/* * Copyright (c) 2000 Damien Miller. 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. * * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 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 "includes.h" #include #include #include /* SunOS 4.4.4 needs this */ #ifdef HAVE_FLOATINGPOINT_H # include #endif /* HAVE_FLOATINGPOINT_H */ #include "ssh.h" #include "misc.h" #include "xmalloc.h" #include "atomicio.h" #include "pathnames.h" #include "log.h" RCSID("$Id: entropy.c,v 1.32 2001/02/26 22:20:58 djm Exp $"); #ifndef offsetof # define offsetof(type, member) ((size_t) &((type *)0)->member) #endif /* Number of times to pass through command list gathering entropy */ #define NUM_ENTROPY_RUNS 1 /* Scale entropy estimates back by this amount on subsequent runs */ #define SCALE_PER_RUN 10.0 /* Minimum number of commands to be considered valid */ #define MIN_ENTROPY_SOURCES 16 #define WHITESPACE " \t\n" #ifndef RUSAGE_SELF # define RUSAGE_SELF 0 #endif #ifndef RUSAGE_CHILDREN # define RUSAGE_CHILDREN 0 #endif #if defined(_POSIX_SAVED_IDS) && !defined(BROKEN_SAVED_UIDS) # define SAVED_IDS_WORK_WITH_SETEUID #endif void check_openssl_version(void) { if (SSLeay() != OPENSSL_VERSION_NUMBER) fatal("OpenSSL version mismatch. Built against %x, you " "have %x", OPENSSL_VERSION_NUMBER, SSLeay()); } #if defined(EGD_SOCKET) || defined(RANDOM_POOL) #ifdef EGD_SOCKET /* Collect entropy from EGD */ int get_random_bytes(unsigned char *buf, int len) { int fd; char msg[2]; struct sockaddr_un addr; int addr_len, rval, errors; mysig_t old_sigpipe; /* Sanity checks */ if (sizeof(EGD_SOCKET) > sizeof(addr.sun_path)) fatal("Random pool path is too long"); if (len > 255) fatal("Too many bytes to read from EGD"); memset(&addr, '\0', sizeof(addr)); addr.sun_family = AF_UNIX; strlcpy(addr.sun_path, EGD_SOCKET, sizeof(addr.sun_path)); addr_len = offsetof(struct sockaddr_un, sun_path) + sizeof(EGD_SOCKET); old_sigpipe = mysignal(SIGPIPE, SIG_IGN); errors = rval = 0; reopen: fd = socket(AF_UNIX, SOCK_STREAM, 0); if (fd == -1) { error("Couldn't create AF_UNIX socket: %s", strerror(errno)); goto done; } if (connect(fd, (struct sockaddr*)&addr, addr_len) == -1) { error("Couldn't connect to EGD socket \"%s\": %s", addr.sun_path, strerror(errno)); goto done; } /* Send blocking read request to EGD */ msg[0] = 0x02; msg[1] = len; if (atomicio(write, fd, msg, sizeof(msg)) != sizeof(msg)) { if (errno == EPIPE && errors < 10) { close(fd); errors++; goto reopen; } error("Couldn't write to EGD socket \"%s\": %s", EGD_SOCKET, strerror(errno)); goto done; } if (atomicio(read, fd, buf, len) != len) { if (errno == EPIPE && errors < 10) { close(fd); errors++; goto reopen; } error("Couldn't read from EGD socket \"%s\": %s", EGD_SOCKET, strerror(errno)); goto done; } rval = 1; done: mysignal(SIGPIPE, old_sigpipe); if (fd != -1) close(fd); return(rval); } #else /* !EGD_SOCKET */ #ifdef RANDOM_POOL /* Collect entropy from /dev/urandom or pipe */ int get_random_bytes(unsigned char *buf, int len) { int random_pool; random_pool = open(RANDOM_POOL, O_RDONLY); if (random_pool == -1) { error("Couldn't open random pool \"%s\": %s", RANDOM_POOL, strerror(errno)); return(0); } if (atomicio(read, random_pool, buf, len) != len) { error("Couldn't read from random pool \"%s\": %s", RANDOM_POOL, strerror(errno)); close(random_pool); return(0); } close(random_pool); return(1); } #endif /* RANDOM_POOL */ #endif /* EGD_SOCKET */ /* * Seed OpenSSL's random number pool from Kernel random number generator * or EGD */ void seed_rng(void) { char buf[32]; debug("Seeding random number generator"); if (!get_random_bytes(buf, sizeof(buf))) { if (!RAND_status()) fatal("Entropy collection failed and entropy exhausted"); } else { RAND_add(buf, sizeof(buf), sizeof(buf)); } memset(buf, '\0', sizeof(buf)); } void init_rng(void) { check_openssl_version(); } #else /* defined(EGD_SOCKET) || defined(RANDOM_POOL) */ /* * FIXME: proper entropy estimations. All current values are guesses * FIXME: (ATL) do estimates at compile time? * FIXME: More entropy sources */ /* slow command timeouts (all in milliseconds) */ /* static int entropy_timeout_default = ENTROPY_TIMEOUT_MSEC; */ static int entropy_timeout_current = ENTROPY_TIMEOUT_MSEC; static int prng_seed_saved = 0; static int prng_initialised = 0; uid_t original_uid; typedef struct { /* Proportion of data that is entropy */ double rate; /* Counter goes positive if this command times out */ unsigned int badness; /* Increases by factor of two each timeout */ unsigned int sticky_badness; /* Path to executable */ char *path; /* argv to pass to executable */ char *args[5]; /* full command string (debug) */ char *cmdstring; } entropy_source_t; double stir_from_system(void); double stir_from_programs(void); double stir_gettimeofday(double entropy_estimate); double stir_clock(double entropy_estimate); double stir_rusage(int who, double entropy_estimate); double hash_output_from_command(entropy_source_t *src, char *hash); /* this is initialised from a file, by prng_read_commands() */ entropy_source_t *entropy_sources = NULL; double stir_from_system(void) { double total_entropy_estimate; long int i; total_entropy_estimate = 0; i = getpid(); RAND_add(&i, sizeof(i), 0.5); total_entropy_estimate += 0.1; i = getppid(); RAND_add(&i, sizeof(i), 0.5); total_entropy_estimate += 0.1; i = getuid(); RAND_add(&i, sizeof(i), 0.0); i = getgid(); RAND_add(&i, sizeof(i), 0.0); total_entropy_estimate += stir_gettimeofday(1.0); total_entropy_estimate += stir_clock(0.5); total_entropy_estimate += stir_rusage(RUSAGE_SELF, 2.0); return(total_entropy_estimate); } double stir_from_programs(void) { int i; int c; double entropy_estimate; double total_entropy_estimate; char hash[SHA_DIGEST_LENGTH]; total_entropy_estimate = 0; for(i = 0; i < NUM_ENTROPY_RUNS; i++) { c = 0; while (entropy_sources[c].path != NULL) { if (!entropy_sources[c].badness) { /* Hash output from command */ entropy_estimate = hash_output_from_command(&entropy_sources[c], hash); /* Scale back entropy estimate according to command's rate */ entropy_estimate *= entropy_sources[c].rate; /* Upper bound of entropy estimate is SHA_DIGEST_LENGTH */ if (entropy_estimate > SHA_DIGEST_LENGTH) entropy_estimate = SHA_DIGEST_LENGTH; /* Scale back estimates for subsequent passes through list */ entropy_estimate /= SCALE_PER_RUN * (i + 1.0); /* Stir it in */ RAND_add(hash, sizeof(hash), entropy_estimate); debug3("Got %0.2f bytes of entropy from '%s'", entropy_estimate, entropy_sources[c].cmdstring); total_entropy_estimate += entropy_estimate; /* Execution times should be a little unpredictable */ total_entropy_estimate += stir_gettimeofday(0.05); total_entropy_estimate += stir_clock(0.05); total_entropy_estimate += stir_rusage(RUSAGE_SELF, 0.1); total_entropy_estimate += stir_rusage(RUSAGE_CHILDREN, 0.1); } else { debug2("Command '%s' disabled (badness %d)", entropy_sources[c].cmdstring, entropy_sources[c].badness); if (entropy_sources[c].badness > 0) entropy_sources[c].badness--; } c++; } } return(total_entropy_estimate); } double stir_gettimeofday(double entropy_estimate) { struct timeval tv; if (gettimeofday(&tv, NULL) == -1) fatal("Couldn't gettimeofday: %s", strerror(errno)); RAND_add(&tv, sizeof(tv), entropy_estimate); return(entropy_estimate); } double stir_clock(double entropy_estimate) { #ifdef HAVE_CLOCK clock_t c; c = clock(); RAND_add(&c, sizeof(c), entropy_estimate); return(entropy_estimate); #else /* _HAVE_CLOCK */ return(0); #endif /* _HAVE_CLOCK */ } double stir_rusage(int who, double entropy_estimate) { #ifdef HAVE_GETRUSAGE struct rusage ru; if (getrusage(who, &ru) == -1) return(0); RAND_add(&ru, sizeof(ru), entropy_estimate); return(entropy_estimate); #else /* _HAVE_GETRUSAGE */ return(0); #endif /* _HAVE_GETRUSAGE */ } static int _get_timeval_msec_difference(struct timeval *t1, struct timeval *t2) { int secdiff, usecdiff; secdiff = t2->tv_sec - t1->tv_sec; usecdiff = (secdiff*1000000) + (t2->tv_usec - t1->tv_usec); return (int)(usecdiff / 1000); } double hash_output_from_command(entropy_source_t *src, char *hash) { static int devnull = -1; int p[2]; fd_set rdset; int cmd_eof = 0, error_abort = 0; struct timeval tv_start, tv_current; int msec_elapsed = 0; pid_t pid; int status; char buf[16384]; int bytes_read; int total_bytes_read; SHA_CTX sha; debug3("Reading output from \'%s\'", src->cmdstring); if (devnull == -1) { devnull = open("/dev/null", O_RDWR); if (devnull == -1) fatal("Couldn't open /dev/null: %s", strerror(errno)); } if (pipe(p) == -1) fatal("Couldn't open pipe: %s", strerror(errno)); (void)gettimeofday(&tv_start, NULL); /* record start time */ switch (pid = fork()) { case -1: /* Error */ close(p[0]); close(p[1]); fatal("Couldn't fork: %s", strerror(errno)); /* NOTREACHED */ case 0: /* Child */ dup2(devnull, STDIN_FILENO); dup2(p[1], STDOUT_FILENO); dup2(p[1], STDERR_FILENO); close(p[0]); close(p[1]); close(devnull); setuid(original_uid); execv(src->path, (char**)(src->args)); debug("(child) Couldn't exec '%s': %s", src->cmdstring, strerror(errno)); _exit(-1); default: /* Parent */ break; } RAND_add(&pid, sizeof(&pid), 0.0); close(p[1]); /* Hash output from child */ SHA1_Init(&sha); total_bytes_read = 0; while (!error_abort && !cmd_eof) { int ret; struct timeval tv; int msec_remaining; (void) gettimeofday(&tv_current, 0); msec_elapsed = _get_timeval_msec_difference(&tv_start, &tv_current); if (msec_elapsed >= entropy_timeout_current) { error_abort=1; continue; } msec_remaining = entropy_timeout_current - msec_elapsed; FD_ZERO(&rdset); FD_SET(p[0], &rdset); tv.tv_sec = msec_remaining / 1000; tv.tv_usec = (msec_remaining % 1000) * 1000; ret = select(p[0]+1, &rdset, NULL, NULL, &tv); RAND_add(&tv, sizeof(tv), 0.0); switch (ret) { case 0: /* timer expired */ error_abort = 1; break; case 1: /* command input */ bytes_read = read(p[0], buf, sizeof(buf)); RAND_add(&bytes_read, sizeof(&bytes_read), 0.0); if (bytes_read == -1) { error_abort = 1; break; } else if (bytes_read) { SHA1_Update(&sha, buf, bytes_read); total_bytes_read += bytes_read; } else { cmd_eof = 1; } break; case -1: default: /* error */ debug("Command '%s': select() failed: %s", src->cmdstring, strerror(errno)); error_abort = 1; break; } } SHA1_Final(hash, &sha); close(p[0]); debug3("Time elapsed: %d msec", msec_elapsed); if (waitpid(pid, &status, 0) == -1) { error("Couldn't wait for child '%s' completion: %s", src->cmdstring, strerror(errno)); return(0.0); } RAND_add(&status, sizeof(&status), 0.0); if (error_abort) { /* closing p[0] on timeout causes the entropy command to * SIGPIPE. Take whatever output we got, and mark this command * as slow */ debug2("Command '%s' timed out", src->cmdstring); src->sticky_badness *= 2; src->badness = src->sticky_badness; return(total_bytes_read); } if (WIFEXITED(status)) { if (WEXITSTATUS(status)==0) { return(total_bytes_read); } else { debug2("Command '%s' exit status was %d", src->cmdstring, WEXITSTATUS(status)); src->badness = src->sticky_badness = 128; return (0.0); } } else if (WIFSIGNALED(status)) { debug2("Command '%s' returned on uncaught signal %d !", src->cmdstring, status); src->badness = src->sticky_badness = 128; return(0.0); } else return(0.0); } /* * prng seedfile functions */ int prng_check_seedfile(char *filename) { struct stat st; /* FIXME raceable: eg replace seed between this stat and subsequent open */ /* Not such a problem because we don't trust the seed file anyway */ if (lstat(filename, &st) == -1) { /* Give up on hard errors */ if (errno != ENOENT) debug("WARNING: Couldn't stat random seed file \"%s\": %s", filename, strerror(errno)); return(0); } /* regular file? */ if (!S_ISREG(st.st_mode)) fatal("PRNG seedfile %.100s is not a regular file", filename); /* mode 0600, owned by root or the current user? */ if (((st.st_mode & 0177) != 0) || !(st.st_uid == original_uid)) { debug("WARNING: PRNG seedfile %.100s must be mode 0600, owned by uid %d", filename, getuid()); return(0); } return(1); } void prng_write_seedfile(void) { int fd; char seed[1024]; char filename[1024]; struct passwd *pw; /* Don't bother if we have already saved a seed */ if (prng_seed_saved) return; setuid(original_uid); prng_seed_saved = 1; pw = getpwuid(original_uid); if (pw == NULL) fatal("Couldn't get password entry for current user (%i): %s", original_uid, strerror(errno)); /* Try to ensure that the parent directory is there */ snprintf(filename, sizeof(filename), "%.512s/%s", pw->pw_dir, _PATH_SSH_USER_DIR); mkdir(filename, 0700); snprintf(filename, sizeof(filename), "%.512s/%s", pw->pw_dir, SSH_PRNG_SEED_FILE); debug("writing PRNG seed to file %.100s", filename); RAND_bytes(seed, sizeof(seed)); /* Don't care if the seed doesn't exist */ prng_check_seedfile(filename); if ((fd = open(filename, O_WRONLY|O_TRUNC|O_CREAT, 0600)) == -1) { debug("WARNING: couldn't access PRNG seedfile %.100s (%.100s)", filename, strerror(errno)); } else { if (atomicio(write, fd, &seed, sizeof(seed)) != sizeof(seed)) fatal("problem writing PRNG seedfile %.100s (%.100s)", filename, strerror(errno)); close(fd); } } void prng_read_seedfile(void) { int fd; char seed[1024]; char filename[1024]; struct passwd *pw; pw = getpwuid(original_uid); if (pw == NULL) fatal("Couldn't get password entry for current user (%i): %s", original_uid, strerror(errno)); snprintf(filename, sizeof(filename), "%.512s/%s", pw->pw_dir, SSH_PRNG_SEED_FILE); debug("loading PRNG seed from file %.100s", filename); if (!prng_check_seedfile(filename)) { verbose("Random seed file not found or not valid, ignoring."); return; } /* open the file and read in the seed */ fd = open(filename, O_RDONLY); if (fd == -1) fatal("could not open PRNG seedfile %.100s (%.100s)", filename, strerror(errno)); if (atomicio(read, fd, &seed, sizeof(seed)) != sizeof(seed)) { verbose("invalid or short read from PRNG seedfile %.100s - ignoring", filename); memset(seed, '\0', sizeof(seed)); } close(fd); /* stir in the seed, with estimated entropy zero */ RAND_add(&seed, sizeof(seed), 0.0); } /* * entropy command initialisation functions */ int prng_read_commands(char *cmdfilename) { FILE *f; char *cp; char line[1024]; char cmd[1024]; char path[256]; int linenum; int num_cmds = 64; int cur_cmd = 0; double est; entropy_source_t *entcmd; f = fopen(cmdfilename, "r"); if (!f) { fatal("couldn't read entropy commands file %.100s: %.100s", cmdfilename, strerror(errno)); } entcmd = (entropy_source_t *)xmalloc(num_cmds * sizeof(entropy_source_t)); memset(entcmd, '\0', num_cmds * sizeof(entropy_source_t)); /* Read in file */ linenum = 0; while (fgets(line, sizeof(line), f)) { int arg; char *argv; linenum++; /* skip leading whitespace, test for blank line or comment */ cp = line + strspn(line, WHITESPACE); if ((*cp == 0) || (*cp == '#')) continue; /* done with this line */ /* First non-whitespace char should be double quote delimiting */ /* commandline */ if (*cp != '"') { error("bad entropy command, %.100s line %d", cmdfilename, linenum); continue; } /* first token, command args (incl. argv[0]) in double quotes */ cp = strtok(cp, "\""); if (cp == NULL) { error("missing or bad command string, %.100s line %d -- ignored", cmdfilename, linenum); continue; } strlcpy(cmd, cp, sizeof(cmd)); /* second token, full command path */ if ((cp = strtok(NULL, WHITESPACE)) == NULL) { error("missing command path, %.100s line %d -- ignored", cmdfilename, linenum); continue; } /* did configure mark this as dead? */ if (strncmp("undef", cp, 5) == 0) continue; strlcpy(path, cp, sizeof(path)); /* third token, entropy rate estimate for this command */ if ((cp = strtok(NULL, WHITESPACE)) == NULL) { error("missing entropy estimate, %.100s line %d -- ignored", cmdfilename, linenum); continue; } est = strtod(cp, &argv); /* end of line */ if ((cp = strtok(NULL, WHITESPACE)) != NULL) { error("garbage at end of line %d in %.100s -- ignored", linenum, cmdfilename); continue; } /* save the command for debug messages */ entcmd[cur_cmd].cmdstring = xstrdup(cmd); /* split the command args */ cp = strtok(cmd, WHITESPACE); arg = 0; argv = NULL; do { char *s = (char*)xmalloc(strlen(cp) + 1); strncpy(s, cp, strlen(cp) + 1); entcmd[cur_cmd].args[arg] = s; arg++; } while ((arg < 5) && (cp = strtok(NULL, WHITESPACE))); if (strtok(NULL, WHITESPACE)) error("ignored extra command elements (max 5), %.100s line %d", cmdfilename, linenum); /* Copy the command path and rate estimate */ entcmd[cur_cmd].path = xstrdup(path); entcmd[cur_cmd].rate = est; /* Initialise other values */ entcmd[cur_cmd].sticky_badness = 1; cur_cmd++; /* If we've filled the array, reallocate it twice the size */ /* Do this now because even if this we're on the last command, we need another slot to mark the last entry */ if (cur_cmd == num_cmds) { num_cmds *= 2; entcmd = xrealloc(entcmd, num_cmds * sizeof(entropy_source_t)); } } /* zero the last entry */ memset(&entcmd[cur_cmd], '\0', sizeof(entropy_source_t)); /* trim to size */ entropy_sources = xrealloc(entcmd, (cur_cmd+1) * sizeof(entropy_source_t)); debug("Loaded %d entropy commands from %.100s", cur_cmd, cmdfilename); return (cur_cmd >= MIN_ENTROPY_SOURCES); } /* * Write a keyfile at exit */ void prng_seed_cleanup(void *junk) { prng_write_seedfile(); } /* * Conditionally Seed OpenSSL's random number pool from * syscalls and program output */ void seed_rng(void) { mysig_t old_sigchld_handler; if (!prng_initialised) fatal("RNG not initialised"); /* Make sure some other sigchld handler doesn't reap our entropy */ /* commands */ old_sigchld_handler = mysignal(SIGCHLD, SIG_DFL); debug("Seeded RNG with %i bytes from programs", (int)stir_from_programs()); debug("Seeded RNG with %i bytes from system calls", (int)stir_from_system()); if (!RAND_status()) fatal("Not enough entropy in RNG"); mysignal(SIGCHLD, old_sigchld_handler); if (!RAND_status()) fatal("Couldn't initialise builtin random number generator -- exiting."); } void init_rng(void) { int original_euid; check_openssl_version(); original_uid = getuid(); original_euid = geteuid(); /* Read in collection commands */ if (!prng_read_commands(SSH_PRNG_COMMAND_FILE)) fatal("PRNG initialisation failed -- exiting."); /* Set ourselves up to save a seed upon exit */ prng_seed_saved = 0; /* Give up privs while reading seed file */ #ifdef SAVED_IDS_WORK_WITH_SETEUID if ((original_uid != original_euid) && (seteuid(original_uid) == -1)) fatal("Couldn't give up privileges"); #else /* SAVED_IDS_WORK_WITH_SETEUID */ /* * Propagate the privileged uid to all of our uids. * Set the effective uid to the given (unprivileged) uid. */ if (original_uid != original_euid && setuid(original_euid) == -1 || seteuid(original_uid) == -1) fatal("Couldn't give up privileges"); #endif /* SAVED_IDS_WORK_WITH_SETEUID */ prng_read_seedfile(); #ifdef SAVED_IDS_WORK_WITH_SETEUID if ((original_uid != original_euid) && (seteuid(original_euid) == -1)) fatal("Couldn't restore privileges"); #else /* SAVED_IDS_WORK_WITH_SETEUID */ /* * We are unable to restore the real uid to its unprivileged value. * Propagate the real uid (usually more privileged) to effective uid * as well. */ if (original_uid != original_euid && seteuid(original_euid) == -1 || setuid(original_uid) == -1) fatal("Couldn't restore privileges"); #endif /* SAVED_IDS_WORK_WITH_SETEUID */ fatal_add_cleanup(prng_seed_cleanup, NULL); atexit(prng_write_seedfile); prng_initialised = 1; } #endif /* defined(EGD_SOCKET) || defined(RANDOM_POOL) */