bpf: add helper for getting xfrm states

This commit introduces a helper which allows fetching xfrm state
parameters by eBPF programs attached to TC.

Prototype:
bpf_skb_get_xfrm_state(skb, index, xfrm_state, size, flags)

skb: pointer to skb
index: the index in the skb xfrm_state secpath array
xfrm_state: pointer to 'struct bpf_xfrm_state'
size: size of 'struct bpf_xfrm_state'
flags: reserved for future extensions

The helper returns 0 on success. Non zero if no xfrm state at the index
is found - or non exists at all.

struct bpf_xfrm_state currently includes the SPI, peer IPv4/IPv6
address and the reqid; it can be further extended by adding elements to
its end - indicating the populated fields by the 'size' argument -
keeping backwards compatibility.

Typical usage:

struct bpf_xfrm_state x = {};
bpf_skb_get_xfrm_state(skb, 0, &x, sizeof(x), 0);
...

Signed-off-by: Eyal Birger <eyal.birger@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

1 files changed, 48 insertions, 0 deletions

diff --git a/net/core/filter.c b/net/core/filter.c
index e25bc4a3aa1a..8e45c6c7ab08 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -57,6 +57,7 @@
 #include <net/sock_reuseport.h>
 #include <net/busy_poll.h>
 #include <net/tcp.h>
+#include <net/xfrm.h>
 #include <linux/bpf_trace.h>
 
 /**
@@ -3743,6 +3744,49 @@ static const struct bpf_func_proto bpf_bind_proto = {
 	.arg3_type	= ARG_CONST_SIZE,
 };
 
+#ifdef CONFIG_XFRM
+BPF_CALL_5(bpf_skb_get_xfrm_state, struct sk_buff *, skb, u32, index,
+	   struct bpf_xfrm_state *, to, u32, size, u64, flags)
+{
+	const struct sec_path *sp = skb_sec_path(skb);
+	const struct xfrm_state *x;
+
+	if (!sp || unlikely(index >= sp->len || flags))
+		goto err_clear;
+
+	x = sp->xvec[index];
+
+	if (unlikely(size != sizeof(struct bpf_xfrm_state)))
+		goto err_clear;
+
+	to->reqid = x->props.reqid;
+	to->spi = x->id.spi;
+	to->family = x->props.family;
+	if (to->family == AF_INET6) {
+		memcpy(to->remote_ipv6, x->props.saddr.a6,
+		       sizeof(to->remote_ipv6));
+	} else {
+		to->remote_ipv4 = x->props.saddr.a4;
+	}
+
+	return 0;
+err_clear:
+	memset(to, 0, size);
+	return -EINVAL;
+}
+
+static const struct bpf_func_proto bpf_skb_get_xfrm_state_proto = {
+	.func		= bpf_skb_get_xfrm_state,
+	.gpl_only	= false,
+	.ret_type	= RET_INTEGER,
+	.arg1_type	= ARG_PTR_TO_CTX,
+	.arg2_type	= ARG_ANYTHING,
+	.arg3_type	= ARG_PTR_TO_UNINIT_MEM,
+	.arg4_type	= ARG_CONST_SIZE,
+	.arg5_type	= ARG_ANYTHING,
+};
+#endif
+
 static const struct bpf_func_proto *
 bpf_base_func_proto(enum bpf_func_id func_id)
 {
@@ -3884,6 +3928,10 @@ tc_cls_act_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 		return &bpf_get_socket_cookie_proto;
 	case BPF_FUNC_get_socket_uid:
 		return &bpf_get_socket_uid_proto;
+#ifdef CONFIG_XFRM
+	case BPF_FUNC_skb_get_xfrm_state:
+		return &bpf_skb_get_xfrm_state_proto;
+#endif
 	default:
 		return bpf_base_func_proto(func_id);
 	}