ip_tunnels, bpf: define IP_TUNNEL_OPTS_MAX and use it

eBPF defines this as BPF_TUNLEN_MAX and OVS just uses the hard-coded
value inside struct sw_flow_key. Thus, add and use IP_TUNNEL_OPTS_MAX
for this, which makes the code a bit more generic and allows to remove
BPF_TUNLEN_MAX from eBPF code.

Signed-off-by: Daniel Borkmann <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/net/ip_tunnels.h

···
 #include <linux/socket.h>
 #include <linux/types.h>
 #include <linux/u64_stats_sync.h>
+#include <linux/bitops.h>
+
 #include <net/dsfield.h>
 #include <net/gro_cells.h>
 #include <net/inet_ecn.h>
···
 /* Flags for ip_tunnel_info mode. */
 #define IP_TUNNEL_INFO_TX	0x01	/* represents tx tunnel parameters */
 #define IP_TUNNEL_INFO_IPV6	0x02	/* key contains IPv6 addresses */
+
+/* Maximum tunnel options length. */
+#define IP_TUNNEL_OPTS_MAX					\
+	GENMASK((FIELD_SIZEOF(struct ip_tunnel_info,		\
+			      options_len) * BITS_PER_BYTE) - 1, 0)
 
 struct ip_tunnel_info {
 	struct ip_tunnel_key	key;

net/core/filter.c

···
 	.arg4_type	= ARG_ANYTHING,
 };
 
-#define BPF_TUNLEN_MAX	255
-
 static u64 bpf_skb_set_tunnel_opt(u64 r1, u64 r2, u64 size, u64 r4, u64 r5)
 {
 	struct sk_buff *skb = (struct sk_buff *) (long) r1;
···
 
 	if (unlikely(info != &md->u.tun_info || (size & (sizeof(u32) - 1))))
 		return -EINVAL;
-	if (unlikely(size > BPF_TUNLEN_MAX))
+	if (unlikely(size > IP_TUNNEL_OPTS_MAX))
 		return -ENOMEM;
 
 	ip_tunnel_info_opts_set(info, from, size);
···
 bpf_get_skb_set_tunnel_proto(enum bpf_func_id which)
 {
 	if (!md_dst) {
-		BUILD_BUG_ON(FIELD_SIZEOF(struct ip_tunnel_info,
-					  options_len) != 1);
-
 		/* Race is not possible, since it's called from verifier
 		 * that is holding verifier mutex.
 		 */
-		md_dst = metadata_dst_alloc_percpu(BPF_TUNLEN_MAX,
+		md_dst = metadata_dst_alloc_percpu(IP_TUNNEL_OPTS_MAX,
 						   GFP_KERNEL);
 		if (!md_dst)
 			return NULL;

net/ipv4/ip_tunnel_core.c

···
 
 void __init ip_tunnel_core_init(void)
 {
+	/* If you land here, make sure whether increasing ip_tunnel_info's
+	 * options_len is a reasonable choice with its usage in front ends
+	 * (f.e., it's part of flow keys, etc).
+	 */
+	BUILD_BUG_ON(IP_TUNNEL_OPTS_MAX != 255);
+
 	lwtunnel_encap_add_ops(&ip_tun_lwt_ops, LWTUNNEL_ENCAP_IP);
 	lwtunnel_encap_add_ops(&ip6_tun_lwt_ops, LWTUNNEL_ENCAP_IP6);
 }

net/openvswitch/flow.h

···
 	FIELD_SIZEOF(struct sw_flow_key, recirc_id))
 
 struct sw_flow_key {
-	u8 tun_opts[255];
+	u8 tun_opts[IP_TUNNEL_OPTS_MAX];
 	u8 tun_opts_len;
 	struct ip_tunnel_key tun_key;	/* Encapsulating tunnel key. */
 	struct {