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Commit b16d9aa4 authored by Martin KaFai Lau's avatar Martin KaFai Lau Committed by David S. Miller
Browse files

bpf: Add BPF_PROG_GET_FD_BY_ID 



Add BPF_PROG_GET_FD_BY_ID command to allow user to get a fd
from a bpf_prog's ID.

bpf_prog_inc_not_zero() is added and is called with prog_idr_lock
held.

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

In the error path of bpf_prog_inc_not_zero(), it may have to
call __bpf_prog_put(map, false) which does not need
to take the prog_idr_lock when freeing the prog->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 34ad5580

include/uapi/linux/bpf.h

+6 −2
Original line number Diff line number Diff line
@@ -84,6 +84,7 @@ enum bpf_cmd { 
	BPF_PROG_TEST_RUN,

	BPF_PROG_GET_NEXT_ID,

	BPF_MAP_GET_NEXT_ID,

	BPF_PROG_GET_FD_BY_ID,

};



enum bpf_map_type {
@@ -212,8 +213,11 @@ union bpf_attr { 
		__u32		duration;

	} test;



	struct { /* anonymous struct used by BPF_*_GET_NEXT_ID */

	struct { /* anonymous struct used by BPF_*_GET_*_ID */

		union {

			__u32		start_id;

			__u32		prog_id;

		};

		__u32		next_id;

	};

} __attribute__((aligned(8)));

kernel/bpf/syscall.c

+81 −10
Original line number Diff line number Diff line
@@ -703,15 +703,23 @@ static int bpf_prog_alloc_id(struct bpf_prog *prog) 
	return id > 0 ? 0 : id;

}



static void bpf_prog_free_id(struct bpf_prog *prog)

static void bpf_prog_free_id(struct bpf_prog *prog, bool do_idr_lock)

{

	/* cBPF to eBPF migrations are currently not in the idr store. */

	if (!prog->aux->id)

		return;



	if (do_idr_lock)

		spin_lock_bh(&prog_idr_lock);

	else

		__acquire(&prog_idr_lock);



	idr_remove(&prog_idr, prog->aux->id);



	if (do_idr_lock)

		spin_unlock_bh(&prog_idr_lock);

	else

		__release(&prog_idr_lock);

}



static void __bpf_prog_put_rcu(struct rcu_head *rcu)
@@ -723,16 +731,21 @@ static void __bpf_prog_put_rcu(struct rcu_head *rcu) 
	bpf_prog_free(aux->prog);

}



void bpf_prog_put(struct bpf_prog *prog)

static void __bpf_prog_put(struct bpf_prog *prog, bool do_idr_lock)

{

	if (atomic_dec_and_test(&prog->aux->refcnt)) {

		trace_bpf_prog_put_rcu(prog);

		/* bpf_prog_free_id() must be called first */

		bpf_prog_free_id(prog);

		bpf_prog_free_id(prog, do_idr_lock);

		bpf_prog_kallsyms_del(prog);

		call_rcu(&prog->aux->rcu, __bpf_prog_put_rcu);

	}

}



void bpf_prog_put(struct bpf_prog *prog)

{

	__bpf_prog_put(prog, true);

}

EXPORT_SYMBOL_GPL(bpf_prog_put);



static int bpf_prog_release(struct inode *inode, struct file *filp)
@@ -814,6 +827,24 @@ struct bpf_prog *bpf_prog_inc(struct bpf_prog *prog) 
}

EXPORT_SYMBOL_GPL(bpf_prog_inc);



/* prog_idr_lock should have been held */

static struct bpf_prog *bpf_prog_inc_not_zero(struct bpf_prog *prog)

{

	int refold;



	refold = __atomic_add_unless(&prog->aux->refcnt, 1, 0);



	if (refold >= BPF_MAX_REFCNT) {

		__bpf_prog_put(prog, false);

		return ERR_PTR(-EBUSY);

	}



	if (!refold)

		return ERR_PTR(-ENOENT);



	return prog;

}



static struct bpf_prog *__bpf_prog_get(u32 ufd, enum bpf_prog_type *type)

{

	struct fd f = fdget(ufd);
@@ -928,16 +959,21 @@ static int bpf_prog_load(union bpf_attr *attr) 
		goto free_used_maps;



	err = bpf_prog_new_fd(prog);

	if (err < 0)

		/* failed to allocate fd */

		goto free_id;

	if (err < 0) {

		/* failed to allocate fd.

		 * bpf_prog_put() is needed because the above

		 * bpf_prog_alloc_id() has published the prog

		 * to the userspace and the userspace may

		 * have refcnt-ed it through BPF_PROG_GET_FD_BY_ID.

		 */

		bpf_prog_put(prog);

		return err;

	}



	bpf_prog_kallsyms_add(prog);

	trace_bpf_prog_load(prog, err);

	return err;



free_id:

	bpf_prog_free_id(prog);

free_used_maps:

	free_used_maps(prog->aux);

free_prog:
@@ -1099,6 +1135,38 @@ static int bpf_obj_get_next_id(const union bpf_attr *attr, 
	return err;

}



#define BPF_PROG_GET_FD_BY_ID_LAST_FIELD prog_id



static int bpf_prog_get_fd_by_id(const union bpf_attr *attr)

{

	struct bpf_prog *prog;

	u32 id = attr->prog_id;

	int fd;



	if (CHECK_ATTR(BPF_PROG_GET_FD_BY_ID))

		return -EINVAL;



	if (!capable(CAP_SYS_ADMIN))

		return -EPERM;



	spin_lock_bh(&prog_idr_lock);

	prog = idr_find(&prog_idr, id);

	if (prog)

		prog = bpf_prog_inc_not_zero(prog);

	else

		prog = ERR_PTR(-ENOENT);

	spin_unlock_bh(&prog_idr_lock);



	if (IS_ERR(prog))

		return PTR_ERR(prog);



	fd = bpf_prog_new_fd(prog);

	if (fd < 0)

		bpf_prog_put(prog);



	return fd;

}



SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, size)

{

	union bpf_attr attr = {};
@@ -1184,6 +1252,9 @@ SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, siz 
		err = bpf_obj_get_next_id(&attr, uattr,

					  &map_idr, &map_idr_lock);

		break;

	case BPF_PROG_GET_FD_BY_ID:

		err = bpf_prog_get_fd_by_id(&attr);

		break;

	default:

		err = -EINVAL;

		break;