LTS kernels still lack AF_UNIX slab UAF fix for CVE-2026-80521

A one-line fix for CVE-2026-80521, a slab use-after-free in the Linux AF_UNIX garbage collector, is still missing from four supported long-term stable series even though it already landed in mainline and newer stables.

CVE-2026-80521 is a slab use-after-free reachable by an unprivileged user through SCM_RIGHTS file-descriptor passing and close. When the collector drops an edge and a socket vertex has no remaining outbound references, the vertex is moved onto a free list without being unlinked from a persistent strongly connected component structure, so the next garbage-collection pass can write through memory that has already been freed.

David Ballesteros has asked stable maintainers to carry the fix into the 6.1, 6.6, 6.12, and 6.18 trees. He reports the patch is already present on current 7.1 and 7.2 stables and applies cleanly where the vulnerable collector code is identical.

The bug arrived with the strongly connected component rewrite of the AF_UNIX collector in Linux 6.10. That rewrite was later backported into portions of the 6.1 and 6.6 lines, so those LTS kernels became vulnerable well after their original releases; 6.12 and 6.18 inherited it natively. Older long-term kernels that still run the prior collector remain unaffected. The gap on 6.1 matters in particular because that series still ships in widely deployed distributions.