CVE-2026-31438

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

netfs: Fix kernel BUG in netfs_limit_iter() for ITER_KVEC iterators

When a process crashes and the kernel writes a core dump to a 9P
filesystem, __kernel_write() creates an ITER_KVEC iterator. This
iterator reaches netfs_limit_iter() via netfs_unbuffered_write(), which
only handles ITER_FOLIOQ, ITER_BVEC and ITER_XARRAY iterator types,
hitting the BUG() for any other type.

Fix this by adding netfs_limit_kvec() following the same pattern as
netfs_limit_bvec(), since both kvec and bvec are simple segment arrays
with pointer and length fields. Dispatch it from netfs_limit_iter() when
the iterator type is ITER_KVEC.