david942j/heapinfo

/*
 @author: david942j
 Getting libc's information, such as:
 - main_arena offset
 - is tcache enabled?
 Sample Usage
 > ./libc_info
 > LD_LIBRARY_PATH=. ./libc_info
 > ./ld-linux.so.2 --library-path . ./libc_info
 */
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define SZ sizeof(size_t)
#define PAGE_SIZE 0x1000

void *search_head(size_t e) {
  e = (e >> 12) << 12;
  while(strncmp((void*)e, "\177ELF", 4)) e -= PAGE_SIZE;
  return (void*) e;
}

void* main_arena_offset() {
  void **p = (void**)malloc(SZ * 128 * 2); // a large chunk
  void *z = malloc(SZ); // prevent p merge with top chunk
  *p = z; // prevent compiler optimize
  free(p); // now *p must be the pointer of the (chunk_ptr) unsorted bin
  z = (void*)((*p) - (4 + 4 + SZ * 10)); // mutex+flags+fastbin[]
  void* a = search_head((size_t)__builtin_return_address(1));
  return (void*)(z - a);
}

int tcache_enable() {
  void **p = malloc(SZ * 32); // smallbin size
  *p = (void*) 0xdeadbeefu;
  // if tcache is enabled, this free will put p into tcache_entry;
  // otherwise, either merge with top_chunk or put into unsorted_bin
  free(p);
  if(*p == 0) return 1; // tcache_entry, fd set as zero
  return 0;
}

int main(int argc, char **argv) {
  printf("{" \
  "\"main_arena_offset\": %u," \
  "\"tcache_enable\": %s" \
  "}\n", main_arena_offset(), tcache_enable() ? "true" : "false");
  return 0;
}