CVE-2025-38627

Summary

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

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/74cbeeca4f16823ba58c882e1d8b836c0e39c93d
• https://git.kernel.org/stable/c/5d604d40cd3232b09cb339941ef958e49283ed0a
• https://git.kernel.org/stable/c/cc81768212cdc509e5a986274db7bc24d18cde19
• https://git.kernel.org/stable/c/8fae5b6addd5f6895e03797b56e3c7b9f9cd15c9
• https://git.kernel.org/stable/c/39868685c2a94a70762bc6d77dc81d781d05bff5

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