[PATCH v2 7/9] ubifs: sysfs: Use kset_create_and_add() for ubifs_kset

[Ian Rogers <irogers@google.com>]

ubifs_kset was a static struct kset using a custom ubifs_ktype that
had no default_groups and no .release callback. With
CONFIG_DEBUG_KOBJECT_RELEASE=y, unloading the ubifs module while delayed
kobject release is pending causes a use-after-free on the static kset.

Replace the static ubifs_kset and empty ubifs_ktype with a dynamically
allocated kset via kset_create_and_add().

Fixes: 203a55f04f66 ("ubifs: Fix memory leak in ubifs_sysfs_init()")
Tested-by: Zhihao Cheng <chengzhihao1@huawei.com>
Reviewed-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: Ian Rogers <irogers@google.com>
---
 fs/ubifs/sysfs.c | 24 +++++++-----------------
 1 file changed, 7 insertions(+), 17 deletions(-)

diff --git a/fs/ubifs/sysfs.c b/fs/ubifs/sysfs.c
index dbf967dcf26e..e20931e3a62f 100644
--- a/fs/ubifs/sysfs.c
+++ b/fs/ubifs/sysfs.c
@@ -80,13 +80,7 @@ static const struct kobj_type ubifs_sb_ktype = {
 	.release	= ubifs_sb_release,
 };
 
-static const struct kobj_type ubifs_ktype = {
-	.sysfs_ops	= &ubifs_attr_ops,
-};
-
-static struct kset ubifs_kset = {
-	.kobj	= {.ktype = &ubifs_ktype},
-};
+static struct kset *ubifs_kset;
 
 int ubifs_sysfs_register(struct ubifs_info *c)
 {
@@ -107,7 +101,7 @@ int ubifs_sysfs_register(struct ubifs_info *c)
 		goto out_free;
 	}
 
-	c->kobj.kset = &ubifs_kset;
+	c->kobj.kset = ubifs_kset;
 	init_completion(&c->kobj_unregister);
 
 	ret = kobject_init_and_add(&c->kobj, &ubifs_sb_ktype, NULL,
@@ -139,18 +133,14 @@ void ubifs_sysfs_unregister(struct ubifs_info *c)
 
 int __init ubifs_sysfs_init(void)
 {
-	int ret;
+	ubifs_kset = kset_create_and_add("ubifs", NULL, fs_kobj);
+	if (!ubifs_kset)
+		return -ENOMEM;
 
-	kobject_set_name(&ubifs_kset.kobj, "ubifs");
-	ubifs_kset.kobj.parent = fs_kobj;
-	ret = kset_register(&ubifs_kset);
-	if (ret)
-		kset_put(&ubifs_kset);
-
-	return ret;
+	return 0;
 }
 
 void ubifs_sysfs_exit(void)
 {
-	kset_unregister(&ubifs_kset);
+	kset_unregister(ubifs_kset);
 }
-- 
2.56.0.313.g2479322e68-goog