CVE-2025-38627

Summary

f2fs: compress: fix UAF of f2fs_inode_info in f2fs_free_dic

Description

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/c36ab955-c8db-4a8b-a9d0-f07b5f426c3f@kernel.org