROPER_HDR
  net/ipv6: Update inet6_dump_addr to support NLM_F_DUMP_PROPER_HDR
  rtnetlink: Update rtnl_dump_ifinfo to support NLM_F_DUMP_PROPER_HDR
  rtnetlink: Update rtnl_bridge_getlink to support NLM_F_DUMP_PROPER_HDR
  rtnetlink: Update rtnl_stats_dump to support NLM_F_DUMP_PROPER_HDR
  rtnetlink: Update inet6_dump_ifinfo to support NLM_F_DUMP_PROPER_HDR
  rtnetlink: Update ipmr_rtm_dumplink to support NLM_F_DUMP_PROPER_HDR
  rtnetlink: Update fib dumps to support NLM_F_DUMP_PROPER_HDR
  net/neigh: Refactor dump filter handling
  net/neighbor: Update neigh_dump_info to support NLM_F_DUMP_PROPER_HDR
  net/neighbor: Update neightbl_dump_info to support
    NLM_F_DUMP_PROPER_HDR
  net/namespace: Update rtnl_net_dumpid to support NLM_F_DUMP_PROPER_HDR
  net/fib_rules: Update fib_nl_dumprule to support NLM_F_DUMP_PROPER_HDR
  net/ipv6: Update ip6addrlbl_dump to support NLM_F_DUMP_PROPER_HDR
  net: Update netconf dump handlers to support NLM_F_DUMP_PROPER_HDR
  net/bridge: Update br_mdb_dump to support NLM_F_DUMP_PROPER_HDR
  net: Add struct for fib dump filter
  net/ipv4: Plumb support for filtering route dumps
  net/ipv6: Plumb support for filtering route dumps
  net/mpls: Plumb support for filtering route dumps
  net: Plumb support for filtering ipv4 and ipv6 multicast route dumps
  net: Enable kernel side filtering of route dumps

 include/linux/mroute_base.h  |   5 +-
 include/linux/netlink.h      |   2 +
 include/net/ip6_route.h      |   1 +
 include/net/ip_fib.h         |  16 +++-
 include/uapi/linux/netlink.h |   1 +
 net/bridge/br_mdb.c          |  20 ++++-
 net/core/fib_rules.c         |  25 +++++-
 net/core/neighbour.c         | 136 +++++++++++++++++++++++--------
 net/core/net_namespace.c     |   8 ++
 net/core/rtnetlink.c         | 185 +++++++++++++++++++++++++++++++++----------
 net/ipv4/devinet.c           |  74 +++++++++++++----
 net/ipv4/fib_frontend.c      |  76 +++++++++++++++++-
 net/ipv4/fib_trie.c          |  33 +++++---
 net/ipv4/ipmr.c              |  44 +++++++++-
 net/ipv4/ipmr_base.c         |  42 +++++++++-
 net/ipv6/addrconf.c          | 160 ++++++++++++++++++++++++++++---------
 net/ipv6/addrlabel.c         |  25 +++++-
 net/ipv6/ip6_fib.c           |  23 +++++-
 net/ipv6/ip6mr.c             |  12 ++-
 net/ipv6/route.c             |  36 ++++++---
 net/mpls/af_mpls.c           |  82 ++++++++++++++++++-
 net/netlink/af_netlink.c     |  20 +++--
 22 files changed, 860 insertions(+), 166 deletions(-)

-- 
2.11.0