/*      $OpenBSD: getentropy_osx.c,v 1.14 2021/10/24 21:24:20 deraadt Exp $     */

/*
 * Copyright (c) 2014 Theo de Raadt <deraadt@openbsd.org>
 * Copyright (c) 2014 Bob Beck <beck@obtuse.com>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 *
 * Emulation of getentropy(2) as documented at:
 * http://man.openbsd.org/getentropy.2
 */

#include <TargetConditionals.h>
#include <sys/types.h>
#include <sys/param.h>
#include <sys/ioctl.h>
#include <sys/resource.h>
#include <sys/syscall.h>
#include <sys/sysctl.h>
#include <sys/statvfs.h>
#include <sys/socket.h>
#include <sys/mount.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <stdlib.h>
#include <stdint.h>
#include <stdio.h>
#include <termios.h>
#include <fcntl.h>
#include <signal.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <time.h>
#include <mach/mach_time.h>
#include <mach/mach_host.h>
#include <mach/host_info.h>
#if TARGET_OS_OSX
#include <sys/socketvar.h>
#include <sys/vmmeter.h>
#endif
#include <netinet/in.h>
#include <netinet/tcp.h>
#if TARGET_OS_OSX
#include <netinet/udp.h>
#include <netinet/ip_var.h>
#include <netinet/tcp_var.h>
#include <netinet/udp_var.h>
#endif
#include <CommonCrypto/CommonDigest.h>
#define SHA512_Update(a, b, c)  (CC_SHA512_Update((a), (b), (c)))
#define SHA512_Init(xxx) (CC_SHA512_Init((xxx)))
#define SHA512_Final(xxx, yyy) (CC_SHA512_Final((xxx), (yyy)))
#define SHA512_CTX CC_SHA512_CTX
#define SHA512_DIGEST_LENGTH CC_SHA512_DIGEST_LENGTH

#define REPEAT 5
#define MINIMUM(a, b) (((a) < (b)) ? (a) : (b))

#define HX(a, b) \
        do { \
                if ((a)) \
                        HD(errno); \
                else \
                        HD(b); \
        } while (0)

#define HR(x, l) (SHA512_Update(&ctx, (char *)(x), (l)))
#define HD(x)    (SHA512_Update(&ctx, (char *)&(x), sizeof (x)))
#define HF(x)    (SHA512_Update(&ctx, (char *)&(x), sizeof (void*)))

int     getentropy(void *buf, size_t len);

static int getentropy_urandom(void *buf, size_t len);
static int getentropy_fallback(void *buf, size_t len);

int
getentropy(void *buf, size_t len)
{
        int ret = -1;

        if (len > 256) {
                errno = EIO;
                return (-1);
        }

        /*
         * Try to get entropy with /dev/urandom
         *
         * This can fail if the process is inside a chroot or if file
         * descriptors are exhausted.
         */
        ret = getentropy_urandom(buf, len);
        if (ret != -1)
                return (ret);

        /*
         * Entropy collection via /dev/urandom and sysctl have failed.
         *
         * No other API exists for collecting entropy, and we have
         * no failsafe way to get it on OSX that is not sensitive
         * to resource exhaustion.
         *
         * We have very few options:
         *     - Even syslog_r is unsafe to call at this low level, so
         *       there is no way to alert the user or program.
         *     - Cannot call abort() because some systems have unsafe
         *       corefiles.
         *     - Could raise(SIGKILL) resulting in silent program termination.
         *     - Return EIO, to hint that arc4random's stir function
         *       should raise(SIGKILL)
         *     - Do the best under the circumstances....
         *
         * This code path exists to bring light to the issue that OSX
         * does not provide a failsafe API for entropy collection.
         *
         * We hope this demonstrates that OSX should consider
         * providing a new failsafe API which works in a chroot or
         * when file descriptors are exhausted.
         */
#undef FAIL_INSTEAD_OF_TRYING_FALLBACK
#ifdef FAIL_INSTEAD_OF_TRYING_FALLBACK
        raise(SIGKILL);
#endif
        ret = getentropy_fallback(buf, len);
        if (ret != -1)
                return (ret);

        errno = EIO;
        return (ret);
}

static int
getentropy_urandom(void *buf, size_t len)
{
        struct stat st;
        size_t i;
        int fd, flags;
        int save_errno = errno;

start:

        flags = O_RDONLY;
#ifdef O_NOFOLLOW
        flags |= O_NOFOLLOW;
#endif
#ifdef O_CLOEXEC
        flags |= O_CLOEXEC;
#endif
        fd = open("/dev/urandom", flags);
        if (fd == -1) {
                if (errno == EINTR)
                        goto start;
                goto nodevrandom;
        }
#ifndef O_CLOEXEC
        fcntl(fd, F_SETFD, fcntl(fd, F_GETFD) | FD_CLOEXEC);
#endif

        /* Lightly verify that the device node looks sane */
        if (fstat(fd, &st) == -1 || !S_ISCHR(st.st_mode)) {
                close(fd);
                goto nodevrandom;
        }
        for (i = 0; i < len; ) {
                size_t wanted = len - i;
                ssize_t ret = read(fd, (char *)buf + i, wanted);

                if (ret == -1) {
                        if (errno == EAGAIN || errno == EINTR)
                                continue;
                        close(fd);
                        goto nodevrandom;
                }
                i += ret;
        }
        close(fd);
        errno = save_errno;
        return (0);             /* satisfied */
nodevrandom:
        errno = EIO;
        return (-1);
}

#if TARGET_OS_OSX
static int tcpmib[] = { CTL_NET, AF_INET, IPPROTO_TCP, TCPCTL_STATS };
static int udpmib[] = { CTL_NET, AF_INET, IPPROTO_UDP, UDPCTL_STATS };
static int ipmib[] = { CTL_NET, AF_INET, IPPROTO_IP, IPCTL_STATS };
#endif
static int kmib[] = { CTL_KERN, KERN_USRSTACK };
static int hwmib[] = { CTL_HW, HW_USERMEM };

static int
getentropy_fallback(void *buf, size_t len)
{
        uint8_t results[SHA512_DIGEST_LENGTH];
        int save_errno = errno, e, pgs = getpagesize(), faster = 0, repeat;
        static int cnt;
        struct timespec ts;
        struct timeval tv;
        struct rusage ru;
        sigset_t sigset;
        struct stat st;
        SHA512_CTX ctx;
        static pid_t lastpid;
        pid_t pid;
        size_t i, ii, m;
        char *p;
#if TARGET_OS_OSX
        struct tcpstat tcpstat;
        struct udpstat udpstat;
        struct ipstat ipstat;
#endif
        u_int64_t mach_time;
        unsigned int idata;
        void *addr;

        pid = getpid();
        if (lastpid == pid) {
                faster = 1;
                repeat = 2;
        } else {
                faster = 0;
                lastpid = pid;
                repeat = REPEAT;
        }
        for (i = 0; i < len; ) {
                int j;
                SHA512_Init(&ctx);
                for (j = 0; j < repeat; j++) {
                        HX((e = gettimeofday(&tv, NULL)) == -1, tv);
                        if (e != -1) {
                                cnt += (int)tv.tv_sec;
                                cnt += (int)tv.tv_usec;
                        }

                        mach_time = mach_absolute_time();
                        HD(mach_time);

                        ii = sizeof(addr);
                        HX(sysctl(kmib, sizeof(kmib) / sizeof(kmib[0]),
                            &addr, &ii, NULL, 0) == -1, addr);

                        ii = sizeof(idata);
                        HX(sysctl(hwmib, sizeof(hwmib) / sizeof(hwmib[0]),
                            &idata, &ii, NULL, 0) == -1, idata);

#if TARGET_OS_OSX
                        ii = sizeof(tcpstat);
                        HX(sysctl(tcpmib, sizeof(tcpmib) / sizeof(tcpmib[0]),
                            &tcpstat, &ii, NULL, 0) == -1, tcpstat);

                        ii = sizeof(udpstat);
                        HX(sysctl(udpmib, sizeof(udpmib) / sizeof(udpmib[0]),
                            &udpstat, &ii, NULL, 0) == -1, udpstat);

                        ii = sizeof(ipstat);
                        HX(sysctl(ipmib, sizeof(ipmib) / sizeof(ipmib[0]),
                            &ipstat, &ii, NULL, 0) == -1, ipstat);
#endif

                        HX((pid = getpid()) == -1, pid);
                        HX((pid = getsid(pid)) == -1, pid);
                        HX((pid = getppid()) == -1, pid);
                        HX((pid = getpgid(0)) == -1, pid);
                        HX((e = getpriority(0, 0)) == -1, e);

                        if (!faster) {
                                ts.tv_sec = 0;
                                ts.tv_nsec = 1;
                                (void) nanosleep(&ts, NULL);
                        }

                        HX(sigpending(&sigset) == -1, sigset);
                        HX(sigprocmask(SIG_BLOCK, NULL, &sigset) == -1,
                            sigset);

                        HF(getentropy); /* an addr in this library */
                        HF(printf);             /* an addr in libc */
                        p = (char *)&p;
                        HD(p);          /* an addr on stack */
                        p = (char *)&errno;
                        HD(p);          /* the addr of errno */

                        if (i == 0) {
                                struct sockaddr_storage ss;
                                struct statvfs stvfs;
                                struct termios tios;
                                struct statfs stfs;
                                socklen_t ssl;
                                off_t off;

                                /*
                                 * Prime-sized mappings encourage fragmentation;
                                 * thus exposing some address entropy.
                                 */
                                struct mm {
                                        size_t  npg;
                                        void    *p;
                                } mm[] =         {
                                        { 17, MAP_FAILED }, { 3, MAP_FAILED },
                                        { 11, MAP_FAILED }, { 2, MAP_FAILED },
                                        { 5, MAP_FAILED }, { 3, MAP_FAILED },
                                        { 7, MAP_FAILED }, { 1, MAP_FAILED },
                                        { 57, MAP_FAILED }, { 3, MAP_FAILED },
                                        { 131, MAP_FAILED }, { 1, MAP_FAILED },
                                };

                                for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) {
                                        HX(mm[m].p = mmap(NULL,
                                            mm[m].npg * pgs,
                                            PROT_READ|PROT_WRITE,
                                            MAP_PRIVATE|MAP_ANON, -1,
                                            (off_t)0), mm[m].p);
                                        if (mm[m].p != MAP_FAILED) {
                                                size_t mo;

                                                /* Touch some memory... */
                                                p = mm[m].p;
                                                mo = cnt %
                                                    (mm[m].npg * pgs - 1);
                                                p[mo] = 1;
                                                cnt += (int)((long)(mm[m].p)
                                                    / pgs);
                                        }

                                        /* Check cnts and times... */
                                        mach_time = mach_absolute_time();
                                        HD(mach_time);
                                        cnt += (int)mach_time;

                                        HX((e = getrusage(RUSAGE_SELF,
                                            &ru)) == -1, ru);
                                        if (e != -1) {
                                                cnt += (int)ru.ru_utime.tv_sec;
                                                cnt += (int)ru.ru_utime.tv_usec;
                                        }
                                }

                                for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) {
                                        if (mm[m].p != MAP_FAILED)
                                                munmap(mm[m].p, mm[m].npg * pgs);
                                        mm[m].p = MAP_FAILED;
                                }

                                HX(stat(".", &st) == -1, st);
                                HX(statvfs(".", &stvfs) == -1, stvfs);
                                HX(statfs(".", &stfs) == -1, stfs);

                                HX(stat("/", &st) == -1, st);
                                HX(statvfs("/", &stvfs) == -1, stvfs);
                                HX(statfs("/", &stfs) == -1, stfs);

                                HX((e = fstat(0, &st)) == -1, st);
                                if (e == -1) {
                                        if (S_ISREG(st.st_mode) ||
                                            S_ISFIFO(st.st_mode) ||
                                            S_ISSOCK(st.st_mode)) {
                                                HX(fstatvfs(0, &stvfs) == -1,
                                                    stvfs);
                                                HX(fstatfs(0, &stfs) == -1,
                                                    stfs);
                                                HX((off = lseek(0, (off_t)0,
                                                    SEEK_CUR)) < 0, off);
                                        }
                                        if (S_ISCHR(st.st_mode)) {
                                                HX(tcgetattr(0, &tios) == -1,
                                                    tios);
                                        } else if (S_ISSOCK(st.st_mode)) {
                                                memset(&ss, 0, sizeof ss);
                                                ssl = sizeof(ss);
                                                HX(getpeername(0,
                                                    (void *)&ss, &ssl) == -1,
                                                    ss);
                                        }
                                }

                                HX((e = getrusage(RUSAGE_CHILDREN,
                                    &ru)) == -1, ru);
                                if (e != -1) {
                                        cnt += (int)ru.ru_utime.tv_sec;
                                        cnt += (int)ru.ru_utime.tv_usec;
                                }
                        } else {
                                /* Subsequent hashes absorb previous result */
                                HD(results);
                        }

                        HX((e = gettimeofday(&tv, NULL)) == -1, tv);
                        if (e != -1) {
                                cnt += (int)tv.tv_sec;
                                cnt += (int)tv.tv_usec;
                        }

                        HD(cnt);
                }

                SHA512_Final(results, &ctx);
                memcpy((char *)buf + i, results, MINIMUM(sizeof(results), len - i));
                i += MINIMUM(sizeof(results), len - i);
        }
        explicit_bzero(&ctx, sizeof ctx);
        explicit_bzero(results, sizeof results);
        errno = save_errno;
        return (0);             /* satisfied */
}