[RFC PATCH v3 1/3] bpf: cgroup: Introduce helper cgroup_bpf_current_enabled()

["Michael Weiß" <michael.weiss@aisec.fraunhofer.de>]

This helper can be used to check if a cgroup-bpf specific program is
active for the current task.

Signed-off-by: Michael Weiß <michael.weiss@aisec.fraunhofer.de>
Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
---
 include/linux/bpf-cgroup.h |  2 ++
 kernel/bpf/cgroup.c        | 14 ++++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/include/linux/bpf-cgroup.h b/include/linux/bpf-cgroup.h
index a789266feac3..7cb49bde09ff 100644
--- a/include/linux/bpf-cgroup.h
+++ b/include/linux/bpf-cgroup.h
@@ -191,6 +191,8 @@ static inline bool cgroup_bpf_sock_enabled(struct sock *sk,
 	return array != &bpf_empty_prog_array.hdr;
 }
 
+bool cgroup_bpf_current_enabled(enum cgroup_bpf_attach_type type);
+
 /* Wrappers for __cgroup_bpf_run_filter_skb() guarded by cgroup_bpf_enabled. */
 #define BPF_CGROUP_RUN_PROG_INET_INGRESS(sk, skb)			      \
 ({									      \
diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
index 491d20038cbe..9007165abe8c 100644
--- a/kernel/bpf/cgroup.c
+++ b/kernel/bpf/cgroup.c
@@ -24,6 +24,20 @@
 DEFINE_STATIC_KEY_ARRAY_FALSE(cgroup_bpf_enabled_key, MAX_CGROUP_BPF_ATTACH_TYPE);
 EXPORT_SYMBOL(cgroup_bpf_enabled_key);
 
+bool cgroup_bpf_current_enabled(enum cgroup_bpf_attach_type type)
+{
+	struct cgroup *cgrp;
+	struct bpf_prog_array *array;
+
+	rcu_read_lock();
+	cgrp = task_dfl_cgroup(current);
+	rcu_read_unlock();
+
+	array = rcu_access_pointer(cgrp->bpf.effective[type]);
+	return array != &bpf_empty_prog_array.hdr;
+}
+EXPORT_SYMBOL(cgroup_bpf_current_enabled);
+
 /* __always_inline is necessary to prevent indirect call through run_prog
  * function pointer.
  */
-- 
2.30.2