🛡️ CVE-2024-27022 — kernel

fork: defer linking file vma until vma is fully initialized

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

fork: defer linking file vma until vma is fully initialized

Thorvald reported a WARNING [1]. And the root cause is below race:

CPU 1 CPU 2

fork hugetlbfs_fallocate

dup_mmap hugetlbfs_punch_hole

i_mmap_lock_write(mapping);

vma_interval_tree_insert_after -- Child vma is visible through i_mmap tree.

i_mmap_unlock_write(mapping);

hugetlb_dup_vma_private -- Clear vma_lock outside i_mmap_rwsem!

i_mmap_lock_write(mapping);

hugetlb_vmdelete_list

vma_interval_tree_foreach

hugetlb_vma_trylock_write -- Vma_lock is cleared.

tmp->vm_ops->open -- Alloc new vma_lock outside i_mmap_rwsem!

hugetlb_vma_unlock_write -- Vma_lock is assigned!!!

i_mmap_unlock_write(mapping);

hugetlb_dup_vma_private() and hugetlb_vm_op_open() are called outside

i_mmap_rwsem lock while vma lock can be used in the same time. Fix this

by deferring linking file vma until vma is fully initialized. Those vmas

should be initialized first before they can be used.