UBUNTU-CVE-2026-89678: High severity ubuntu/linux-hwe-edge vulnerability

In the Linux kernel, the following vulnerability has been resolved: nfsd: fix partial-write detection in nfsddirectwrite nfsddirectwrite() walks a list of write segments and, after each vfsiocbiterwrite(), tries to detect a short write so the loop can stop before placing the next segment at a wrong file offset: hosterr = vfsiocbiterwrite(file, kiocb, &segments[i].iter); if (hosterr < 0) return hosterr; cnt += hosterr; if (hosterr < segments[i].iter.count) break; / partial write / vfsiocbiterwrite() runs the iter through ->writeiter(), which advances the iter by the number of bytes written. By the time the check runs, segments[i].iter.count is the residual, not the original request length: before writeiter: iter.count == originallen after writeiter: iter.count == originallen - hosterr The condition then reduces to hosterr < originallen - hosterr, so the break fires only when less than half of the segment was written. Any short write completing between 50% and 99% of the segment slips through; the loop advances to the next segment with kiocb->kipos only bumped by the short amount, writing the next segment's payload at the wrong offset and over-reporting cnt to the NFS client. Snapshot the segment's byte count before the write and compare hosterr against that snapshot so any short write breaks the loop.