CVE-2025-21699 - Addressing the GFS2 Truncate Address Space Flipping Vulnerability in the Linux Kernel

In the Linux kernel development process, security vulnerabilities are discovered and patches are released to correct these issues regularly. Recently, a particular vulnerability has been identified and resolved in the Linux kernel, related to the gfs2 truncate address space flipping. This post will discuss the details of the vulnerability, labeled as CVE-2025-21699, provide the relevant code snippet, and offer links to original sources for further reading.

Vulnerability Details

The vulnerability exists in the GNU/Linux Global File System 2 (GFS2) file system, which is used by the Linux kernel. The issue is related to the flipping of the GFS2_DIF_JDATA flag, and involves the truncation of an inode's address space. When the flag is flipped, the pages in the address space will use either buffer heads or iomap_folio_state structs, but they cannot be mixed together without causing errors.

The vulnerability can be exploited by malicious users or code and might result in unforeseen consequences in the system processing, unexpected crashes, or other security vulnerabilities. Therefore, it was important for the Linux kernel development team to address this issue and release a patch.

Code Snippet

The patch that addresses CVE-2025-21699 involves the following code modification in the fs/gfs2/inode.c file:

-/*
- * Truncate an inode's address space when flipping the GFS2_DIF_JDATA flag:
- * depending on that flag, the pages in the address space will either use
- * iomap_folio structs or buffer heads, and we cannot mix the two.
+ /*
+ * Helper function to truncate the address space depending on the
+ * GFS2_DIF_JDATA flag.
  */
-static void gfs2_truncate_address_space(struct inode *inode)
+void gfs2_truncate_address_space(struct inode *inode)
 {
 	int ret;

 	ret = filemap_fdatawrite(inode->i_mapping);
 	if (ret)
 		pr_warn("%s: i_mapped_write failed (%d), unable to clear mapping for inode %llu\n",
 			__func__, ret, (unsigned long long)GFS2_I(inode)->i_no_addr);
 }

This code snippet truncates the address space depending on the GFS2_DIF_JDATA flag and ensures that the pages in the address space do not mix buffer heads or iomap_folio_state structs.

Original References

For further reading about the Linux kernel, GNU/Linux Global File System 2 (GFS2), and this vulnerability, please refer to the following links:

1. Linux Kernel Source Code: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/?h=v5.17-rc6
2. GFS2 Documentation: https://www.kernel.org/doc/Documentation/filesystems/gfs2.rst
3. CVE (Common Vulnerabilities and Exposures) Database: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2025-21699 (will be available after public publication)

Conclusion

Security vulnerabilities like the GFS2 truncate address space flipping vulnerability are common, and it is essential to stay informed about any fixes and patches for your system. Be sure to keep your Linux kernel up-to-date with the latest security updates.

Timeline

Published on: 02/12/2025 14:15:33 UTC
Last modified on: 03/24/2025 15:38:59 UTC