CVE-2026-99241: ntfs: take invalidate_lock in ntfs_filemap_page_mkwrite()

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

ntfs: take invalidatelock in ntfsfilemappagemkwrite()

ntfsfilemappagemkwrite() calls iomappagemkwrite() without holding mapping->invalidatelock, so a concurrent truncate or fallocate can be in the middle of invalidating pagecache and rewriting the runlist while the write fault maps blocks and dirties the folio. This races with ntfsattrfallocate(), which merges clusters into the in-memory runlist, drops the runlist lock, and only afterwards zeroes the newly allocated clusters on disk; and with the punch-hole/insert/collapse paths that free clusters after truncating the cache.

Per Documentation/filesystems/locking.rst, ->pagemkwrite() must ensure there are no truncate/invalidate races, "usually mapping->invalidatelock is suitable for proper serialization". xfs takes its mmaplock (= the invalidatelock rwsem) shared in exactly this path.

Take invalidatelock shared around iomappagemkwrite(). The read-only fault path is already covered because filemapfault() itself grabs invalidatelock shared on instantiation/read paths; only pagemkwrite was bypassing it in this driver.