ipv6: ioam: Replace 0-length array with flexible array

Zero-length arrays are deprecated[1]. Replace struct ioam6_trace_hdr's
"data" 0-length array with a flexible array. Detected with GCC 13,
using -fstrict-flex-arrays=3:

net/ipv6/ioam6_iptunnel.c: In function 'ioam6_build_state':
net/ipv6/ioam6_iptunnel.c:194:37: warning: array subscript <unknown> is outside array bounds of '__u8[0]' {aka 'unsigned char[]'} [-Warray-bounds=]
194 | tuninfo->traceh.data[trace->remlen * 4] = IPV6_TLV_PADN;
| ~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~
In file included from include/linux/ioam6.h:11,
from net/ipv6/ioam6_iptunnel.c:13:
include/uapi/linux/ioam6.h:130:17: note: while referencing 'data'
130 | __u8 data[0];
| ^~~~

[1] https://www.kernel.org/doc/html/latest/process/deprecated.html#zero-length-and-one-element-arrays

Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Reviewed-by: Justin Iurman <justin.iurman@uliege.be>
Tested-by: Justin Iurman <justin.iurman@uliege.be>
Link: https://lore.kernel.org/r/20230105222115.never.661-kees@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

ipv6: ioam: Support for IOAM injection with lwtunnels

Add support for the IOAM inline insertion (only for the host-to-host use case)
which is per-route configured with lightweight tunnels. The target is iproute2
and the patch is ready. It will be posted as soon as this patchset is merged.
Here is an overview:

$ ip -6 ro ad fc00::1/128 encap ioam6 trace type 0x800000 ns 1 size 12 dev eth0

This example configures an IOAM Pre-allocated Trace option attached to the
fc00::1/128 prefix. The IOAM namespace (ns) is 1, the size of the pre-allocated
trace data block is 12 octets (size) and only the first IOAM data (bit 0:
hop_limit + node id) is included in the trace (type) represented as a bitfield.

The reason why the in-transit (IPv6-in-IPv6 encapsulation) use case is not
implemented is explained on the patchset cover.

Signed-off-by: Justin Iurman <justin.iurman@uliege.be>
Signed-off-by: David S. Miller <davem@davemloft.net>

ipv6: ioam: Data plane support for Pre-allocated Trace

Implement support for processing the IOAM Pre-allocated Trace with IPv6,
see [1] and [2]. Introduce a new IPv6 Hop-by-Hop TLV option, see IANA [3].

A new per-interface sysctl is introduced. The value is a boolean to accept (=1)
or ignore (=0, by default) IPv6 IOAM options on ingress for an interface:
- net.ipv6.conf.XXX.ioam6_enabled

Two other sysctls are introduced to define IOAM IDs, represented by an integer.
They are respectively per-namespace and per-interface:
- net.ipv6.ioam6_id
- net.ipv6.conf.XXX.ioam6_id

The value of the first one represents the IOAM ID of the node itself (u32; max
and default value = U32_MAX>>8, due to hop limit concatenation) while the other
represents the IOAM ID of an interface (u16; max and default value = U16_MAX).

Each "ioam6_id" sysctl has a "_wide" equivalent:
- net.ipv6.ioam6_id_wide
- net.ipv6.conf.XXX.ioam6_id_wide

The value of the first one represents the wide IOAM ID of the node itself (u64;
max and default value = U64_MAX>>8, due to hop limit concatenation) while the
other represents the wide IOAM ID of an interface (u32; max and default value
= U32_MAX).

The use of short and wide equivalents is not exclusive, a deployment could
choose to leverage both. For example, net.ipv6.conf.XXX.ioam6_id (short format)
could be an identifier for a physical interface, whereas
net.ipv6.conf.XXX.ioam6_id_wide (wide format) could be an identifier for a
logical sub-interface. Documentation about new sysctls is provided at the end
of this patchset.

Two relativistic hash tables are used: one for IOAM namespaces, the other for
IOAM schemas. A namespace can only have a single active schema and a schema
can only be attached to a single namespace (1:1 relationship).

[1] https://tools.ietf.org/html/draft-ietf-ippm-ioam-ipv6-options
[2] https://tools.ietf.org/html/draft-ietf-ippm-ioam-data
[3] https://www.iana.org/assignments/ipv6-parameters/ipv6-parameters.xhtml#ipv6-parameters-2

Signed-off-by: Justin Iurman <justin.iurman@uliege.be>
Signed-off-by: David S. Miller <davem@davemloft.net>

uapi: IPv6 IOAM headers definition

This patch provides the IPv6 IOAM option header [1] as well as the IOAM
Trace header [2]. An IOAM option must be 4n-aligned. Here is an overview of
a Hop-by-Hop with an IOAM Trace option:

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next header | Hdr Ext Len | Padding | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type | Opt Data Len | Reserved | IOAM Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Namespace-ID | NodeLen | Flags | RemainingLen|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IOAM-Trace-Type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<-+
| | |
| node data [n] | |
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ D
| | a
| node data [n-1] | t
| | a
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ... ~ S
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ p
| | a
| node data [1] | c
| | e
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | |
| node data [0] | |
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<-+

The IOAM option header starts at "Option Type" and ends after "IOAM
Type". The IOAM Trace header starts at "Namespace-ID" and ends after
"IOAM-Trace-Type/Reserved".

IOAM Type: either Pre-allocated Trace (=0), Incremental Trace (=1),
Proof-of-Transit (=2) or Edge-to-Edge (=3). Note that both the
Pre-allocated Trace and the Incremental Trace look the same. The two
others are not implemented.

Namespace-ID: IOAM namespace identifier, not to be confused with network
namespaces. It adds further context to IOAM options and associated data,
and allows devices which are IOAM capable to determine whether IOAM
options must be processed or ignored. It can also be used by an operator
to distinguish different operational domains or to identify different
sets of devices.

NodeLen: Length of data added by each node. It depends on the Trace
Type.

Flags: Only the Overflow (O) flag for now. The O flag is set by a
transit node when there are not enough octets left to record its data.

RemainingLen: Remaining free space to record data.

IOAM-Trace-Type: Bit field where each bit corresponds to a specific kind
of IOAM data. See [2] for a detailed list.

[1] https://tools.ietf.org/html/draft-ietf-ippm-ioam-ipv6-options
[2] https://tools.ietf.org/html/draft-ietf-ippm-ioam-data

Signed-off-by: Justin Iurman <justin.iurman@uliege.be>
Signed-off-by: David S. Miller <davem@davemloft.net>