CVE-2026-31398: In the Linux kernel, the following vulnerability has been resolved: mm/rmap: fix incorrect pte restoration for lazyfree

A bug in the Linux kernel's memory management was causing the system to crash when handling lazyfree folios (large memory pages marked for lazy freeing). The problem occurred because when unmapping multiple page table entries (PTEs, the pointers that map virtual memory to physical memory) in a batch, the code incorrectly set all of them as writable even if some should have been read-only, which violated memory safety rules and triggered a crash.