CVE-2026-72132NFS: Charge unstable writes by request size, not folio size

Official description

In the Linux kernel, the following vulnerability has been resolved: NFS: Charge unstable writes by request size, not folio size nfs_folio_mark_unstable() and nfs_folio_clear_commit() charge and uncharge NR_WRITEBACK/WB_WRITEBACK by folio_nr_pages(folio) once per *request* added to or removed from a commit list. This is correct only when a folio has a single associated request. When pg_test splits a folio into N sub-folio requests (e.g. pNFS flexfiles striping with a stripe unit smaller than the folio size, or plain wsize-limited splitting), each of the N requests independently charges the whole folio's page count, inflating the accounting by a factor of N per folio. With large folios and small stripe units this reaches multiple orders of magnitude: a 2 MiB folio split into 512 4 KiB requests can charge up to 512x its real size, pushing global dirty+writeback accounting past the system's dirty threshold and forcing every buffered writer on the host into the hard-throttle path, including unrelated in-kernel NFS server threads sharing the box. Charge each request only for the pages it actually covers.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/a442c258320b689f13d2205eaeeddf8b0e630288
• https://git.kernel.org/stable/c/1f646e23372f3444dc5f0bcb5404a49d26756add
• https://git.kernel.org/stable/c/0ffc032294a29601b1019dba91aa1a930d90df17
• https://git.kernel.org/stable/c/a192b6c149c6ea10cc88869accb78165eb454456
• https://git.kernel.org/stable/c/27934d02cbeb8a957dd11c985a579e58d30c5270