f2fs: compress: fix UAF of f2fs_inode_info in f2fs_free_dic

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

f2fs: compress: fix UAF of f2fs_inode_info in f2fs_free_dic

The decompress_io_ctx may be released asynchronously after

I/O completion. If this file is deleted immediately after read,

and the kworker of processing post_read_wq has not been executed yet

due to high workloads, It is possible that the inode(f2fs_inode_info)

is evicted and freed before it is used f2fs_free_dic.

The UAF case as below:

Thread A Thread B

- f2fs_decompress_end_io

- f2fs_put_dic

- queue_work

add free_dic work to post_read_wq

- do_unlink

- iput

- evict

- call_rcu

This file is deleted after read.

Thread C kworker to process post_read_wq

- rcu_do_batch

- f2fs_free_inode

- kmem_cache_free

inode is freed by rcu

- process_scheduled_works

- f2fs_late_free_dic

- f2fs_free_dic

- f2fs_release_decomp_mem

read (dic->inode)->i_compress_algorithm

This patch store compress_algorithm and sbi in dic to avoid inode UAF.

In addition, the previous solution is deprecated in [1] may cause system hang.

[1] https://lore.kernel.org/all/[email protected]