Linux Kernel CVE-2026-64157

The netfs subsystem (cpe:2.3:a:linux:linux) is a generic network-filesystem caching library used by filesystems such as AFS, Ceph, and NFS when layered over fscache. A 'streaming write' folio is a page that has been written but not yet read from the server - it is marked dirty but not uptodate, and a companion netfs_folio struct tracks the exact byte range (dirty_offset, dirty_len) of pending data. In netfs_invalidate_folio(), when the caller requests partial invalidation of a folio whose dirty region overlaps at the front (invalidation starts at or before dirty_offset but ends before dirty_offset+dirty_len), the function must advance dirty_offset to the end of the invalidation region (iend). The bug is a single incorrect operand: dirty_offset is set to the start of the invalidation region instead of iend, causing the kernel to believe a narrowed - but wrongly positioned - dirty window still covers already-invalidated bytes. No CWE is formally assigned, but the root cause class is an off-by-one / incorrect offset arithmetic error.