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: Andrea Mayer <andrea.mayer@uniroma2.it>
Reviewed-by: Hangbin Liu <liuhangbin@gmail.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://lore.kernel.org/r/20230812180926.16689-2-andrea.mayer@uniroma2.it
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/ipv6/seg6_local.c b/net/ipv6/seg6_local.c
index dd433cc..24e2b4b 100644 (file)
--- a/net/ipv6/seg6_local.c
+++ b/net/ipv6/seg6_local.c
@@ -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.