From: Daniel Borkmann <daniel@iogearbox.net>
Date: Sat, 2 Jun 2018 23:06:36 +0200
Subject: bpf: add bpf_skb_cgroup_id helper
Patch-mainline: v4.18-rc1
Git-commit: cb20b08ead401fd17627a36f035c0bf5bfee5567
References: bsc#1109837

Add a new bpf_skb_cgroup_id() helper that allows to retrieve the
cgroup id from the skb's socket. This is useful in particular to
enable bpf_get_cgroup_classid()-like behavior for cgroup v1 in
cgroup v2 by allowing ID based matching on egress. This can in
particular be used in combination with applying policy e.g. from
map lookups, and also complements the older bpf_skb_under_cgroup()
interface. In user space the cgroup id for a given path can be
retrieved through the f_handle as demonstrated in [0] recently.

  [0] https://lkml.org/lkml/2018/5/22/1190

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 include/uapi/linux/bpf.h |   19 ++++++++++++++++++-
 net/core/filter.c        |   25 +++++++++++++++++++++++++
 2 files changed, 43 insertions(+), 1 deletion(-)

--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -847,6 +847,22 @@ union bpf_attr {
  *		egress otherwise). This is the only flag supported for now.
  *	Return
  *		**SK_PASS** on success, or **SK_DROP** on error.
+ *
+ * uint64_t bpf_skb_cgroup_id(struct sk_buff *skb)
+ * 	Description
+ * 		Return the cgroup v2 id of the socket associated with the *skb*.
+ * 		This is roughly similar to the **bpf_get_cgroup_classid**\ ()
+ * 		helper for cgroup v1 by providing a tag resp. identifier that
+ * 		can be matched on or used for map lookups e.g. to implement
+ * 		policy. The cgroup v2 id of a given path in the hierarchy is
+ * 		exposed in user space through the f_handle API in order to get
+ * 		to the same 64-bit id.
+ *
+ * 		This helper can be used on TC egress path, but not on ingress,
+ * 		and is available only if the kernel was compiled with the
+ * 		**CONFIG_SOCK_CGROUP_DATA** configuration option.
+ * 	Return
+ * 		The id is returned or 0 in case the id could not be retrieved.
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -918,7 +934,8 @@ union bpf_attr {
 	FN(skb_load_bytes_relative),	\
 	FN(sock_hash_update),		\
 	FN(msg_redirect_hash),		\
-	FN(sk_redirect_hash),
+	FN(sk_redirect_hash),		\
+	FN(skb_cgroup_id),
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
  * function eBPF program intends to call
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -3661,6 +3661,27 @@ static const struct bpf_func_proto bpf_s
 	.arg3_type	= ARG_ANYTHING,
 };
 
+#ifdef CONFIG_SOCK_CGROUP_DATA
+BPF_CALL_1(bpf_skb_cgroup_id, const struct sk_buff *, skb)
+{
+	struct sock *sk = skb_to_full_sk(skb);
+	struct cgroup *cgrp;
+
+	if (!sk || !sk_fullsock(sk))
+		return 0;
+
+	cgrp = sock_cgroup_ptr(&sk->sk_cgrp_data);
+	return cgrp->kn->id.id;
+}
+
+static const struct bpf_func_proto bpf_skb_cgroup_id_proto = {
+	.func           = bpf_skb_cgroup_id,
+	.gpl_only       = false,
+	.ret_type       = RET_INTEGER,
+	.arg1_type      = ARG_PTR_TO_CTX,
+};
+#endif
+
 static unsigned long bpf_xdp_copy(void *dst_buff, const void *src_buff,
 				  unsigned long off, unsigned long len)
 {
@@ -4131,6 +4152,10 @@ sk_filter_func_proto(enum bpf_func_id fu
 	case BPF_FUNC_skb_get_xfrm_state:
 		return &bpf_skb_get_xfrm_state_proto;
 #endif
+#ifdef CONFIG_SOCK_CGROUP_DATA
+	case BPF_FUNC_skb_cgroup_id:
+		return &bpf_skb_cgroup_id_proto;
+#endif
 	default:
 		return bpf_base_func_proto(func_id);
 	}