怎么解决 LINUX 堆栈溢出内存的问题

【缓冲区溢出的处理】

你屋子里的门和窗户越少，入侵者进入的方式就越少……

由于缓冲区溢出是一个编程问题，所以只能通过修复被破坏的程序的代码而解决问题。如果你没有源代码，从上面“堆栈溢出攻击”的原理可以看出，要防止此类攻击，我们可以：

① 开放程序时仔细检查溢出情况，不允许数据溢出缓冲区。由于编程和编程语言的原因，这非常困难，而且不适合大量已经在使用的程序；

② 使用检查堆栈溢出的编译器或者在程序中加入某些记号，以便程序运行时确认禁止黑客有意造成的溢出。问题是无法针对已有程序，对新程序来讲，需要修改编译器；

③ 经常检查你的 *** 作系统和应用程序提供商的站点，一旦发现他们提供的补丁程序，就马上下载并且应用在系统上，这是最好的方法。但是系统管理员总要比攻击者慢 一步，如果这个有问题的软件是可选的，甚至是临时的，把它从你的系统中删除。举另外一个例 子，你屋子里的门和窗户越少，入侵者进入的方式就越少。

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char buf[3]

memset(buf,0x55,10)

这个程序就存在溢出

对数据块的访问超出该数据块的地址范围

===================================================================================

【一个检测工具】

Valgrind 是一款 Linux下（支持 x86、x86_64和ppc32）程序的内存调试工具，它可以对编译后的二进制程序进行内存使用监测（C语言中的 malloc 和 free，以及 C++ 中的 new 和 delete），找出内存泄漏问题。

Valgrind 中包含的 Memcheck 工具可以检查以下的程序错误：

使用未初始化的内存 (Use of uninitialised memory)

使用已经释放了的内存 （Reading/writing memory after it has been free’d）

使用超过 malloc 分配的内存空间（Reading/writing off the end of malloc’d blocks）

对堆栈的非法访问（Reading/writing inappropriate areas on the stack）

申请的空间是否有释放（Memory leaks – where pointers to malloc’d blocks are lost forever）

malloc/free/new/delete 申请和释放内存的匹配（Mismatched use of malloc/new/new [] vs free/delete/delete []）

src 和 dst 的重叠（Overlapping src and dst pointers in memcpy() and related functions）

重复 free

① 编译安装 Valgrind：

# wget http://valgrind.org/downloads/valgrind-3.4.1.tar.bz2

# tar xvf valgrind-3.4.1.tar.bz2

# cd valgrind-3.4.1/

# ./configure

…………

Primary build target: X86_LINUX

Secondary build target:

Default supp files: exp-ptrcheck.supp xfree-3.supp xfree-4.supp glibc-2.X-drd.supp glibc-2.34567-NPTL-helgrind.supp glibc-2.5.supp

# make

# make install

# whereis valgrind

valgrind:

/usr/bin/valgrind

/usr/lib/valgrind

/usr/local/bin/valgrind

/usr/local/lib/valgrind

/usr/include/valgrind

/usr/share/man/man1/valgrind.1.gz

运行程序

使用示例：对“ls”程序进程检查，返回结果中的“definitely lost: 0 bytes in 0 blocks.”表示没有内存泄漏。

# /usr/local/bin/valgrind --tool=memcheck --leak-check=full ls /

==29801== Memcheck, a memory error detector.

==29801== Copyright (C) 2002-2008, and GNU GPL'd, by Julian Seward et al.

==29801== Using LibVEX rev 1884, a library for dynamic binary translation.

==29801== Copyright (C) 2004-2008, and GNU GPL'd, by OpenWorks LLP.

==29801== Using valgrind-3.4.1, a dynamic binary instrumentation framework.

==29801== Copyright (C) 2000-2008, and GNU GPL'd, by Julian Seward et al.

==29801== For more details, rerun with: -v

==29801==

bin etc lost+found mnt proc selinuxsys usr

boot home media net root smokeping tftpboot var

dev lib miscopt sbin srvtmp

==29801==

==29801== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 21 from 1)

==29801== malloc/free: in use at exit: 14,744 bytes in 32 blocks.

==29801== malloc/free: 162 allocs, 130 frees, 33,758 bytes allocated.

==29801== For counts of detected errors, rerun with: -v

==29801== searching for pointers to 32 not-freed blocks.

==29801== checked 139,012 bytes.

==29801==

==29801== LEAK SUMMARY:

==29801==definitely lost: 0 bytes in 0 blocks.

==29801== possibly lost: 0 bytes in 0 blocks.

==29801==still reachable: 14,744 bytes in 32 blocks.

==29801== suppressed: 0 bytes in 0 blocks.

==29801== Reachable blocks (those to which a pointer was found) are not shown.

==29801== To see them, rerun with: --leak-check=full --show-reachable=yes

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# /usr/local/bin/valgrind --tool=memcheck --leak-check=full ps /

==29898== Memcheck, a memory error detector.

==29898== Copyright (C) 2002-2008, and GNU GPL'd, by Julian Seward et al.

==29898== Using LibVEX rev 1884, a library for dynamic binary translation.

==29898== Copyright (C) 2004-2008, and GNU GPL'd, by OpenWorks LLP.

==29898== Using valgrind-3.4.1, a dynamic binary instrumentation framework.

==29898== Copyright (C) 2000-2008, and GNU GPL'd, by Julian Seward et al.

==29898== For more details, rerun with: -v

==29898==

ERROR: Garbage option.

********* simple selection ********* ********* selection by list *********

-A all processes -C by command name

-N negate selection -G by real group ID (supports names)

-a all w/ tty except session leaders -U by real user ID (supports names)

-d all except session leaders -g by session OR by effective group name

-e all processes -p by process ID

T all processes on this terminal -s processes in the sessions given

a all w/ tty, including other users -t by tty

g OBSOLETE -- DO NOT USE -u by effective user ID (supports names)

r only running processes U processes for specified users

x processes w/o controlling ttys t by tty

*********** output format ********** *********** long options ***********

-o,o user-defined -f full--Group --User --pid --cols --ppid

-j,j job control s signal --group --user --sid --rows --info

-O,O preloaded -o v virtual memory --cumulative --format --deselect

-l,l long u user-oriented --sort --tty --forest --version

-F extra fullX registers --heading --no-heading --context

********* misc options *********

-V,V show version L list format codes f ASCII art forest

-m,m,-L,-T,H threads S children in sum-y change -l format

-M,Z security data c true command name -c scheduling class

-w,w wide output n numeric WCHAN,UID -H process hierarchy

==29898==

==29898== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 14 from 1)

==29898== malloc/free: in use at exit: 16 bytes in 2 blocks.

==29898== malloc/free: 20 allocs, 18 frees, 2,344 bytes allocated.

==29898== For counts of detected errors, rerun with: -v

==29898== searching for pointers to 2 not-freed blocks.

==29898== checked 263,972 bytes.

==29898==

==29898== 8 bytes in 1 blocks are definitely lost in loss record 2 of 2

==29898==at 0x4005A88: malloc (vg_replace_malloc.c:207)

==29898==by 0xBFF6DF: strdup (in /lib/libc-2.5.so)

==29898==by 0x804A464: (within /bin/ps)

==29898==by 0x804A802: (within /bin/ps)

==29898==by 0x804964D: (within /bin/ps)

==29898==by 0xBA5E8B: (below main) (in /lib/libc-2.5.so)

==29898==

==29898== LEAK SUMMARY:

==29898==definitely lost: 8 bytes in 1 blocks.

==29898== possibly lost: 0 bytes in 0 blocks.

==29898==still reachable: 8 bytes in 1 blocks.

==29898== suppressed: 0 bytes in 0 blocks.

==29898== Reachable blocks (those to which a pointer was found) are not shown.

==29898== To see them, rerun with: --leak-check=full --show-reachable=yes

该类问题一般是由于基础环境配置不当，或硬件配置不能满足当前服务需求导致，如MySQL配置错误，内存不足等。

针对该类问题，排查思路如下：

1. 检查是否为基础服务问题，如对MySQL的最小内存设置进行检查。如果不熟悉数据库调整，可以卸载后重新进行安装恢复默认配置。

2.可以先将mysql停掉，看是否有内存溢出的情况，如果没有那就mysql的问题

3。当前硬件配置较低，如只有512M或1G内存，则可以考虑升级内存后，验证问题是否解决。

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