linux-cve-announce - CVE-2025-38627: f2fs: compress: fix UAF of f2fs_inode_info in f2fs_free

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Message-ID: <2025082231-CVE-2025-38627-7cb6@gregkh>
Date: Fri, 22 Aug 2025 18:00:36 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-38627: f2fs: compress: fix UAF of f2fs_inode_info in f2fs_free_dic

From: Greg Kroah-Hartman <gregkh@...nel.org>

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

The Linux kernel CVE team has assigned CVE-2025-38627 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 6.0 with commit bff139b49d9f70c1ac5384aac94554846aa834de and fixed in 6.16.1 with commit 8fae5b6addd5f6895e03797b56e3c7b9f9cd15c9
	Issue introduced in 6.0 with commit bff139b49d9f70c1ac5384aac94554846aa834de and fixed in 6.17-rc1 with commit 39868685c2a94a70762bc6d77dc81d781d05bff5

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2025-38627
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	fs/f2fs/compress.c
	fs/f2fs/f2fs.h


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/8fae5b6addd5f6895e03797b56e3c7b9f9cd15c9
	https://git.kernel.org/stable/c/39868685c2a94a70762bc6d77dc81d781d05bff5