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 <ka...@fb.com>
Acked-by: Alexei Starovoitov <a...@fb.com>
Acked-by: Daniel Borkmann <dan...@iogearbox.net>
---
include/uapi/linux/bpf.h | 8 +++--
kernel/bpf/syscall.c | 91 ++++++++++++++++++++++++++++++++++++++++++------
2 files changed, 87 insertions(+), 12 deletions(-)
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index e5c88f39bdc3..6d4e1cc5bd18 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -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)));
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 68a73d453d70..4f9ee57e7140 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -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);
@@ -926,16 +957,21 @@ 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:
@@ -1097,6 +1133,38 @@ 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 = {};
@@ -1182,6 +1250,9 @@ 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;
--
2.9.3
