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

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On 12/13/23 6:38 AM, Michael Weiß wrote:
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@xxxxxxxxxxxxxxxxxxx>
Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@xxxxxxxxxxxxx>
---
  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]);

This seems wrong here. The cgrp could become invalid once leaving
rcu critical section.

+	return array != &bpf_empty_prog_array.hdr;

I guess you need include 'array' usage as well in the rcu cs.
So overall should look like:

	rcu_read_lock();
	cgrp = task_dfl_cgroup(current);
	array = rcu_access_pointer(cgrp->bpf.effective[type]);
	bpf_prog_exists = array != &bpf_empty_prog_array.hdr;
	rcu_read_unlock();

	return bpf_prog_exists;

+}
+EXPORT_SYMBOL(cgroup_bpf_current_enabled);
+
  /* __always_inline is necessary to prevent indirect call through run_prog
   * function pointer.
   */




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