http://thinkiii.blogspot.jp/2014/02/debug-with-slub-allocator.html

The slub allocator in Linux has useful debug features. Such as poisoning, readzone checking, and allocate/free traces with timestamps. It's very useful during product developing stage. Let's create a kernel module and test the debug features.

Make sure slub allocator is built in your kernel.

CONFIG_SLUB_DEBUG=y

CONFIG_SLUB=y

The slub allocator creates additional meta data to store allocate/free traces and timestamps. Everytime slub allocator allocate/free an object, it do poison check (data area) and redzone check  (boundry).

The module shows how it happens. It allocates 32 bytes from kernel and we overwrite the redzone by memset 36 bytes.

void try_to_corrupt_redzone(void)

{

        void *p = kmalloc(32, GFP_KERNEL);

        if (p) {

                pr_alert("p: 0x%p\n", p);

                memset(p, 0x12, 36);    /* write too much */

                print_hex_dump(KERN_ALERT, "mem: ", DUMP_PREFIX_ADDRESS,

                                16, 1, p, 512, 1);

                kfree(p);       /* slub.c should catch this error */

        }

}

static int mymodule_init(void)

{

        pr_alert("%s init\n", __FUNCTION__);

        try_to_corrupt_redzone();

        return 0;

}

static void mymodule_exit(void)

{

        pr_alert("%s exit\n", __FUNCTION__);

}

module_init(mymodule_init);

module_exit(mymodule_exit);

After freeing the object, the kernel checks the object and find that the redzone is overwritten and says:

[ 2050.630002] mymodule_init init

[ 2050.630565] p: 0xddc86680

[ 2050.630653] mem: ddc86680: 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12  ................

[ 2050.630779] mem: ddc86690: 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12  ................

[ 2050.630897] mem: ddc866a0: 12 12 12 12 60 6b c8 dd 16 80 99 e0 fa 8e 2a c1  ....`k........*.

[ 2050.631014] mem: ddc866b0: 16 80 99 e0 ce 92 2a c1 16 80 99 e0 f2 c1 1b c1  ......*.........

[ 2050.631130] mem: ddc866c0: 16 80 99 e0 4c 8b 0a c1 4c 8b 0a c1 61 80 99 e0  ....L...L...a...

[ 2050.631248] mem: ddc866d0: 16 80 99 e0 61 80 99 e0 16 80 99 e0 61 80 99 e0  ....a.......a...

[ 2050.631365] mem: ddc866e0: 75 80 99 e0 48 01 00 c1 2b 36 05 c1 00 00 00 00  u...H...+6......

[ 2050.631483] mem: ddc866f0: 4a 0c 00 00 99 ad 06 00 6d 35 05 c1 9e 8b 2a c1  J.......m5....*.

[ 2050.631599] mem: ddc86700: 6d 35 05 c1 48 8c 2a c1 6d 35 05 c1 ee 89 0a c1  m5..H.*.m5......

[ 2050.631716] mem: ddc86710: ee 89 0a c1 e4 0a 14 c1 e4 0a 14 c1 ee 89 0a c1  ................

[ 2050.631832] mem: ddc86720: ee 89 0a c1 6d 35 05 c1 6d 35 05 c1 6d 35 05 c1  ....m5..m5..m5..

[ 2050.631948] mem: ddc86730: a7 39 05 c1 ef b8 2a c1 00 00 00 00 00 00 00 00  .9....*.........

[ 2050.633948] mem: ddc86740: 4a 0c 00 00 97 ad 06 00 5a 5a 5a 5a 5a 5a 5a 5a  J.......ZZZZZZZZ

[ 2050.634095] mem: ddc86750: 14 dc 46 dd 14 dc 46 dd 00 00 00 00 6b 6b 6b 6b  ..F...F.....kkkk

[ 2050.634236] mem: ddc86760: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b a5  kkkkkkkkkkkkkkk.

[ 2050.634378] mem: ddc86770: cc cc cc cc c0 69 c8 dd a0 83 20 c1 fa 8e 2a c1  .....i.... ...*.

[ 2050.634629] =============================================================================

[ 2050.634750] BUG kmalloc-32 (Tainted: P    B      O): Redzone overwritten

[ 2050.634828] -----------------------------------------------------------------------------

[ 2050.634828]

[ 2050.634967] INFO: 0xddc866a0-0xddc866a3. First byte 0x12 instead of 0xcc

[ 2050.635123] INFO: Allocated in try_to_corrupt_redzone+0x16/0x61 [mymodule] age=1 cpu=0 pid=3146

[ 2050.635255]  alloc_debug_processing+0x63/0xd1

[ 2050.635337]  try_to_corrupt_redzone+0x16/0x61 [mymodule]

[ 2050.635423]  __slab_alloc.constprop.73+0x366/0x384

[ 2050.635506]  try_to_corrupt_redzone+0x16/0x61 [mymodule]

[ 2050.635594]  vt_console_print+0x21e/0x226

[ 2050.635672]  try_to_corrupt_redzone+0x16/0x61 [mymodule]

[ 2050.635758]  kmem_cache_alloc_trace+0x43/0xd7

[ 2050.635832]  kmem_cache_alloc_trace+0x43/0xd7

[ 2050.635909]  mymodule_init+0x0/0x19 [mymodule]

[ 2050.635992]  try_to_corrupt_redzone+0x16/0x61 [mymodule]

[ 2050.636003]  mymodule_init+0x0/0x19 [mymodule]

[ 2050.636092]  try_to_corrupt_redzone+0x16/0x61 [mymodule]

[ 2050.636179]  mymodule_init+0x0/0x19 [mymodule]

[ 2050.636261]  mymodule_init+0x14/0x19 [mymodule]

[ 2050.636343]  do_one_initcall+0x6c/0xf4

[ 2050.636428]  load_module+0x1690/0x199a

[ 2050.636508] INFO: Freed in load_module+0x15d2/0x199a age=3 cpu=0 pid=3146

[ 2050.636598]  free_debug_processing+0xd6/0x142

[ 2050.636676]  load_module+0x15d2/0x199a

[ 2050.636749]  __slab_free+0x3e/0x28d

[ 2050.636819]  load_module+0x15d2/0x199a

[ 2050.636888]  kfree+0xe4/0x102

[ 2050.636953]  kfree+0xe4/0x102

[ 2050.637020]  kobject_uevent_env+0x361/0x39a

[ 2050.637091]  kobject_uevent_env+0x361/0x39a

[ 2050.637163]  kfree+0xe4/0x102

[ 2050.637227]  kfree+0xe4/0x102

[ 2050.637294]  load_module+0x15d2/0x199a

[ 2050.637366]  load_module+0x15d2/0x199a

[ 2050.637438]  load_module+0x15d2/0x199a

[ 2050.637509]  SyS_init_module+0x72/0x8a

[ 2050.637581]  syscall_call+0x7/0xb

[ 2050.637649] INFO: Slab 0xdffa90c0 objects=19 used=8 fp=0xddc86000 flags=0x40000080

[ 2050.637749] INFO: Object 0xddc86680 @offset=1664 fp=0xddc86b60

[ 2050.637749]

[ 2050.637875] Bytes b4 ddc86670: 14 01 00 00 95 ad 06 00 5a 5a 5a 5a 5a 5a 5a 5a  ........ZZZZZZZZ

[ 2050.637875] Object ddc86680: 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12  ................

[ 2050.637875] Object ddc86690: 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12  ................

[ 2050.637875] Redzone ddc866a0: 12 12 12 12                                      ....

[ 2050.637875] Padding ddc86748: 5a 5a 5a 5a 5a 5a 5a 5a                          ZZZZZZZZ

[ 2050.637875] CPU: 0 PID: 3146 Comm: insmod Tainted: P    B      O 3.10.17 #1

[ 2050.637875] Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006

[ 2050.637875]  00000000 c10a7b59 c10941c5 dffa90c0 ddc86680 de8012cc de801280 ddc86680

[ 2050.637875]  dffa90c0 c10a7bd3 c13689a5 ddc866a0 000000cc 00000004 de801280 ddc86680

[ 2050.637875]  dffa90c0 de800e00 c12a8b2f 000000cc ddc86680 de801280 dffa90c0 dd407e50

[ 2050.637875] Call Trace:

[ 2050.637875]  [&ltc10a7b59&gt] ? check_bytes_and_report+0x6d/0xb0

[ 2050.637875]  [&ltc10941c5&gt] ? page_address+0x1a/0x79

[ 2050.637875]  [&ltc10a7bd3&gt] ? check_object+0x37/0x149

[ 2050.637875]  [&ltc12a8b2f&gt] ? free_debug_processing+0x67/0x142

[ 2050.637875]  [&ltc12a8c48&gt] ? __slab_free+0x3e/0x28d

[ 2050.637875]  [&lte0998075&gt] ? mymodule_init+0x14/0x19 [mymodule]

[ 2050.637875]  [&ltc102063d&gt] ? wake_up_klogd+0x1d/0x1e

[ 2050.637875]  [&ltc10a89ee&gt] ? kfree+0xe4/0x102

[ 2050.637875]  [&ltc10a89ee&gt] ? kfree+0xe4/0x102

[ 2050.637875]  [&lte0998075&gt] ? mymodule_init+0x14/0x19 [mymodule]

[ 2050.637875]  [&lte0998075&gt] ? mymodule_init+0x14/0x19 [mymodule]

[ 2050.637875]  [&lte0998061&gt] ? try_to_corrupt_redzone+0x61/0x61 [mymodule]

[ 2050.637875]  [&lte0998075&gt] ? mymodule_init+0x14/0x19 [mymodule]

[ 2050.637875]  [&ltc1000148&gt] ? do_one_initcall+0x6c/0xf4

[ 2050.637875]  [&ltc105362b&gt] ? load_module+0x1690/0x199a

[ 2050.637875]  [&ltc10539a7&gt] ? SyS_init_module+0x72/0x8a

[ 2050.637875]  [&ltc12ab8ef&gt] ? syscall_call+0x7/0xb

[ 2050.637875] FIX kmalloc-32: Restoring 0xddc866a0-0xddc866a3=0xcc

[ 2050.637875]

[ 2051.232817] mymodule_exit exit

First the slub allocator print the error type "redzone overwritten"

[ 2050.634629] =============================================================================

[ 2050.634750] BUG kmalloc-32 (Tainted: P    B      O): Redzone overwritten

[ 2050.634828] -----------------------------------------------------------------------------

[ 2050.634828]

[ 2050.634967] INFO: 0xddc866a0-0xddc866a3. First byte 0x12 instead of 0xcc

To understand what readzone is, take a look at the memory content around the object:

[ 2050.637875] Bytes b4 ddc86670: 14 01 00 00 95 ad 06 00 5a 5a 5a 5a 5a 5a 5a 5a  ........ZZZZZZZZ

[ 2050.637875] Object ddc86680: 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12  ................

[ 2050.637875] Object ddc86690: 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12  ................

[ 2050.637875] Redzone ddc866a0: 12 12 12 12                                      ....

[ 2050.637875] Padding ddc86748: 5a 5a 5a 5a 5a 5a 5a 5a                          ZZZZZZZZ

We fill 38 bytes of 0x12 from the start of the 36-bytes object (0xddc86680 - 0xddc8669f) and 4 more 0x12 on the redzone (normal 0xbb or 0xcc). When the object is returned to the kernel, kernel finds that the redzone is neither 0xcc or 0xbb and reports this as a BUG.

The slub allocator reports the latest allocate/free history of this object. You can see the object is just allocated by our kernel module function 'try_to_corrup_redzone'.

Sometime the traces of the object are more useful than function backtrace. For example, if there exists an use-after-free case:  function A allocates an object and writes if after freeing the object. If the object is allocated by another function B. In this case, function B has a corrupted object, and if we have the free trace of this object, we can trace back to the previous owner of the object, function A.

[ 2050.635123] INFO: Allocated in try_to_corrupt_redzone+0x16/0x61 [mymodule] age=1 cpu=0 pid=3146

[ 2050.635255]  alloc_debug_processing+0x63/0xd1

[ 2050.635337]  try_to_corrupt_redzone+0x16/0x61 [mymodule]

[ 2050.635423]  __slab_alloc.constprop.73+0x366/0x384

[ 2050.635506]  try_to_corrupt_redzone+0x16/0x61 [mymodule]

[ 2050.635594]  vt_console_print+0x21e/0x226

[ 2050.635672]  try_to_corrupt_redzone+0x16/0x61 [mymodule]

[ 2050.635758]  kmem_cache_alloc_trace+0x43/0xd7

[ 2050.635832]  kmem_cache_alloc_trace+0x43/0xd7

[ 2050.635909]  mymodule_init+0x0/0x19 [mymodule]

[ 2050.635992]  try_to_corrupt_redzone+0x16/0x61 [mymodule]

[ 2050.636003]  mymodule_init+0x0/0x19 [mymodule]

[ 2050.636092]  try_to_corrupt_redzone+0x16/0x61 [mymodule]

[ 2050.636179]  mymodule_init+0x0/0x19 [mymodule]

[ 2050.636261]  mymodule_init+0x14/0x19 [mymodule]

[ 2050.636343]  do_one_initcall+0x6c/0xf4

[ 2050.636428]  load_module+0x1690/0x199a

[ 2050.636508] INFO: Freed in load_module+0x15d2/0x199a age=3 cpu=0 pid=3146

[ 2050.636598]  free_debug_processing+0xd6/0x142

[ 2050.636676]  load_module+0x15d2/0x199a

[ 2050.636749]  __slab_free+0x3e/0x28d

[ 2050.636819]  load_module+0x15d2/0x199a

[ 2050.636888]  kfree+0xe4/0x102

[ 2050.636953]  kfree+0xe4/0x102

[ 2050.637020]  kobject_uevent_env+0x361/0x39a

[ 2050.637091]  kobject_uevent_env+0x361/0x39a

[ 2050.637163]  kfree+0xe4/0x102

[ 2050.637227]  kfree+0xe4/0x102

[ 2050.637294]  load_module+0x15d2/0x199a

[ 2050.637366]  load_module+0x15d2/0x199a

[ 2050.637438]  load_module+0x15d2/0x199a

[ 2050.637509]  SyS_init_module+0x72/0x8a
 
Posted by Miles MH Chen at 7:34 AM 
Labels: linux

debug with Linux slub allocator的更多相关文章

  1. (转)Linux SLUB 分配器详解

    原文网址:https://www.ibm.com/developerworks/cn/linux/l-cn-slub/ 多年以来,Linux 内核使用一种称为 SLAB 的内核对象缓冲区分配器.但是, ...

  2. Linux Kernel - Debug Guide (Linux内核调试指南 )

    http://blog.csdn.net/blizmax6/article/details/6747601 linux内核调试指南 一些前言 作者前言 知识从哪里来 为什么撰写本文档 为什么需要汇编级 ...

  3. 【debug】 Linux中top的使用

    在我们日常的开发中,我们经常需要查看每个线程的cpu使用情况.其实,在linux中,top也是我们查看cpu使用状况的一个好帮手 top:先查看每一个进程的使用状况 我们可以发现PID:3800这个经 ...

  4. gdb pretty printer for STL debug in Linux

    Check your gcc version. If it is less than 4.7, you need use another printer.py file. Get the file f ...

  5. [轉]Exploit Linux Kernel Slub Overflow

    Exploit Linux Kernel Slub Overflow By wzt 一.前言 最近几年关于kernel exploit的研究比较热门,常见的内核提权漏洞大致可以分为几类: 空指针引用, ...

  6. 现在的 Linux 内核和 Linux 2.6 的内核有多大区别？

    作者:larmbr宇链接:https://www.zhihu.com/question/35484429/answer/62964898来源:知乎著作权归作者所有.商业转载请联系作者获得授权,非商业转 ...

  7. linux进程用户内存空间和内核空间

    When a process running in user mode requests additional memory, pages are allocated from the list of ...

  8. Linux内存描述之内存页面page--Linux内存管理(四)

    1 Linux如何描述物理内存 Linux把物理内存划分为三个层次来管理 层次 描述 存储节点(Node) CPU被划分为多个节点(node), 内存则被分簇, 每个CPU对应一个本地物理内存, 即一 ...

  9. 转 Linux内存管理原理

    Linux内存管理原理 在用户态,内核态逻辑地址专指下文说的线性偏移前的地址Linux内核虚拟3.伙伴算法和slab分配器 16个页面RAM因为最大连续内存大小为16个页面 页面最多16个页面,所以1 ...

随机推荐

  1. linux备忘录-档案与文件系统的压缩与打包

    知识点 文件扩展名与压缩解压缩工具 .Z -> compress程序压缩的档案 .gz -> gzip程序压缩的档案 .bz2 -> bzip2程序压缩的档案 .tar -> ...

  2. jquery使滚动条滚动到最底部

    $('body').scrollTop($('body')[0].scrollHeight); //想要加载页面自动到最底部要写入function中使用setTimeout function top1 ...

  3. 《c程序设计语言》读书笔记-5.5-指针实现strncpy，strncat，strncmp

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

  4. python类中两个列表实例如何相加或相减

    如下 import numpy a = [1, 2, 3, 4] b = [5, 6, 7, 8] a_array = numpy.array(a) b_array = numpy.array(b) ...

  5. es6+最佳入门实践(4)

    4.函数扩展 4.1.参数默认值 默认参数就是当用户没有传值的时候函数内部默认使用的值,在es5中我们通过逻辑运算符||来实现 function Fn(a, b) { b = b || "n ...

  6. elemetUi 组件--el-checkbox

    [需求]实现选择右边的

  7. HDU 4667 Building Fence(求凸包的周长)

    A - Building Fence Time Limit:1000MS     Memory Limit:65535KB     64bit IO Format:%I64d & %I64u ...

  8. zepto.js 自定义打包集成其他模块构建流程

    1.首先在自己的电脑上要安装Node.js和npm包管理工具: 2.从github上下载zepto.js的源文件包到本地磁盘(例如:E:\Learning\JS): 地址:https://github ...

  9. STL~Deque简介

    转自百度经验deque简介 deque是双向开口的连续性存储空间.虽说是连续性存储空间,但这种连续性只是表面上的,实际上它的内存是动态分配的,它在堆上分配了一块一块的动态储存区,每一块动态存储去本身是 ...

  10. penGL入门学习（六）

    http://blog.csdn.net/sun6255028/article/details/5090067 今天要讲的是动画制作——可能是各位都很喜欢的.除了讲授知识外,我们还会让昨天那个“太阳. ...