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bpf: Add BPF_PROG_GET_FD_BY_ID

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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: 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 12:15:49 -07:00 committed by David S. Miller
parent 34ad5580f8
commit b16d9aa4c2
2 changed files with 87 additions and 12 deletions
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8
include/uapi/linux/bpf.h
View File

@ -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 */
__u32 start_id;
struct { /* anonymous struct used by BPF_*_GET_*_ID */
union {
__u32 start_id;
__u32 prog_id;
};
__u32 next_id;
};
} __attribute__((aligned(8)));

91
kernel/bpf/syscall.c
View File

@ -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;
spin_lock_bh(&prog_idr_lock);
if (do_idr_lock)
spin_lock_bh(&prog_idr_lock);
else
__acquire(&prog_idr_lock);
idr_remove(&prog_idr, prog->aux->id);
spin_unlock_bh(&prog_idr_lock);
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;