CVE-2024-40958 netns: Make get_net_ns() handle zero refcount net

In the Linux kernel, the following vulnerability has been resolved: netns: Make getnetns handle zero refcount net Syzkaller hit a warning: refcountt: addition on 0; use-after-free. WARNING: CPU: 3 PID: 7890 at lib/refcount.c:25 refcountwarnsaturate+0xdf/0x1d0 Modules linked in: CPU: 3 PID: 7890...