CVE-2026-63817

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.

References

• https://git.kernel.org/stable/c/0969926d987bbde9a1aa49da317582ba37095805
• https://git.kernel.org/stable/c/13e4b59d3a9413f66f116fa6c4828519b960a5ea
• https://git.kernel.org/stable/c/16161444c30d8dff9428abbae42b72ce4e32a932
• https://git.kernel.org/stable/c/29115b8c9172d34e67ab26cc4f6c209b7a236d7a
• https://git.kernel.org/stable/c/5073c66a96a9c23c0c2533ed4ed06e42f9021208