CVE-2025-38627

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]

Red Hat Enterprise Linux is not affected by this vulnerability as the affected f2fs compression logic is not included in supported Red Hat kernels. Within upstream Linux environments where the Flash-Friendly File System is utilized with compression features, a race condition during delayed asynchronous deallocation could result in a use-after-free state. Triggering this flaw requires local privileges to create, read, and delete files on an active f2fs partition under specific timing conditions, posing no risk to standard Red Hat installations.