Commit 7458575a authored by Andrea Mayer's avatar Andrea Mayer Committed by Jakub Kicinski
Browse files

seg6: add NEXT-C-SID support for SRv6 End.X behavior 

The NEXT-C-SID mechanism described in [1] offers the possibility of
encoding several SRv6 segments within a single 128 bit SID address. Such
a SID address is called a Compressed SID (C-SID) container. In this way,
the length of the SID List can be drastically reduced.

A SID instantiated with the NEXT-C-SID flavor considers an IPv6 address
logically structured in three main blocks: i) Locator-Block; ii)
Locator-Node Function; iii) Argument.

                        C-SID container
+------------------------------------------------------------------+
|     Locator-Block      |Loc-Node|            Argument            |
|                        |Function|                                |
+------------------------------------------------------------------+
<--------- B -----------> <- NF -> <------------- A --------------->

   (i) The Locator-Block can be any IPv6 prefix available to the provider;

  (ii) The Locator-Node Function represents the node and the function to
       be triggered when a packet is received on the node;

 (iii) The Argument carries the remaining C-SIDs in the current C-SID
       container.

This patch leverages the NEXT-C-SID mechanism previously introduced in the
Linux SRv6 subsystem [2] to support SID compression capabilities in the
SRv6 End.X behavior [3].
An SRv6 End.X behavior with NEXT-C-SID flavor works as an End.X behavior
but it is capable of processing the compressed SID List encoded in C-SID
containers.

An SRv6 End.X behavior with NEXT-C-SID flavor can be configured to support
user-provided Locator-Block and Locator-Node Function lengths. In this
implementation, such lengths must be evenly divisible by 8 (i.e. must be
byte-aligned), otherwise the kernel informs the user about invalid
values with a meaningful error code and message through netlink_ext_ack.

If Locator-Block and/or Locator-Node Function lengths are not provided
by the user during configuration of an SRv6 End.X behavior instance with
NEXT-C-SID flavor, the kernel will choose their default values i.e.,
32-bit Locator-Block and 16-bit Locator-Node Function.

[1] - https://datatracker.ietf.org/doc/html/draft-ietf-spring-srv6-srh-compression
[2] - https://lore.kernel.org/all/20220912171619.16943-1-andrea.mayer@uniroma2.it/
[3] - https://datatracker.ietf.org/doc/html/rfc8986#name-endx-l3-cross-connect



Signed-off-by: default avatarAndrea Mayer <andrea.mayer@uniroma2.it>
Reviewed-by: default avatarHangbin Liu <liuhangbin@gmail.com>
Reviewed-by: default avatarDavid Ahern <dsahern@kernel.org>
Link: https://lore.kernel.org/r/20230812180926.16689-2-andrea.mayer@uniroma2.it


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent c65dffc6

net/ipv6/seg6_local.c

+88 −20
Original line number Diff line number Diff line
@@ -109,15 +109,19 @@ struct bpf_lwt_prog { 
#define next_csid_chk_lcnode_fn_bits(flen)		\

	next_csid_chk_lcblock_bits(flen)



/* flag indicating that flavors are set up for a given End* behavior */

#define SEG6_F_LOCAL_FLAVORS		SEG6_F_ATTR(SEG6_LOCAL_FLAVORS)



#define SEG6_F_LOCAL_FLV_OP(flvname)	BIT(SEG6_LOCAL_FLV_OP_##flvname)

#define SEG6_F_LOCAL_FLV_NEXT_CSID	SEG6_F_LOCAL_FLV_OP(NEXT_CSID)

#define SEG6_F_LOCAL_FLV_PSP		SEG6_F_LOCAL_FLV_OP(PSP)



/* Supported RFC8986 Flavor operations are reported in this bitmask */

#define SEG6_LOCAL_FLV8986_SUPP_OPS	SEG6_F_LOCAL_FLV_PSP



/* Supported Flavor operations are reported in this bitmask */

#define SEG6_LOCAL_FLV_SUPP_OPS		(SEG6_F_LOCAL_FLV_OP(NEXT_CSID) | \

#define SEG6_LOCAL_END_FLV_SUPP_OPS	(SEG6_F_LOCAL_FLV_NEXT_CSID | \

					 SEG6_LOCAL_FLV8986_SUPP_OPS)

#define SEG6_LOCAL_END_X_FLV_SUPP_OPS	SEG6_F_LOCAL_FLV_NEXT_CSID



struct seg6_flavors_info {

	/* Flavor operations */
@@ -411,9 +415,72 @@ static int end_next_csid_core(struct sk_buff *skb, struct seg6_local_lwt *slwt) 
	return input_action_end_finish(skb, slwt);

}



static int input_action_end_x_finish(struct sk_buff *skb,

				     struct seg6_local_lwt *slwt)

{

	seg6_lookup_nexthop(skb, &slwt->nh6, 0);



	return dst_input(skb);

}



static int input_action_end_x_core(struct sk_buff *skb,

				   struct seg6_local_lwt *slwt)

{

	struct ipv6_sr_hdr *srh;



	srh = get_and_validate_srh(skb);

	if (!srh)

		goto drop;



	advance_nextseg(srh, &ipv6_hdr(skb)->daddr);



	return input_action_end_x_finish(skb, slwt);



drop:

	kfree_skb(skb);

	return -EINVAL;

}



static int end_x_next_csid_core(struct sk_buff *skb,

				struct seg6_local_lwt *slwt)

{

	const struct seg6_flavors_info *finfo = &slwt->flv_info;

	struct in6_addr *daddr = &ipv6_hdr(skb)->daddr;



	if (seg6_next_csid_is_arg_zero(daddr, finfo))

		return input_action_end_x_core(skb, slwt);



	/* update DA */

	seg6_next_csid_advance_arg(daddr, finfo);



	return input_action_end_x_finish(skb, slwt);

}



static bool seg6_next_csid_enabled(__u32 fops)

{

	return fops & BIT(SEG6_LOCAL_FLV_OP_NEXT_CSID);

	return fops & SEG6_F_LOCAL_FLV_NEXT_CSID;

}



/* Processing of SRv6 End, End.X, and End.T behaviors can be extended through

 * the flavors framework. These behaviors must report the subset of (flavor)

 * operations they currently implement. In this way, if a user specifies a

 * flavor combination that is not supported by a given End* behavior, the

 * kernel refuses to instantiate the tunnel reporting the error.

 */

static int seg6_flv_supp_ops_by_action(int action, __u32 *fops)

{

	switch (action) {

	case SEG6_LOCAL_ACTION_END:

		*fops = SEG6_LOCAL_END_FLV_SUPP_OPS;

		break;

	case SEG6_LOCAL_ACTION_END_X:

		*fops = SEG6_LOCAL_END_X_FLV_SUPP_OPS;

		break;

	default:

		return -EOPNOTSUPP;

	}



	return 0;

}



/* We describe the packet state in relation to the absence/presence of the SRH
@@ -746,21 +813,14 @@ static int input_action_end(struct sk_buff *skb, struct seg6_local_lwt *slwt) 
/* regular endpoint, and forward to specified nexthop */

static int input_action_end_x(struct sk_buff *skb, struct seg6_local_lwt *slwt)

{

	struct ipv6_sr_hdr *srh;



	srh = get_and_validate_srh(skb);

	if (!srh)

		goto drop;



	advance_nextseg(srh, &ipv6_hdr(skb)->daddr);



	seg6_lookup_nexthop(skb, &slwt->nh6, 0);

	const struct seg6_flavors_info *finfo = &slwt->flv_info;

	__u32 fops = finfo->flv_ops;



	return dst_input(skb);

	/* check for the presence of NEXT-C-SID since it applies first */

	if (seg6_next_csid_enabled(fops))

		return end_x_next_csid_core(skb, slwt);



drop:

	kfree_skb(skb);

	return -EINVAL;

	return input_action_end_x_core(skb, slwt);

}



static int input_action_end_t(struct sk_buff *skb, struct seg6_local_lwt *slwt)
@@ -1404,13 +1464,14 @@ static struct seg6_action_desc seg6_action_table[] = { 
		.action		= SEG6_LOCAL_ACTION_END,

		.attrs		= 0,

		.optattrs	= SEG6_F_LOCAL_COUNTERS |

				  SEG6_F_ATTR(SEG6_LOCAL_FLAVORS),

				  SEG6_F_LOCAL_FLAVORS,

		.input		= input_action_end,

	},

	{

		.action		= SEG6_LOCAL_ACTION_END_X,

		.attrs		= SEG6_F_ATTR(SEG6_LOCAL_NH6),

		.optattrs	= SEG6_F_LOCAL_COUNTERS,

		.optattrs	= SEG6_F_LOCAL_COUNTERS |

				  SEG6_F_LOCAL_FLAVORS,

		.input		= input_action_end_x,

	},

	{
@@ -2070,7 +2131,8 @@ static int parse_nla_flavors(struct nlattr **attrs, struct seg6_local_lwt *slwt, 
{

	struct seg6_flavors_info *finfo = &slwt->flv_info;

	struct nlattr *tb[SEG6_LOCAL_FLV_MAX + 1];

	unsigned long fops;

	int action = slwt->action;

	__u32 fops, supp_fops;

	int rc;



	rc = nla_parse_nested_deprecated(tb, SEG6_LOCAL_FLV_MAX,
@@ -2086,7 +2148,8 @@ static int parse_nla_flavors(struct nlattr **attrs, struct seg6_local_lwt *slwt, 
		return -EINVAL;



	fops = nla_get_u32(tb[SEG6_LOCAL_FLV_OPERATION]);

	if (fops & ~SEG6_LOCAL_FLV_SUPP_OPS) {

	rc = seg6_flv_supp_ops_by_action(action, &supp_fops);

	if (rc < 0 || (fops & ~supp_fops)) {

		NL_SET_ERR_MSG(extack, "Unsupported Flavor operation(s)");

		return -EOPNOTSUPP;

	}
@@ -2618,6 +2681,11 @@ int __init seg6_local_init(void) 
	 */

	BUILD_BUG_ON(SEG6_LOCAL_MAX + 1 > BITS_PER_TYPE(unsigned long));



	/* Check whether the number of defined flavors exceeds the maximum

	 * allowed value.

	 */

	BUILD_BUG_ON(SEG6_LOCAL_FLV_OP_MAX + 1 > BITS_PER_TYPE(__u32));



	/* If the default NEXT-C-SID Locator-Block/Node Function lengths (in

	 * bits) have been changed with invalid values, kernel build stops

	 * here.