configfs: fix possible memory leak in configfs_create_dir()

In the Linux kernel, the following vulnerability has been resolved:

configfs: fix possible memory leak in configfs_create_dir()

kmemleak reported memory leaks in configfs_create_dir():

unreferenced object 0xffff888009f6af00 (size 192):
comm "modprobe", pid 3777, jiffies 4295537735 (age 233.784s)
backtrace:
kmem_cache_alloc (mm/slub.c:3250 mm/slub.c:3256 mm/slub.c:3263 mm/slub.c:3273)
new_fragment (./include/linux/slab.h:600 fs/configfs/dir.c:163)
configfs_register_subsystem (fs/configfs/dir.c:1857)
basic_write (drivers/hwtracing/stm/p_basic.c:14) stm_p_basic
do_one_initcall (init/main.c:1296)
do_init_module (kernel/module/main.c:2455)
...

unreferenced object 0xffff888003ba7180 (size 96):
comm "modprobe", pid 3777, jiffies 4295537735 (age 233.784s)
backtrace:
kmem_cache_alloc (mm/slub.c:3250 mm/slub.c:3256 mm/slub.c:3263 mm/slub.c:3273)
configfs_new_dirent (./include/linux/slab.h:723 fs/configfs/dir.c:194)
configfs_make_dirent (fs/configfs/dir.c:248)
configfs_create_dir (fs/configfs/dir.c:296)
configfs_attach_group.isra.28 (fs/configfs/dir.c:816 fs/configfs/dir.c:852)
configfs_register_subsystem (fs/configfs/dir.c:1881)
basic_write (drivers/hwtracing/stm/p_basic.c:14) stm_p_basic
do_one_initcall (init/main.c:1296)
do_init_module (kernel/module/main.c:2455)
...

This is because the refcount is not correct in configfs_make_dirent().
For normal stage, the refcount is changing as:

configfs_register_subsystem()
configfs_create_dir()
configfs_make_dirent()
configfs_new_dirent() # set s_count = 1
dentry->d_fsdata = configfs_get(sd); # s_count = 2
...
configfs_unregister_subsystem()
configfs_remove_dir()
remove_dir()
configfs_remove_dirent() # s_count = 1
dput() ...
*dentry_unlink_inode()*
configfs_d_iput() # s_count = 0, release

However, if we failed in configfs_create():

configfs_register_subsystem()
configfs_create_dir()
configfs_make_dirent() # s_count = 2
...
configfs_create() # fail
->out_remove:
configfs_remove_dirent(dentry)
configfs_put(sd) # s_count = 1
return PTR_ERR(inode);

There is no inode in the error path, so the configfs_d_iput() is lost
and makes sd and fragment memory leaked.

To fix this, when we failed in configfs_create(), manually call
configfs_put(sd) to keep the refcount correct.