C/C 动态检测内存错误利器 - ASan

[导读]来自公众号：大胖聊编程作者：大胖ASan，即AddressSanitizer，是一个适用于c/c程序的动态内存错误检测器，它由一个编译器检测模块（LLVMpass）和一个替换malloc函数的运行时库组成，在性能及检测内存错误方面都优于Valgrind，你值得拥有。一适用平台在L...

来自公众号：大胖聊编程
作者：大胖

ASan，即Address Sanitizer，是一个适用于c/c 程序的动态内存错误检测器，它由一个编译器检测模块（LLVM pass）和一个替换malloc函数的运行时库组成，在性能及检测内存错误方面都优于Valgrind，你值得拥有。
一适用平台在LLVM3.1版之后，ASan就是其的一个组成部分，所以所有适用LLVM的平台，且llvm版本大于3.1的，都可以适用ASan来检查c/c 内存错误。对于gcc，则是4.8版本之后才加入ASan，但是ASan的完整功能则是要gcc版本在4.9.2以上。

二强大功能ASan作为编译器内置功能，支持检测各种内存错误：

缓冲区溢出
① 堆内存溢出
② 栈上内存溢出
③ 全局区缓存溢出
悬空指针（引用）
① 使用释放后的堆上内存
② 使用返回的栈上内存
③ 使用退出作用域的变量
非法释放
① 重复释放
② 无效释放
内存泄漏
初始化顺序导致的问题

ASan和Valgrind对比如下图：

三如何使用

使用ASan时，只需gcc选项加上-fsanitize=address选项；
如果想要在使用asan的时候获取更好的性能，可以加上O1或者更高的编译优化选项；
想要在错误信息中让栈追溯信息更友好，可以加上-fno-omit-frame-pointer选项。
本文针对linux x86-64平台，gcc编译器环境实验。

本文实验环境：

[root@yglocal ~]# lsb_release -aLSB Version: :core-4.1-amd64:core-4.1-noarchDistributor ID: CentOSDescription: CentOS Linux release 8.1.1911 (Core) Release: 8.1.1911Codename: Core[root@yglocal ~]# uname -r4.18.0-147.el8.x86_64[root@yglocal ~]# gcc --versiongcc (GCC) 8.3.1 20190507 (Red Hat 8.3.1-4)Copyright (C) 2018 Free Software Foundation, Inc.This is free software; see the source for copying conditions. There is NOwarranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE
在centos上使用ASan，编译会报如下错误（gcc 4.8.5）：

[root@localhost test]# gcc -g -O2 -fsanitize=address -fno-omit-frame-pointer hello.c /usr/bin/ld: cannot find /usr/lib64/libasan.so.0.0.0collect2: error: ld returned 1 exit status

安装libasan即可：

[root@localhost test]# yum install libasan

注：ubuntu x86-64系统只需gcc版本高于4.8即可；但是在rhel/centos上使用ASan功能，除了gcc版本大于4.8之外，还需要安装libasan。
下面针对内存的几种c/c 常见内存错误，编写例子，看下ASan的检测输出情况：

1
堆缓冲区溢出

测试代码：

[root@yglocal asan_test]# vi heap_ovf_test.c

#include #include #include

int main(){ char *heap_buf = (char*)malloc(32*sizeof(char)); memcpy(heap_buf 30, "overflow", 8); //在heap_buf的第30个字节开始，拷贝8个字符

free(heap_buf);

return 0;}
编译并运行：

[root@yglocal asan_test]# gcc -fsanitize=address -fno-omit-frame-pointer -o heap_ovf_test heap_ovf_test.c [root@yglocal asan_test]# ./heap_ovf_test =================================================================

==40602==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x603000000030 at pc 0x7f3de8f91a1d bp 0x7ffd4b4ebb60 sp 0x7ffd4b4eb308

WRITE of size 8 at 0x603000000030 thread T0 #0 0x7f3de8f91a1c (/lib64/libasan.so.5 0x40a1c) #1 0x400845 in main (/root/asan_test/heap_ovf_test 0x400845) #2 0x7f3de8bb1872 in __libc_start_main (/lib64/libc.so.6 0x23872) #3 0x40075d in _start (/root/asan_test/heap_ovf_test 0x40075d)

0x603000000030 is located 0 bytes to the right of 32-byte region [0x603000000010,0x603000000030)allocated by thread T0 here: #0 0x7f3de9040ba8 in __interceptor_malloc (/lib64/libasan.so.5 0xefba8) #1 0x400827 in main (/root/asan_test/heap_ovf_test 0x400827) #2 0x7f3de8bb1872 in __libc_start_main (/lib64/libc.so.6 0x23872)

SUMMARY: AddressSanitizer: heap-buffer-overflow (/lib64/libasan.so.5 0x40a1c) Shadow bytes around the buggy address: 0x0c067fff7fb0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x0c067fff7fc0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x0c067fff7fd0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x0c067fff7fe0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x0c067fff7ff0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00=>0x0c067fff8000: fa fa 00 00 00 00[fa]fa fa fa fa fa fa fa fa fa 0x0c067fff8010: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa 0x0c067fff8020: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa 0x0c067fff8030: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa 0x0c067fff8040: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa 0x0c067fff8050: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa faShadow 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==40602==ABORTING[root@yglocal asan_test]#
可以看到asan报错：==40602==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x603000000030 at xxxx,下面也列出了发生heap-buffer-overflow时的调用链及heap buffer在哪里申请的。

2
栈缓冲区溢出

测试代码：

[root@yglocal asan_test]# vi stack_ovf_test.c

#include #include

int main(){ char stack_buf[4] = {0}; strcpy(stack_buf, "1234");

return 0;}
编译并运行：

[root@yglocal asan_test]# ./stack_ovf_test =================================================================

==38634==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7ffcf3d8b8d4 at pc 0x7f8714bbaa1d bp 0x7ffcf3d8b8a0 sp 0x7ffcf3d8b048

WRITE of size 5 at 0x7ffcf3d8b8d4 thread T0 #0 0x7f8714bbaa1c (/lib64/libasan.so.5 0x40a1c) #1 0x400949 in main (/root/asan_test/stack_ovf_test 0x400949) #2 0x7f87147da872 in __libc_start_main (/lib64/libc.so.6 0x23872) #3 0x4007cd in _start (/root/asan_test/stack_ovf_test 0x4007cd)

Address 0x7ffcf3d8b8d4 is located in stack of thread T0 at offset 36 in frame #0 0x400895 in main (/root/asan_test/stack_ovf_test 0x400895)

This frame has 1 object(s): [32, 36) 'stack_buf' <== Memory access at offset 36 overflows this variableHINT: 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 (/lib64/libasan.so.5 0x40a1c) Shadow bytes around the buggy address: 0x10001e7a96c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x10001e7a96d0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x10001e7a96e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x10001e7a96f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x10001e7a9700: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00=>0x10001e7a9710: 00 00 00 00 00 00 f1 f1 f1 f1[04]f2 f2 f2 f3 f3 0x10001e7a9720: f3 f3 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x10001e7a9730: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x10001e7a9740: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x10001e7a9750: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x10001e7a9760: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00......

可以看到asan报错：==38634==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7ffcf3d8b8d4 at xxx，发生stack buffer overflow时函数的调用链信息。

3
使用悬空指针

测试代码：

[root@yglocal asan_test]# vi dangling_pointer_test.c

#include #include #include

int main(){ char *p = (char*)malloc(32*sizeof(char)); free(p);

int a = p[1];

return 0;}编译并运行：

[root@yglocal asan_test]# gcc -fsanitize=address -fno-omit-frame-pointer -o dangling_pointer_test dangling_pointer_test.c

[root@yglocal asan_test]# ./dangling_pointer_test =================================================================

==83532==ERROR: AddressSanitizer: heap-use-after-free on address 0x603000000011 at pc 0x0000004007c4 bp 0x7ffd7f562760 sp 0x7ffd7f562750

READ of size 1 at 0x603000000011 thread T0 #0 0x4007c3 in main (/root/asan_test/dangling_pointer_test 0x4007c3) #1 0x7f56196cd872 in __libc_start_main (/lib64/libc.so.6 0x23872) #2 0x4006ad in _start (/root/asan_test/dangling_pointer_test 0x4006ad)

0x603000000011 is located 1 bytes inside of 32-byte region [0x603000000010,0x603000000030)freed by thread T0 here: #0 0x7f5619b5c7e0 in __interceptor_free (/lib64/libasan.so.5 0xef7e0) #1 0x400787 in main (/root/asan_test/dangling_pointer_test 0x400787) #2 0x7f56196cd872 in __libc_start_main (/lib64/libc.so.6 0x23872)

previously allocated by thread T0 here: #0 0x7f5619b5cba8 in __interceptor_malloc (/lib64/libasan.so.5 0xefba8) #1 0x400777 in main (/root/asan_test/dangling_pointer_test 0x400777) #2 0x7f56196cd872 in __libc_start_main (/lib64/libc.so.6 0x23872)

SUMMARY: AddressSanitizer: heap-use-after-free (/root/asan_test/dangling_pointer_test 0x4007c3) in mainShadow bytes around the buggy address: 0x0c067fff7fb0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x0c067fff7fc0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x0c067fff7fd0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x0c067fff7fe0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x0c067fff7ff0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00=>0x0c067fff8000: fa fa[fd]fd fd fd fa fa fa fa fa fa fa fa fa fa 0x0c067fff8010: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa 0x0c067fff8020: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa 0x0c067fff8030: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa 0x0c067fff8040: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa 0x0c067fff8050: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa faShadow byte legend (one shadow byte represents 8 application bytes):......
4
使用栈上返回的变量

[root@yglocal asan_test]# vi use-after-return.c

#include #include #include int *ptr;void get_pointer(){ int local[10]; ptr =


                                
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