CVE-2026-97927

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

ufs: create the root dentry after loading cylinder metadata

ufs_fill_super() installed sb->s_root before it loaded the cylinder

group structures for a writable mount:

sb->s_root = d_make_root(inode);

...

if (!sb_rdonly(sb))

if (!ufs_read_cylinder_structures(sb))

goto failed;

When ufs_read_cylinder_structures() failed, the error path freed the

in-core superblock information and set sb->s_fs_info to NULL while

sb->s_root stayed installed. get_tree_bdev() then reached

deactivate_locked_super(), and because s_root was present,

generic_shutdown_super() called sync_filesystem() and the put_super

operation. Both dereference UFS_SB(sb), which is now NULL, so a mount

that fails only while reading the cylinder groups oopses during

teardown. A crafted image whose first cylinder group cannot be read

reaches this path.

Load the cylinder group metadata first and create the root dentry last,

so the superblock is published to the VFS only once it is fully set up.

ufs_setup_cstotal() and ufs_read_cylinder_structures() take only the

super_block and do not use the root inode, so the reordering is safe.