bpf: implement bpf_get_current_cgroup_id() helper

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>

3 files changed, 18 insertions, 0 deletions

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 527587de8a67..9f1493705f40 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1765,6 +1765,7 @@ const struct bpf_func_proto bpf_get_current_uid_gid_proto __weak;
 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)
 {
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 3d24e238221e..73065e2d23c2 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -179,3 +179,18 @@ const struct bpf_func_proto bpf_get_current_comm_proto = {
 	.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
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 752992ce3513..e2ab5b7f29d2 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -564,6 +564,8 @@ tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 		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;
 	}