结构内的字符串 malloc 溢出

Posted 2023-02-18

【中文标题】结构内的字符串 malloc 溢出

【英文标题】：Malloc of string inside struct overflows

【发布时间】：2021-07-12 22:44:52

【问题描述】：

以下代码是我目前正在进行的项目的示例，用 C 编码。

我首先 malloc 一个结构，然后作为示例 malloc 将第一个内部的字符串。当我尝试将文本从另一个字符串复制到其中并使用printf 函数打印时，当我使用-fsanitize=address 作为编译标志进行编译时，它会溢出。

但我不明白为什么，因为我认为我正在为字符串分配足够的内存，因为我只是使用另一个字符串的strlen 来获取长度，而\0 有一个额外的字符。

# include <stdio.h>
# include <stdlib.h>
# include <string.h>

typedef struct s_word

    int     length;
    char    *str;
                       t_word;

typedef struct s_list

    t_word  *word;
                       t_list;

int main(void)

    int     i;
    char    *line = "this is a test";
    t_list  test;

    i = -1;
    test.word = malloc(sizeof(t_word) * 10);
    test.word[0].str = malloc(sizeof(char) * (strlen(line) + 1));
    while (line[++i])
        test.word[0].str[i] = line[i];
    printf("%s\n", test.word[0].str);
    return (0);

=================================================================
==48531==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x00010940071f at pc 0x00010543ef60 bp 0x00016aee76a0 sp 0x00016aee6e28
READ of size 16 at 0x00010940071f thread T0
    #0 0x10543ef5c in printf_common(void*, char const*, char*)+0x750 (libclang_rt.asan_osx_dynamic.dylib:arm64e+0x1ef5c)
    #1 0x10543f7b8 in wrap_printf+0x78 (libclang_rt.asan_osx_dynamic.dylib:arm64e+0x1f7b8)
    #2 0x104f1bc64 in main+0x3ac (a.out:arm64+0x100003c64)
    #3 0x193291f30 in start+0x0 (libdyld.dylib:arm64e+0x16f30)

0x00010940071f is located 0 bytes to the right of 15-byte region [0x000109400710,0x00010940071f)
allocated by thread T0 here:
    #0 0x10545fa6c in wrap_malloc+0x94 (libclang_rt.asan_osx_dynamic.dylib:arm64e+0x3fa6c)
    #1 0x104f1ba20 in main+0x168 (a.out:arm64+0x100003a20)
    #2 0x193291f30 in start+0x0 (libdyld.dylib:arm64e+0x16f30)

SUMMARY: AddressSanitizer: heap-buffer-overflow (libclang_rt.asan_osx_dynamic.dylib:arm64e+0x1ef5c) in printf_common(void*, char const*, char*)+0x750
Shadow bytes around the buggy address:
  0x0070212a0090: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0070212a00a0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0070212a00b0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0070212a00c0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0070212a00d0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
=>0x0070212a00e0: fa fa 00[07]fa fa 00 06 fa fa 00 00 fa fa 00 fa
  0x0070212a00f0: fa fa 00 00 fa fa fd fd fa fa fa fa fa fa fa fa
  0x0070212a0100: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0070212a0110: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0070212a0120: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0070212a0130: 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
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack after return:      f5
  Stack use after scope:   f8
  Global redzone:          f9
  Global init order:       f6
  Poisoned by user:        f7
  Container overflow:      fc
  Array cookie:            ac
  Intra object redzone:    bb
  ASan internal:           fe
  Left alloca redzone:     ca
  Right alloca redzone:    cb
  Shadow gap:              cc
==48531==ABORTING

【参考方案1】：

当line[++i] 变为零时，循环while (line[++i]) 被中断，因此终止的空字符不会复制到test.word[0].str。复制应该是这样的：

do 
    ++i;
    test.word[0].str[i] = line[i];
 while (line[i]);

另一种选择是简单地使用strcpy()：

strcpy(test.word[0].str, line);

【讨论】：

谢谢！那为我修好了。欣赏它。