kbuild speedups, BPF calling conventions, and kernel CVEs

Kernel traffic on 2026-09-12 focused on a large kbuild series claiming major build-time gains, a BPF verifier extension for richer arguments, and several CVE fixes across networking and filesystems. Developers following low-level Linux work will see both performance proposals and stable-security backports.

kbuild series claims faster kernel builds

A 23-patch kbuild series proposes parallelization and Kconfig caching that the author says can speed allmodconfig builds by up to 36 percent. Linus Torvalds and eleven other participants are discussing the patches on linux-kernel. Frequent kernel rebuilders have a clear stake in whether the series lands.

BPF verifier learns by-value structs and __int128

A fifteen-patch bpf-next series teaches the verifier and JITs to accept by-value struct and __int128 arguments for global functions and kfuncs. Four participants reviewed the v3 posting. BPF authors who need wider calling conventions for helpers and kfuncs should track the change.

seg6 decapsulation left stale IP6CB

CVE-2026-80976 fixes a seg6 path that failed to reset IP6CB after IPv6 decapsulation, producing an out-of-bounds read inside ip6_protocol_deliver_rcu. The announcement came through linux-cve-announce. Anyone running SRv6 should pick up the corrected kernel.

nfsd use-after-free in async copy paths

Greg KH announced the backport of a use-after-free fix in nfsd async copy cancel and shutdown under CVE-2026-89675. The race sits in the NFS server shutdown and cancel paths. nfsd operators need the stable update.

page_alloc skips direct compaction for costly NORETRY

A v4 mm/page_alloc patch avoids direct compaction and reclaim for costly __GFP_NORETRY orders, recovering throughput that iomap high-order allocations lost under fragmentation. Seven participants discussed the change on linux-kernel. Workloads that allocate high-order pages under memory pressure are the intended beneficiaries.

BPF bloom filter hardened on 32-bit

CVE-2026-89579 closes bloom-filter allocation overflow and signed-bit indexing bugs that permitted out-of-bounds access on 32-bit kernels. The fix was posted to linux-cve-announce. 32-bit BPF deployments should apply it.

ceph NFS export get_name bounds name length

CVE-2026-89652 bounds the dentry name length copied in ceph NFS-export get_name, blocking an out-of-bounds write from a malicious MDS. The kernel CVE announcement carries the stable fix. Ceph hosts that export via NFS require the update.

MCTP route lookup holds device reference

CVE-2026-80995 makes mctp_route_lookup hold a reference on the route device, closing a local use-after-free reachable by unprivileged AF_MCTP users. The stable announcement documents the change. Systems that use Management Component Transport Protocol should update.