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Commit dbcc1ba2 authored by Stanislav Fomichev's avatar Stanislav Fomichev Committed by Daniel Borkmann
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bpf: cgroup: properly use bpf_prog_array api 



Now that we don't have __rcu markers on the bpf_prog_array helpers,
let's use proper rcu_dereference_protected to obtain array pointer
under mutex.

We also don't need __rcu annotations on cgroup_bpf.inactive since
it's not read/updated concurrently.

v4:
* drop cgroup_rcu_xyz wrappers and use rcu APIs directly; presumably
  should be more clear to understand which mutex/refcount protects
  each particular place

v3:
* amend cgroup_rcu_dereference to include percpu_ref_is_dying;
  cgroup_bpf is now reference counted and we don't hold cgroup_mutex
  anymore in cgroup_bpf_release

v2:
* replace xchg with rcu_swap_protected

Cc: Roman Gushchin <guro@fb.com>
Signed-off-by: default avatarStanislav Fomichev <sdf@google.com>
Acked-by: default avatarRoman Gushchin <guro@fb.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
parent 02205d2e

include/linux/bpf-cgroup.h

+1 −1
Original line number Diff line number Diff line
@@ -72,7 +72,7 @@ struct cgroup_bpf { 
	u32 flags[MAX_BPF_ATTACH_TYPE];



	/* temp storage for effective prog array used by prog_attach/detach */

	struct bpf_prog_array __rcu *inactive;

	struct bpf_prog_array *inactive;



	/* reference counter used to detach bpf programs after cgroup removal */

	struct percpu_ref refcnt;

kernel/bpf/cgroup.c

+17 −11
Original line number Diff line number Diff line
@@ -38,6 +38,7 @@ static void cgroup_bpf_release(struct work_struct *work) 
	struct cgroup *cgrp = container_of(work, struct cgroup,

					   bpf.release_work);

	enum bpf_cgroup_storage_type stype;

	struct bpf_prog_array *old_array;

	unsigned int type;



	for (type = 0; type < ARRAY_SIZE(cgrp->bpf.progs); type++) {
@@ -54,7 +55,10 @@ static void cgroup_bpf_release(struct work_struct *work) 
			kfree(pl);

			static_branch_dec(&cgroup_bpf_enabled_key);

		}

		bpf_prog_array_free(cgrp->bpf.effective[type]);

		old_array = rcu_dereference_protected(

				cgrp->bpf.effective[type],

				percpu_ref_is_dying(&cgrp->bpf.refcnt));

		bpf_prog_array_free(old_array);

	}



	percpu_ref_exit(&cgrp->bpf.refcnt);
@@ -126,7 +130,7 @@ static bool hierarchy_allows_attach(struct cgroup *cgrp, 
 */

static int compute_effective_progs(struct cgroup *cgrp,

				   enum bpf_attach_type type,

				   struct bpf_prog_array __rcu **array)

				   struct bpf_prog_array **array)

{

	enum bpf_cgroup_storage_type stype;

	struct bpf_prog_array *progs;
@@ -164,17 +168,16 @@ static int compute_effective_progs(struct cgroup *cgrp, 
		}

	} while ((p = cgroup_parent(p)));



	rcu_assign_pointer(*array, progs);

	*array = progs;

	return 0;

}



static void activate_effective_progs(struct cgroup *cgrp,

				     enum bpf_attach_type type,

				     struct bpf_prog_array __rcu *array)

				     struct bpf_prog_array *old_array)

{

	struct bpf_prog_array __rcu *old_array;



	old_array = xchg(&cgrp->bpf.effective[type], array);

	rcu_swap_protected(cgrp->bpf.effective[type], old_array,

			   lockdep_is_held(&cgroup_mutex));

	/* free prog array after grace period, since __cgroup_bpf_run_*()

	 * might be still walking the array

	 */
@@ -191,7 +194,7 @@ int cgroup_bpf_inherit(struct cgroup *cgrp) 
 * that array below is variable length

 */

#define	NR ARRAY_SIZE(cgrp->bpf.effective)

	struct bpf_prog_array __rcu *arrays[NR] = {};

	struct bpf_prog_array *arrays[NR] = {};

	int ret, i;



	ret = percpu_ref_init(&cgrp->bpf.refcnt, cgroup_bpf_release_fn, 0,
@@ -477,10 +480,14 @@ int __cgroup_bpf_query(struct cgroup *cgrp, const union bpf_attr *attr, 
	enum bpf_attach_type type = attr->query.attach_type;

	struct list_head *progs = &cgrp->bpf.progs[type];

	u32 flags = cgrp->bpf.flags[type];

	struct bpf_prog_array *effective;

	int cnt, ret = 0, i;



	effective = rcu_dereference_protected(cgrp->bpf.effective[type],

					      lockdep_is_held(&cgroup_mutex));



	if (attr->query.query_flags & BPF_F_QUERY_EFFECTIVE)

		cnt = bpf_prog_array_length(cgrp->bpf.effective[type]);

		cnt = bpf_prog_array_length(effective);

	else

		cnt = prog_list_length(progs);
@@ -497,8 +504,7 @@ int __cgroup_bpf_query(struct cgroup *cgrp, const union bpf_attr *attr, 
	}



	if (attr->query.query_flags & BPF_F_QUERY_EFFECTIVE) {

		return bpf_prog_array_copy_to_user(cgrp->bpf.effective[type],

						   prog_ids, cnt);

		return bpf_prog_array_copy_to_user(effective, prog_ids, cnt);

	} else {

		struct bpf_prog_list *pl;

		u32 id;