From: Yonghong Song <yhs@fb.com>
Date: Sun, 3 Jun 2018 15:59:41 -0700
Subject: bpf: implement bpf_get_current_cgroup_id() helper
Patch-mainline: v4.18-rc1
Git-commit: bf6fa2c893c5237b48569a13fa3c673041430b6c
References: bsc#1109837

bpf has been used extensively for tracing. For example, bcc
contains an almost full set of bpf-based tools to trace kernel
and user functions/events. Most tracing tools are currently
either filtered based on pid or system-wide.

Containers have been used quite extensively in industry and
cgroup is often used together to provide resource isolation
and protection. Several processes may run inside the same
container. It is often desirable to get container-level tracing
results as well, e.g. syscall count, function count, I/O
activity, etc.

This patch implements a new helper, bpf_get_current_cgroup_id(),
which will return cgroup id based on the cgroup within which
the current task is running.

The later patch will provide an example to show that
userspace can get the same cgroup id so it could
configure a filter or policy in the bpf program based on
task cgroup id.

The helper is currently implemented for tracing. It can
be added to other program types as well when needed.

Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 include/linux/bpf.h      |    1 +
 include/uapi/linux/bpf.h |    8 +++++++-
 kernel/bpf/core.c        |    1 +
 kernel/bpf/helpers.c     |   15 +++++++++++++++
 kernel/trace/bpf_trace.c |    2 ++
 5 files changed, 26 insertions(+), 1 deletion(-)

--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -740,6 +740,7 @@ extern const struct bpf_func_proto bpf_g
 extern const struct bpf_func_proto bpf_get_stack_proto;
 extern const struct bpf_func_proto bpf_sock_map_update_proto;
 extern const struct bpf_func_proto bpf_sock_hash_update_proto;
+extern const struct bpf_func_proto bpf_get_current_cgroup_id_proto;
 
 /* Shared helpers among cBPF and eBPF. */
 void bpf_user_rnd_init_once(void);
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -1892,6 +1892,11 @@ union bpf_attr {
  * 		**CONFIG_SOCK_CGROUP_DATA** configuration option.
  * 	Return
  * 		The id is returned or 0 in case the id could not be retrieved.
+ *
+ * u64 bpf_get_current_cgroup_id(void)
+ * 	Return
+ * 		A 64-bit integer containing the current cgroup id based
+ * 		on the cgroup within which the current task is running.
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -1965,7 +1970,8 @@ union bpf_attr {
 	FN(sock_hash_update),		\
 	FN(msg_redirect_hash),		\
 	FN(sk_redirect_hash),		\
-	FN(skb_cgroup_id),
+	FN(skb_cgroup_id),		\
+	FN(get_current_cgroup_id),
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
  * function eBPF program intends to call
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1761,6 +1761,7 @@ const struct bpf_func_proto bpf_get_curr
 const struct bpf_func_proto bpf_get_current_comm_proto __weak;
 const struct bpf_func_proto bpf_sock_map_update_proto __weak;
 const struct bpf_func_proto bpf_sock_hash_update_proto __weak;
+const struct bpf_func_proto bpf_get_current_cgroup_id_proto __weak;
 
 const struct bpf_func_proto * __weak bpf_get_trace_printk_proto(void)
 {
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -179,3 +179,18 @@ const struct bpf_func_proto bpf_get_curr
 	.arg1_type	= ARG_PTR_TO_UNINIT_MEM,
 	.arg2_type	= ARG_CONST_SIZE,
 };
+
+#ifdef CONFIG_CGROUPS
+BPF_CALL_0(bpf_get_current_cgroup_id)
+{
+	struct cgroup *cgrp = task_dfl_cgroup(current);
+
+	return cgrp->kn->id.id;
+}
+
+const struct bpf_func_proto bpf_get_current_cgroup_id_proto = {
+	.func		= bpf_get_current_cgroup_id,
+	.gpl_only	= false,
+	.ret_type	= RET_INTEGER,
+};
+#endif
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -542,6 +542,8 @@ tracing_func_proto(enum bpf_func_id func
 		return &bpf_get_prandom_u32_proto;
 	case BPF_FUNC_probe_read_str:
 		return &bpf_probe_read_str_proto;
+	case BPF_FUNC_get_current_cgroup_id:
+		return &bpf_get_current_cgroup_id_proto;
 	default:
 		return NULL;
 	}