CVE-2024-42233

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

filemap: replace pte_offset_map() with pte_offset_map_nolock()

The vmf->ptl in filemap_fault_recheck_pte_none() is still set from

handle_pte_fault(). But at the same time, we did a pte_unmap(vmf->pte).

After a pte_unmap(vmf->pte) unmap and rcu_read_unlock(), the page table

may be racily changed and vmf->ptl maybe fails to protect the actual page

table. Fix this by replacing pte_offset_map() with

pte_offset_map_nolock().

As David said, the PTL pointer might be stale so if we continue to use

it infilemap_fault_recheck_pte_none(), it might trigger UAF. Also, if

the PTL fails, the issue fixed by commit 58f327f2ce80 ("filemap: avoid

unnecessary major faults in filemap_fault()") might reappear.