CVE-2026-63817

/// Technical description

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

f2fs: validate compress cache inode only when enabled

F2FS_COMPRESS_INO() uses NM_I(sbi)->max_nid as the synthetic inode

number for the compressed page cache inode. That inode only exists when

the compress_cache mount option is enabled.

When compress_cache is disabled, max_nid is outside the valid inode

range. A corrupted directory entry that points to ino == max_nid should

therefore be rejected by f2fs_check_nid_range(). However, is_meta_ino()

currently treats F2FS_COMPRESS_INO() as a meta inode unconditionally,

so f2fs_iget() bypasses do_read_inode() and its nid range check, and

instantiates a fake internal inode instead.

Gate the compressed cache inode case on COMPRESS_CACHE, matching

f2fs_init_compress_inode(). With compress_cache disabled, ino ==

max_nid now follows the normal inode path and is rejected as an

out-of-range nid.

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References