[RFC bpf-next v3 05/11] bpf: hold module for bpf_struct_ops_map.

[thinker.li@gmail.com]

From: Kui-Feng Lee <thinker.li@gmail.com>

Ensure a module doesn't go away when a struct_ops object is still alive,
being a struct_ops type that is registered by the module.

Signed-off-by: Kui-Feng Lee <thinker.li@gmail.com>
---
 include/linux/bpf.h         | 1 +
 kernel/bpf/bpf_struct_ops.c | 6 ++++++
 2 files changed, 7 insertions(+)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 0776cb584b3f..faaec20156f1 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1627,6 +1627,7 @@ struct bpf_struct_ops {
 	int (*update)(void *kdata, void *old_kdata);
 	int (*validate)(void *kdata);
 	const struct btf *btf;
+	struct module *owner;
 	const struct btf_type *type;
 	const struct btf_type *value_type;
 	const char *name;
diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
index 7c2ef53687ef..ef8a1edec891 100644
--- a/kernel/bpf/bpf_struct_ops.c
+++ b/kernel/bpf/bpf_struct_ops.c
@@ -632,6 +632,8 @@ static void __bpf_struct_ops_map_free(struct bpf_map *map)
 
 static void bpf_struct_ops_map_free(struct bpf_map *map)
 {
+	struct bpf_struct_ops_map *st_map = (struct bpf_struct_ops_map *)map;
+
 	/* The struct_ops's function may switch to another struct_ops.
 	 *
 	 * For example, bpf_tcp_cc_x->init() may switch to
@@ -649,6 +651,7 @@ static void bpf_struct_ops_map_free(struct bpf_map *map)
 	 */
 	synchronize_rcu_mult(call_rcu, call_rcu_tasks);
 
+	module_put(st_map->st_ops->owner);
 	__bpf_struct_ops_map_free(map);
 }
 
@@ -673,6 +676,9 @@ static struct bpf_map *bpf_struct_ops_map_alloc(union bpf_attr *attr)
 	if (!st_ops)
 		return ERR_PTR(-ENOTSUPP);
 
+	if (!try_module_get(st_ops->owner))
+		return ERR_PTR(-EINVAL);
+
 	vt = st_ops->value_type;
 	if (attr->value_size != vt->size)
 		return ERR_PTR(-EINVAL);
-- 
2.34.1