CVE-2022-50751

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.