CVE-2026-31700 net/packet: fix TOCTOU race on mmap'd vnet_hdr in tpacket_snd()

In the Linux kernel, the following vulnerability has been resolved: net/packet: fix TOCTOU race on mmap'd vnethdr in tpacketsnd In tpacketsnd, when PACKETVNETHDR is enabled, vnethdr points directly into the mmap'd TX ring buffer shared with userspace. The kernel validates the header via...