CVE-2026-43472 unshare: fix unshare_fs() handling

In the Linux kernel, the following vulnerability has been resolved: unshare: fix unsharefs handling There's an unpleasant corner case in unshare2, when we have a CLONENEWNS in flags and current-fs hadn't been shared at all; in that case copymntns gets passed current-fs instead of a private copy,...