Linux Kernel CVE-2025-40167

In the Linux kernel, the following vulnerability has been resolved:

ext4: detect invalid INLINE_DATA + EXTENTS flag combination

syzbot reported a BUG_ON in ext4_es_cache_extent() when opening a verity file on a corrupted ext4 filesystem mounted without a journal.

The issue is that the filesystem has an inode with both the INLINE_DATA and EXTENTS flags set:

EXT4-fs error (device loop0): ext4_cache_extents:545: inode #15: comm syz.0.17: corrupted extent tree: lblk 0 < prev 66

Investigation revealed that the inode has both flags set: DEBUG: inode 15 - flag=1, i_inline_off=164, has_inline=1, extents_flag=1

This is an invalid combination since an inode should have either:

• INLINE_DATA: data stored directly in the inode
• EXTENTS: data stored in extent-mapped blocks

Having both flags causes ext4_has_inline_data() to return true, skipping extent tree validation in __ext4_iget(). The unvalidated out-of-order extents then trigger a BUG_ON in ext4_es_cache_extent() due to integer underflow when calculating hole sizes.

Fix this by detecting this invalid flag combination early in ext4_iget() and rejecting the corrupted inode.

The Linux kernel's ext4 filesystem driver is affected across multiple stable branches, as evidenced by the eight git.kernel.org stable-tree fix commits (e.g., 1437c95ab2a2, 1d3ad183943b, de985264eef6, f061f7c331fc). Exact vulnerable-to-fixed version ranges are not enumerated in the provided data, but Ubuntu confirms affected kernels and provides fixed packages via USN-8126-1 (https://ubuntu.com/security/notices/USN-8126-1) and USN-8125-1 (https://ubuntu.com/security/notices/USN-8125-1). No CPE strings were supplied in the input, so precise version boundaries should be confirmed against each distribution's advisory.