bpf: Allow getting bpf_map from struct_ops kdata

To allow struct_ops implementors to access the bpf_map during reg() and
unreg(), return bpf_map from bpf_struct_ops_get() instead and let
callers check the error. Additionally, expose bpf_struct_ops_get() and
bpf_struct_ops_put() so that kernel modules can use them.

Signed-off-by: Amery Hung <[email protected]>

Author: ameryhung

include/linux/bpf.h

@@ -1948,7 +1948,7 @@ struct bpf_struct_ops_common_value {
 		__register_bpf_struct_ops(st_ops);			\
 	})
 #define BPF_MODULE_OWNER ((void *)((0xeB9FUL << 2) + POISON_POINTER_DELTA))
-bool bpf_struct_ops_get(const void *kdata);
+struct bpf_map *bpf_struct_ops_get(const void *kdata);
 void bpf_struct_ops_put(const void *kdata);
 int bpf_struct_ops_supported(const struct bpf_struct_ops *st_ops, u32 moff);
 int bpf_struct_ops_map_sys_lookup_elem(struct bpf_map *map, void *key,
@@ -1963,7 +1963,7 @@ void bpf_struct_ops_image_free(void *image);
 static inline bool bpf_try_module_get(const void *data, struct module *owner)
 {
 	if (owner == BPF_MODULE_OWNER)
-		return bpf_struct_ops_get(data);
+		return !IS_ERR(bpf_struct_ops_get(data));
 	else
 		return try_module_get(owner);
 }

kernel/bpf/bpf_struct_ops.c

@@ -1150,7 +1150,7 @@ const struct bpf_map_ops bpf_struct_ops_map_ops = {
 /* "const void *" because some subsystem is
  * passing a const (e.g. const struct tcp_congestion_ops *)
  */
-bool bpf_struct_ops_get(const void *kdata)
+struct bpf_map *bpf_struct_ops_get(const void *kdata)
 {
 	struct bpf_struct_ops_value *kvalue;
 	struct bpf_struct_ops_map *st_map;
@@ -1159,9 +1159,9 @@ bool bpf_struct_ops_get(const void *kdata)
 	kvalue = container_of(kdata, struct bpf_struct_ops_value, data);
 	st_map = container_of(kvalue, struct bpf_struct_ops_map, kvalue);
 
-	map = __bpf_map_inc_not_zero(&st_map->map, false);
-	return !IS_ERR(map);
+	return __bpf_map_inc_not_zero(&st_map->map, false);
 }
+EXPORT_SYMBOL_GPL(bpf_struct_ops_get);
 
 void bpf_struct_ops_put(const void *kdata)
 {
@@ -1173,6 +1173,7 @@ void bpf_struct_ops_put(const void *kdata)
 
 	bpf_map_put(&st_map->map);
 }
+EXPORT_SYMBOL_GPL(bpf_struct_ops_put);
 
 static bool bpf_struct_ops_valid_to_reg(struct bpf_map *map)
 {