mm/hugetlb.c: fix UAF of vma in hugetlb fault pathway

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: mm/hugetlb.c: fix UAF of vma in hugetlb fault pathway Syzbot reports a UAF in hugetlb_fault(). This happens because vmf_anon_prepare() could drop the per-VMA lock and allow the current VMA to be freed before hugetlb_vma_unlock_read() is called. We can fix this by using a modified version of vmf_anon_prepare() that doesn't release the VMA lock on failure, and then release it ourselves after hugetlb_vma_unlock_read().

References

• https://git.kernel.org/stable/c/e897d184a8dd4a4e1f39c8c495598e4d9472776c
• https://git.kernel.org/stable/c/d59ebc99dee0a2687a26df94b901eb8216dbf876
• https://git.kernel.org/stable/c/98b74bb4d7e96b4da5ef3126511febe55b76b807