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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: Stanislav Fomichev <sdf@google.com>
Acked-by: Roman Gushchin <guro@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
This commit is contained in:
Stanislav Fomichev 2019-05-28 14:14:43 -07:00 committed by Daniel Borkmann
parent 02205d2ed6
commit dbcc1ba26e
2 changed files with 18 additions and 12 deletions
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2
include/linux/bpf-cgroup.h
View File

@ -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;

28
kernel/bpf/cgroup.c
View File

@ -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;