vxlan: Support user-defined reserved bits

Currently the VXLAN header validation works by vxlan_rcv() going feature
by feature, each feature clearing the bits that it consumes. If anything
is left unparsed at the end, the packet is rejected.

Unfortunately there are machines out there that send VXLAN packets with
reserved bits set, even if they are configured to not use the
corresponding features. One such report is here[1], and we have heard
similar complaints from our customers as well.

This patchset adds an attribute that makes it configurable which bits
the user wishes to tolerate and which they consider reserved. This was
recommended in [1] as well.

A knob like that inevitably allows users to set as reserved bits that
are in fact required for the features enabled by the netdevice, such as
GPE. This is detected, and such configurations are rejected.

In patches #1..#7, the reserved bits validation code is gradually moved
away from the unparsed approach described above, to one where a given
set of valid bits is precomputed and then the packet is validated
against that.

In patch #8, this precomputed set is made configurable through a new
attribute IFLA_VXLAN_RESERVED_BITS.

Patches #9 and #10 massage the testsuite a bit, so that patch #11 can
introduce a selftest for the resreved bits feature.

The corresponding iproute2 support is available in [2].

[1] https://lore.kernel.org/netdev/db8b9e19-ad75-44d3-bfb2-46...
[2] https://github.com/pmachata/iproute2/commits/vxlan_reserv...

v2:
- Patch #11:
    - Add the new test to Makefile

v1 (vs. RFC):
- No changes.

Petr Machata (11):
  vxlan: In vxlan_rcv(), access flags through the vxlan netdevice
  vxlan: vxlan_rcv() callees: Move clearing of unparsed flags out
  vxlan: vxlan_rcv() callees: Drop the unparsed argument
  vxlan: vxlan_rcv(): Extract vxlan_hdr(skb) to a named variable
  vxlan: Track reserved bits explicitly as part of the configuration
  vxlan: Bump error counters for header mismatches
  vxlan: vxlan_rcv(): Drop unparsed
  vxlan: Add an attribute to make VXLAN header validation configurable
  selftests: net: lib: Rename ip_link_master() to ip_link_set_master()
  selftests: net: lib: Add several autodefer helpers
  selftests: forwarding: Add a selftest for the new reserved_bits UAPI

 drivers/net/vxlan/vxlan_core.c                | 150 +++++---
 include/net/vxlan.h                           |   1 +
 include/uapi/linux/if_link.h                  |   1 +
 tools/testing/selftests/net/fdb_notify.sh     |   6 +-
 .../testing/selftests/net/forwarding/Makefile |   1 +
 tools/testing/selftests/net/forwarding/lib.sh |   7 -
 .../net/forwarding/vxlan_reserved.sh          | 352 ++++++++++++++++++
 tools/testing/selftests/net/lib.sh            |  41 +-
 8 files changed, 497 insertions(+), 62 deletions(-)
 create mode 100755 tools/testing/selftests/net/forwarding/vxlan_reserved.sh

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2.47.0