[PATCH net-next 0/13] sk_buff: add extension infrastructure

[Florian Westphal <fw@strlen.de>]

The (out-of-tree) Multipath-TCP implementation needs to map logical mptcp
sequence numbers to the tcp sequence numbers used by individual subflows.
This DSS mapping is read/written from tcp option space on receive and
written to tcp option space on transmitted tcp packets that are part of
and MPTCP connection.

Increasing skb->cb[] size in mainline to store the DSS mapping
is a non-starter for memory and and performance reasons
(f.e. increase in cb size also moves several frequently-accessed fields
 to other cache lines).

Extend skb_shared_info or adding a private data field to skb fclones
doesn't work for incoming skb, so a different DSS propagation method
would be required for the receive side.

The current MPTCP implementation adds an additional mptcp specific
pointer to sk_buff.

This series adds an extension infrastructure for sk_buff instead:
1. extension memory is released when the sk_buff is free'd.
2. data is shared after cloning an skb.
3. adding extension to an skb will COW the extension buffer if needed.

This is also how xfrm and bridge_nf extra data (skb->sp, skb->nf_bridge)
are handled.

MPTCP could then add a new SKB_EXT_MPTCP_DSS (or similar) to store the
mapping for tx and rx processing.

Two new members are added to sk_buff:
1. 'active_extensions' byte (filling a hole), telling which extensions
   are available for this skb.
2. extension pointer, located at the end of the sk_buff.
   If the active_extensions byte is 0, the pointer is undefined.

Third patch converts nf_bridge to use the extension infrastructure:
The 'nf_bridge' pointer is removed, i.e. sk_buff size remains the same.

After this, there are a few preparation patches to reduce "skb->sp"
usage by using the secpath helper functions instead.

Last patch converts skb->sp, secpath information gets stored as
new SKB_EXT_SEC_PATH, so the 'sp' pointer is removed from skbuff.

Extra code added to skb clone and free paths (to deal with refcount/free
of extension area) replace the existing code that does the same for
skb->nf_bridge and skb->secpath.

I don't see any other in-tree users that could benefit from this
infrastructure, it doesn't make sense to add an extension just for the sake
of a single flag bit (like skb->nf_trace).

Changes since RFC:

Convert secpath.

Unlike nf_bridge, the secpath struct needs to hold reference on the
xfrm state structure(s), thus handling gets more complicated when
an existing secpath extension has to be COW'd (we need to take additional
reference count on the xfrm states contained in the new copy).

Florian Westphal (13):
      netfilter: avoid using skb->nf_bridge directly
      sk_buff: add skb extension infrastructure
      net: convert bridge_nf to use skb extension infrastructure
      xfrm: change secpath_set to return secpath struct, not error value
      net: move secpath_exist helper to sk_buff.h
      net: use skb_sec_path helper in more places
      drivers: net: intel: use secpath helpers in more places
      drivers: net: ethernet: mellanox: use skb_sec_path helper
      drivers: net: netdevsim: use skb_sec_path helper
      xfrm: use secpath_exist where applicable
      drivers: chelsio: use skb_sec_path helper
      xfrm: prefer secpath_set over secpath_dup
      net: switch secpath to use skb extension infrastructure

 Documentation/networking/xfrm_device.txt                      |    7 
 drivers/crypto/chelsio/chcr_ipsec.c                           |    4 
 drivers/net/ethernet/intel/ixgbe/ixgbe_ipsec.c                |   15 
 drivers/net/ethernet/intel/ixgbe/ixgbe_main.c                 |    5 
 drivers/net/ethernet/intel/ixgbevf/ipsec.c                    |   15 
 drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c             |    2 
 drivers/net/ethernet/mellanox/mlx5/core/en_accel/ipsec_rxtx.c |   19 -
 drivers/net/netdevsim/ipsec.c                                 |    7 
 include/linux/netfilter_bridge.h                              |   33 +
 include/linux/skbuff.h                                        |  160 +++++++-
 include/net/netfilter/br_netfilter.h                          |   14 
 include/net/xfrm.h                                            |   40 --
 net/Kconfig                                                   |    4 
 net/bridge/br_netfilter_hooks.c                               |   39 --
 net/bridge/br_netfilter_ipv6.c                                |    4 
 net/core/skbuff.c                                             |  182 +++++++++-
 net/ipv4/esp4.c                                               |    9 
 net/ipv4/esp4_offload.c                                       |   15 
 net/ipv4/ip_output.c                                          |    1 
 net/ipv4/netfilter/nf_reject_ipv4.c                           |    6 
 net/ipv6/esp6.c                                               |    9 
 net/ipv6/esp6_offload.c                                       |   15 
 net/ipv6/ip6_output.c                                         |    1 
 net/ipv6/netfilter/nf_reject_ipv6.c                           |   10 
 net/ipv6/xfrm6_input.c                                        |    8 
 net/netfilter/nf_log_common.c                                 |   20 -
 net/netfilter/nf_queue.c                                      |   50 +-
 net/netfilter/nfnetlink_queue.c                               |   23 -
 net/netfilter/nft_meta.c                                      |    2 
 net/netfilter/nft_xfrm.c                                      |    2 
 net/netfilter/xt_physdev.c                                    |    2 
 net/netfilter/xt_policy.c                                     |    2 
 net/xfrm/Kconfig                                              |    1 
 net/xfrm/xfrm_device.c                                        |    4 
 net/xfrm/xfrm_input.c                                         |   76 +---
 net/xfrm/xfrm_interface.c                                     |    2 
 net/xfrm/xfrm_output.c                                        |    7 
 net/xfrm/xfrm_policy.c                                        |   19 -
 security/selinux/xfrm.c                                       |    4 
 39 files changed, 553 insertions(+), 285 deletions(-)