5.5 - CVE-2021-47638

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

ubifs: rename_whiteout: Fix double free for whiteout_ui->data

'whiteout_ui->data' will be freed twice if space budget fail for rename whiteout operation as following process:

rename_whiteout
dev = kmalloc
whiteout_ui->data = dev
kfree(whiteout_ui->data) // Free first time
iput(whiteout)
ubifs_free_inode
kfree(ui->data) // Double free!

KASAN reports: ================================================================== BUG: KASAN: double-free or invalid-free in ubifs_free_inode+0x4f/0x70 Call Trace:
kfree+0x117/0x490
ubifs_free_inode+0x4f/0x70 [ubifs]
i_callback+0x30/0x60
rcu_do_batch+0x366/0xac0
__do_softirq+0x133/0x57f

Allocated by task 1506:
kmem_cache_alloc_trace+0x3c2/0x7a0
do_rename+0x9b7/0x1150 [ubifs]
ubifs_rename+0x106/0x1f0 [ubifs]
do_syscall_64+0x35/0x80

Freed by task 1506:
kfree+0x117/0x490
do_rename.cold+0x53/0x8a [ubifs]
ubifs_rename+0x106/0x1f0 [ubifs]
do_syscall_64+0x35/0x80

The buggy address belongs to the object at ffff88810238bed8 which belongs to the cache kmalloc-8 of size 8 ==================================================================

Let ubifs_free_inode() free 'whiteout_ui->data'. BTW, delete unused assignment 'whiteout_ui->data_len = 0', process 'ubifs_evict_inode() -> ubifs_jnl_delete_inode() -> ubifs_jnl_write_inode()' doesn't need it (because 'inc_nlink(whiteout)' won't be excuted by 'goto out_release',
and the nlink of whiteout inode is 0).