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Commit bd5f5f4e authored by Martin KaFai Lau's avatar Martin KaFai Lau Committed by David S. Miller
Browse files

bpf: Add BPF_MAP_GET_FD_BY_ID 



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: default avatarMartin KaFai Lau <kafai@fb.com>
Acked-by: default avatarAlexei Starovoitov <ast@fb.com>
Acked-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent b16d9aa4

include/uapi/linux/bpf.h

+2 −0
Original line number Diff line number Diff line
@@ -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;

	};

kernel/bpf/syscall.c

+85 −10
Original line number Diff line number Diff line
@@ -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)

{

	if (do_idr_lock)

		spin_lock_bh(&map_idr_lock);

	else

		__acquire(&map_idr_lock);



	idr_remove(&map_idr, map->id);



	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;