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bpf: Add BPF_MAP_GET_FD_BY_ID

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Add BPF_MAP_GET_FD_BY_ID command to allow user to get a fd
from a bpf_map's ID.

bpf_map_inc_not_zero() is added and is called with map_idr_lock
held.

__bpf_map_put() is also added which has the 'bool do_idr_lock'
param to decide if the map_idr_lock should be acquired when
freeing the map->id.

In the error path of bpf_map_inc_not_zero(), it may have to
call __bpf_map_put(map, false) which does not need
to take the map_idr_lock when freeing the map->id.

It is currently limited to CAP_SYS_ADMIN which we can
consider to lift it in followup patches.

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Acked-by: Alexei Starovoitov <ast@fb.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Martin KaFai Lau 2017-06-05 12:15:50 -07:00 committed by David S. Miller
parent b16d9aa4c2
commit bd5f5f4ecb
2 changed files with 87 additions and 10 deletions
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2
include/uapi/linux/bpf.h
View File

@ -85,6 +85,7 @@ enum bpf_cmd {
BPF_PROG_GET_NEXT_ID,
BPF_MAP_GET_NEXT_ID,
BPF_PROG_GET_FD_BY_ID,
BPF_MAP_GET_FD_BY_ID,
};
enum bpf_map_type {
@ -217,6 +218,7 @@ union bpf_attr {
union {
__u32 start_id;
__u32 prog_id;
__u32 map_id;
};
__u32 next_id;
};

95
kernel/bpf/syscall.c
View File

@ -135,11 +135,19 @@ static int bpf_map_alloc_id(struct bpf_map *map)
return id > 0 ? 0 : id;
}
static void bpf_map_free_id(struct bpf_map *map)
static void bpf_map_free_id(struct bpf_map *map, bool do_idr_lock)
{
spin_lock_bh(&map_idr_lock);
if (do_idr_lock)
spin_lock_bh(&map_idr_lock);
else
__acquire(&map_idr_lock);
idr_remove(&map_idr, map->id);
spin_unlock_bh(&map_idr_lock);
if (do_idr_lock)
spin_unlock_bh(&map_idr_lock);
else
__release(&map_idr_lock);
}
/* called from workqueue */
@ -163,16 +171,21 @@ static void bpf_map_put_uref(struct bpf_map *map)
/* decrement map refcnt and schedule it for freeing via workqueue
* (unrelying map implementation ops->map_free() might sleep)
*/
void bpf_map_put(struct bpf_map *map)
static void __bpf_map_put(struct bpf_map *map, bool do_idr_lock)
{
if (atomic_dec_and_test(&map->refcnt)) {
/* bpf_map_free_id() must be called first */
bpf_map_free_id(map);
bpf_map_free_id(map, do_idr_lock);
INIT_WORK(&map->work, bpf_map_free_deferred);
schedule_work(&map->work);
}
}
void bpf_map_put(struct bpf_map *map)
{
__bpf_map_put(map, true);
}
void bpf_map_put_with_uref(struct bpf_map *map)
{
bpf_map_put_uref(map);
@ -271,15 +284,20 @@ static int map_create(union bpf_attr *attr)
goto free_map;
err = bpf_map_new_fd(map);
if (err < 0)
/* failed to allocate fd */
goto free_id;
if (err < 0) {
/* failed to allocate fd.
* bpf_map_put() is needed because the above
* bpf_map_alloc_id() has published the map
* to the userspace and the userspace may
* have refcnt-ed it through BPF_MAP_GET_FD_BY_ID.
*/
bpf_map_put(map);
return err;
}
trace_bpf_map_create(map, err);
return err;
free_id:
bpf_map_free_id(map);
free_map:
bpf_map_uncharge_memlock(map);
free_map_nouncharge:
@ -331,6 +349,28 @@ struct bpf_map *bpf_map_get_with_uref(u32 ufd)
return map;
}
/* map_idr_lock should have been held */
static struct bpf_map *bpf_map_inc_not_zero(struct bpf_map *map,
bool uref)
{
int refold;
refold = __atomic_add_unless(&map->refcnt, 1, 0);
if (refold >= BPF_MAX_REFCNT) {
__bpf_map_put(map, false);
return ERR_PTR(-EBUSY);
}
if (!refold)
return ERR_PTR(-ENOENT);
if (uref)
atomic_inc(&map->usercnt);
return map;
}
int __weak bpf_stackmap_copy(struct bpf_map *map, void *key, void *value)
{
return -ENOTSUPP;
@ -1167,6 +1207,38 @@ static int bpf_prog_get_fd_by_id(const union bpf_attr *attr)
return fd;
}
#define BPF_MAP_GET_FD_BY_ID_LAST_FIELD map_id
static int bpf_map_get_fd_by_id(const union bpf_attr *attr)
{
struct bpf_map *map;
u32 id = attr->map_id;
int fd;
if (CHECK_ATTR(BPF_MAP_GET_FD_BY_ID))
return -EINVAL;
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
spin_lock_bh(&map_idr_lock);
map = idr_find(&map_idr, id);
if (map)
map = bpf_map_inc_not_zero(map, true);
else
map = ERR_PTR(-ENOENT);
spin_unlock_bh(&map_idr_lock);
if (IS_ERR(map))
return PTR_ERR(map);
fd = bpf_map_new_fd(map);
if (fd < 0)
bpf_map_put(map);
return fd;
}
SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, size)
{
union bpf_attr attr = {};
@ -1255,6 +1327,9 @@ SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, siz
case BPF_PROG_GET_FD_BY_ID:
err = bpf_prog_get_fd_by_id(&attr);
break;
case BPF_MAP_GET_FD_BY_ID:
err = bpf_map_get_fd_by_id(&attr);
break;
default:
err = -EINVAL;
break;