利用 Address Sanitizer 工具检查内存访问错误

例子

a.c:
#include <stdio.h>

int main(void) {
        // your code goes here
        int a[3] = {0};
        a[3] = 1;

        printf("%d\n", a[3]);
        return 0;
}

b.c:
#include <stdio.h>
#include <malloc.h>

int main(void) {
        int *p = NULL;

        p = malloc(10 * sizeof(int));
        free(p);
        *p = 3;
        return 0;
}

技巧

gcc从4.8版本起，集成了Address Sanitizer工具，可以用来检查内存访问的错误（编译时指定“-fsanitize=address”）。以上面a.c程序为例：

gcc -fsanitize=address -g -o a a.c

执行a程序：

[root@localhost nan]# ./a
=================================================================
==539==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7fff3a152c9c at pc 0x4009b6 bp 0x7fff3a152c60 sp 0x7fff3a152c58
WRITE of size 4 at 0x7fff3a152c9c thread T0
    #0 0x4009b5 in main /home/nan/a.c:6
    #1 0x34e421ed1c in __libc_start_main (/lib64/libc.so.6+0x34e421ed1c)
    #2 0x4007b8 (/home/nan/a+0x4007b8)

Address 0x7fff3a152c9c is located in stack of thread T0 at offset 44 in frame
    #0 0x400907 in main /home/nan/a.c:3

  This frame has 1 object(s):
    [32, 44) 'a' <== Memory access at offset 44 overflows this variable
HINT: this may be a false positive if your program uses some custom stack unwind mechanism or swapcontext
      (longjmp and C++ exceptions *are* supported)
SUMMARY: AddressSanitizer: stack-buffer-overflow /home/nan/a.c:6 main
Shadow bytes around the buggy address:
  0x100067422540: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x100067422550: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x100067422560: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x100067422570: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x100067422580: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 f1 f1
=>0x100067422590: f1 f1 00[04]f4 f4 f3 f3 f3 f3 00 00 00 00 00 00
  0x1000674225a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x1000674225b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x1000674225c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x1000674225d0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x1000674225e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07
  Heap left redzone:       fa
  Heap right redzone:      fb
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack partial redzone:   f4
  Stack after return:      f5
  Stack use after scope:   f8
  Global redzone:          f9
  Global init order:       f6
  Poisoned by user:        f7
  Contiguous container OOB:fc
  ASan internal:           fe
==539==ABORTING

可以看到，执行程序时检测出了a数组的越界访问（a[3] = 1）。

再看一下b程序：

gcc -fsanitize=address -g -o b b.c

执行b程序：

[root@localhost nan]# ./b
=================================================================
==1951==ERROR: AddressSanitizer: heap-use-after-free on address 0x60400000dfd0 at pc 0x4007f9 bp 0x7fff34277bb0 sp 0x7fff34277ba8
WRITE of size 4 at 0x60400000dfd0 thread T0
    #0 0x4007f8 in main /home/nan/b.c:9
    #1 0x34e421ed1c in __libc_start_main (/lib64/libc.so.6+0x34e421ed1c)
    #2 0x400658 (/home/nan/b+0x400658)

0x60400000dfd0 is located 0 bytes inside of 40-byte region [0x60400000dfd0,0x60400000dff8)
freed by thread T0 here:
    #0 0x7fbbb7a7d057 in __interceptor_free /opt/gcc-4.9.2/src/gcc-4.9.2/libsanitizer/asan/asan_malloc_linux.cc:62
    #1 0x4007c1 in main /home/nan/b.c:8
    #2 0x34e421ed1c in __libc_start_main (/lib64/libc.so.6+0x34e421ed1c)

previously allocated by thread T0 here:
    #0 0x7fbbb7a7d26f in __interceptor_malloc /opt/gcc-4.9.2/src/gcc-4.9.2/libsanitizer/asan/asan_malloc_linux.cc:72
    #1 0x4007b1 in main /home/nan/b.c:7
    #2 0x34e421ed1c in __libc_start_main (/lib64/libc.so.6+0x34e421ed1c)

SUMMARY: AddressSanitizer: heap-use-after-free /home/nan/b.c:9 main
Shadow bytes around the buggy address:
  0x0c087fff9ba0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c087fff9bb0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c087fff9bc0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c087fff9bd0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c087fff9be0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
=>0x0c087fff9bf0: fa fa fa fa fa fa fa fa fa fa[fd]fd fd fd fd fa
  0x0c087fff9c00: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c087fff9c10: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c087fff9c20: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c087fff9c30: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c087fff9c40: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07
  Heap left redzone:       fa
  Heap right redzone:      fb
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack partial redzone:   f4
  Stack after return:      f5
  Stack use after scope:   f8
  Global redzone:          f9
  Global init order:       f6
  Poisoned by user:        f7
  Contiguous container OOB:fc
  ASan internal:           fe
==1951==ABORTING

执行程序时检测出了访问释放内存的错误（*p = 3）。
详情参见 gcc手册