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bpf: remove __rcu annotations from bpf_prog_array

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Drop __rcu annotations and rcu read sections from bpf_prog_array
helper functions. They are not needed since all existing callers
call those helpers from the rcu update side while holding a mutex.
This guarantees that use-after-free could not happen.

In the next patches I'll fix the callers with missing
rcu_dereference_protected to make sparse/lockdep happy, the proper
way to use these helpers is:

	struct bpf_prog_array __rcu *progs = ...;
	struct bpf_prog_array *p;

	mutex_lock(&mtx);
	p = rcu_dereference_protected(progs, lockdep_is_held(&mtx));
	bpf_prog_array_length(p);
	bpf_prog_array_copy_to_user(p, ...);
	bpf_prog_array_delete_safe(p, ...);
	bpf_prog_array_copy_info(p, ...);
	bpf_prog_array_copy(p, ...);
	bpf_prog_array_free(p);
	mutex_unlock(&mtx);

No functional changes! rcu_dereference_protected with lockdep_is_held
should catch any cases where we update prog array without a mutex
(I've looked at existing call sites and I think we hold a mutex
everywhere).

Motivation is to fix sparse warnings:
kernel/bpf/core.c:1803:9: warning: incorrect type in argument 1 (different address spaces)
kernel/bpf/core.c:1803:9:    expected struct callback_head *head
kernel/bpf/core.c:1803:9:    got struct callback_head [noderef] <asn:4> *
kernel/bpf/core.c:1877:44: warning: incorrect type in initializer (different address spaces)
kernel/bpf/core.c:1877:44:    expected struct bpf_prog_array_item *item
kernel/bpf/core.c:1877:44:    got struct bpf_prog_array_item [noderef] <asn:4> *
kernel/bpf/core.c:1901:26: warning: incorrect type in assignment (different address spaces)
kernel/bpf/core.c:1901:26:    expected struct bpf_prog_array_item *existing
kernel/bpf/core.c:1901:26:    got struct bpf_prog_array_item [noderef] <asn:4> *
kernel/bpf/core.c:1935:26: warning: incorrect type in assignment (different address spaces)
kernel/bpf/core.c:1935:26:    expected struct bpf_prog_array_item *[assigned] existing
kernel/bpf/core.c:1935:26:    got struct bpf_prog_array_item [noderef] <asn:4> *

v2:
* remove comment about potential race; that can't happen
  because all callers are in rcu-update section

Cc: Roman Gushchin <guro@fb.com>
Acked-by: Roman Gushchin <guro@fb.com>
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
This commit is contained in:
Stanislav Fomichev 2019-05-28 14:14:41 -07:00 committed by Daniel Borkmann
parent fe937ea12e
commit 54e9c9d4b5
2 changed files with 19 additions and 30 deletions
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12
include/linux/bpf.h
View File

@ -514,17 +514,17 @@ struct bpf_prog_array {
};
struct bpf_prog_array *bpf_prog_array_alloc(u32 prog_cnt, gfp_t flags);
void bpf_prog_array_free(struct bpf_prog_array __rcu *progs);
int bpf_prog_array_length(struct bpf_prog_array __rcu *progs);
int bpf_prog_array_copy_to_user(struct bpf_prog_array __rcu *progs,
void bpf_prog_array_free(struct bpf_prog_array *progs);
int bpf_prog_array_length(struct bpf_prog_array *progs);
int bpf_prog_array_copy_to_user(struct bpf_prog_array *progs,
__u32 __user *prog_ids, u32 cnt);
void bpf_prog_array_delete_safe(struct bpf_prog_array __rcu *progs,
void bpf_prog_array_delete_safe(struct bpf_prog_array *progs,
struct bpf_prog *old_prog);
int bpf_prog_array_copy_info(struct bpf_prog_array __rcu *array,
int bpf_prog_array_copy_info(struct bpf_prog_array *array,
u32 *prog_ids, u32 request_cnt,
u32 *prog_cnt);
int bpf_prog_array_copy(struct bpf_prog_array __rcu *old_array,
int bpf_prog_array_copy(struct bpf_prog_array *old_array,
struct bpf_prog *exclude_prog,
struct bpf_prog *include_prog,
struct bpf_prog_array **new_array);

37
kernel/bpf/core.c
View File

@ -1795,38 +1795,33 @@ struct bpf_prog_array *bpf_prog_array_alloc(u32 prog_cnt, gfp_t flags)
return &empty_prog_array.hdr;
}
void bpf_prog_array_free(struct bpf_prog_array __rcu *progs)
void bpf_prog_array_free(struct bpf_prog_array *progs)
{
if (!progs ||
progs == (struct bpf_prog_array __rcu *)&empty_prog_array.hdr)
if (!progs || progs == &empty_prog_array.hdr)
return;
kfree_rcu(progs, rcu);
}
int bpf_prog_array_length(struct bpf_prog_array __rcu *array)
int bpf_prog_array_length(struct bpf_prog_array *array)
{
struct bpf_prog_array_item *item;
u32 cnt = 0;
rcu_read_lock();
item = rcu_dereference(array)->items;
for (; item->prog; item++)
for (item = array->items; item->prog; item++)
if (item->prog != &dummy_bpf_prog.prog)
cnt++;
rcu_read_unlock();
return cnt;
}
static bool bpf_prog_array_copy_core(struct bpf_prog_array __rcu *array,
static bool bpf_prog_array_copy_core(struct bpf_prog_array *array,
u32 *prog_ids,
u32 request_cnt)
{
struct bpf_prog_array_item *item;
int i = 0;
item = rcu_dereference_check(array, 1)->items;
for (; item->prog; item++) {
for (item = array->items; item->prog; item++) {
if (item->prog == &dummy_bpf_prog.prog)
continue;
prog_ids[i] = item->prog->aux->id;
@ -1839,7 +1834,7 @@ static bool bpf_prog_array_copy_core(struct bpf_prog_array __rcu *array,
return !!(item->prog);
}
int bpf_prog_array_copy_to_user(struct bpf_prog_array __rcu *array,
int bpf_prog_array_copy_to_user(struct bpf_prog_array *array,
__u32 __user *prog_ids, u32 cnt)
{
unsigned long err = 0;
@ -1850,18 +1845,12 @@ int bpf_prog_array_copy_to_user(struct bpf_prog_array __rcu *array,
* cnt = bpf_prog_array_length();
* if (cnt > 0)
* bpf_prog_array_copy_to_user(..., cnt);
* so below kcalloc doesn't need extra cnt > 0 check, but
* bpf_prog_array_length() releases rcu lock and
* prog array could have been swapped with empty or larger array,
* so always copy 'cnt' prog_ids to the user.
* In a rare race the user will see zero prog_ids
* so below kcalloc doesn't need extra cnt > 0 check.
*/
ids = kcalloc(cnt, sizeof(u32), GFP_USER | __GFP_NOWARN);
if (!ids)
return -ENOMEM;
rcu_read_lock();
nospc = bpf_prog_array_copy_core(array, ids, cnt);
rcu_read_unlock();
err = copy_to_user(prog_ids, ids, cnt * sizeof(u32));
kfree(ids);
if (err)
@ -1871,19 +1860,19 @@ int bpf_prog_array_copy_to_user(struct bpf_prog_array __rcu *array,
return 0;
}
void bpf_prog_array_delete_safe(struct bpf_prog_array __rcu *array,
void bpf_prog_array_delete_safe(struct bpf_prog_array *array,
struct bpf_prog *old_prog)
{
struct bpf_prog_array_item *item = array->items;
struct bpf_prog_array_item *item;
for (; item->prog; item++)
for (item = array->items; item->prog; item++)
if (item->prog == old_prog) {
WRITE_ONCE(item->prog, &dummy_bpf_prog.prog);
break;
}
}
int bpf_prog_array_copy(struct bpf_prog_array __rcu *old_array,
int bpf_prog_array_copy(struct bpf_prog_array *old_array,
struct bpf_prog *exclude_prog,
struct bpf_prog *include_prog,
struct bpf_prog_array **new_array)
@ -1947,7 +1936,7 @@ int bpf_prog_array_copy(struct bpf_prog_array __rcu *old_array,
return 0;
}
int bpf_prog_array_copy_info(struct bpf_prog_array __rcu *array,
int bpf_prog_array_copy_info(struct bpf_prog_array *array,
u32 *prog_ids, u32 request_cnt,
u32 *prog_cnt)
{