bpf: export bpf_map_inc_not_zero

Rename existing bpf_map_inc_not_zero to __bpf_map_inc_not_zero to
indicate that it's caller's responsibility to do proper locking.
Create and export bpf_map_inc_not_zero wrapper that properly
locks map_idr_lock. Will be used in the next commit to
hold a map while cloning a socket.

Cc: Martin KaFai Lau <kafai@fb.com>
Cc: Yonghong Song <yhs@fb.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Acked-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

include/linux/bpf.h

@@ -647,6 +647,8 @@ void bpf_map_free_id(struct bpf_map *map, bool do_idr_lock);
 struct bpf_map *bpf_map_get_with_uref(u32 ufd);
 struct bpf_map *__bpf_map_get(struct fd f);
 struct bpf_map * __must_check bpf_map_inc(struct bpf_map *map, bool uref);
+struct bpf_map * __must_check bpf_map_inc_not_zero(struct bpf_map *map,
+						   bool uref);
 void bpf_map_put_with_uref(struct bpf_map *map);
 void bpf_map_put(struct bpf_map *map);
 int bpf_map_charge_memlock(struct bpf_map *map, u32 pages);

kernel/bpf/syscall.c

@@ -683,8 +683,8 @@ struct bpf_map *bpf_map_get_with_uref(u32 ufd)
 }
 
 /* map_idr_lock should have been held */
-static struct bpf_map *bpf_map_inc_not_zero(struct bpf_map *map,
-					    bool uref)
+static struct bpf_map *__bpf_map_inc_not_zero(struct bpf_map *map,
+					      bool uref)
 {
 	int refold;
 
@@ -704,6 +704,16 @@ static struct bpf_map *bpf_map_inc_not_zero(struct bpf_map *map,
 	return map;
 }
 
+struct bpf_map *bpf_map_inc_not_zero(struct bpf_map *map, bool uref)
+{
+	spin_lock_bh(&map_idr_lock);
+	map = __bpf_map_inc_not_zero(map, uref);
+	spin_unlock_bh(&map_idr_lock);
+
+	return map;
+}
+EXPORT_SYMBOL_GPL(bpf_map_inc_not_zero);
+
 int __weak bpf_stackmap_copy(struct bpf_map *map, void *key, void *value)
 {
 	return -ENOTSUPP;
@@ -2177,7 +2187,7 @@ static int bpf_map_get_fd_by_id(const union bpf_attr *attr)
 	spin_lock_bh(&map_idr_lock);
 	map = idr_find(&map_idr, id);
 	if (map)
-		map = bpf_map_inc_not_zero(map, true);
+		map = __bpf_map_inc_not_zero(map, true);
 	else
 		map = ERR_PTR(-ENOENT);
 	spin_unlock_bh(&map_idr_lock);