mm: hugetlb: fix UAF in hugetlb_handle_userfault

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: mm: hugetlb: fix UAF in hugetlb_handle_userfault The vma_lock and hugetlb_fault_mutex are dropped before handling userfault and reacquire them again after handle_userfault(), but reacquire the vma_lock could lead to UAF[1,2] due to the following race, hugetlb_fault hugetlb_no_page /*unlock vma_lock */ hugetlb_handle_userfault handle_userfault /* unlock mm->mmap_lock*/ vm_mmap_pgoff do_mmap mmap_region munmap_vma_range /* clean old vma */ /* lock vma_lock again <--- UAF */ /* unlock vma_lock */ Since the vma_lock will unlock immediately after hugetlb_handle_userfault(), let's drop the unneeded lock and unlock in hugetlb_handle_userfault() to fix the issue. [1] https://lore.kernel.org/linux-mm/000000000000d5e00a05e834962e@google.com/ [2] https://lore.kernel.org/linux-mm/20220921014457.1668-1-liuzixian4@huawei.com/

References

• https://git.kernel.org/stable/c/45c33966759ea1b4040c08dacda99ef623c0ca29
• https://git.kernel.org/stable/c/0db2efb3bff879566f05341d94c3de00ac95c4cc
• https://git.kernel.org/stable/c/dd691973f67b2800a97db723b1ff6f07fdcf7f5a
• https://git.kernel.org/stable/c/78504bcedb2f1bbfb353b4d233c24d641c4dda33
• https://git.kernel.org/stable/c/958f32ce832ba781ac20e11bb2d12a9352ea28fc