X-Git-Url: http://andersk.mit.edu/gitweb/openssh.git/blobdiff_plain/6c08112854ee85c536143dc6b1fa6100ad8cc3e3..2b87da3b1fb7c5ca907cb65aa048fada4ad29803:/entropy.c

diff --git a/entropy.c b/entropy.c
index 2a632502..82bb574d 100644
--- a/entropy.c
+++ b/entropy.c
@@ -9,11 +9,6 @@
  * 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. All advertising materials mentioning features or use of this software
- *    must display the following acknowledgement:
- *      This product includes software developed by Markus Friedl.
- * 4. The name of the author 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 ``AS IS'' AND ANY EXPRESS OR
  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
@@ -29,190 +24,209 @@
 
 #include "includes.h"
 
+#include <openssl/rand.h>
+#include <openssl/sha.h>
+
+/* SunOS 4.4.4 needs this */
+#ifdef HAVE_FLOATINGPOINT_H
+# include <floatingpoint.h>
+#endif /* HAVE_FLOATINGPOINT_H */
+
 #include "ssh.h"
 #include "xmalloc.h"
-
-#ifdef HAVE_OPENSSL
-# include <openssl/rand.h>
-# include <openssl/sha.h>
-#endif
-#ifdef HAVE_SSL
-# include <ssl/rand.h>
-# include <ssl/sha.h>
-#endif
+#include "atomicio.h"
+#include "pathnames.h"
+#include "log.h"
 
 RCSID("$Id$");
 
-#ifdef EGD_SOCKET
 #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(EGD_SOCKET) || defined(RANDOM_POOL)
+
+#ifdef EGD_SOCKET
 /* Collect entropy from EGD */
-void get_random_bytes(unsigned char *buf, int len)
+int get_random_bytes(unsigned char *buf, int len)
 {
-	static int egd_socket = -1;
-	int c;
-	char egd_message[2] = { 0x02, 0x00 };
+	int fd;
+	char msg[2];
 	struct sockaddr_un addr;
 	int addr_len;
 
-	memset(&addr, '\0', sizeof(addr));
-	addr.sun_family = AF_UNIX;
-	
-	/* FIXME: compile time check? */
+	/* Sanity checks */
 	if (sizeof(EGD_SOCKET) > sizeof(addr.sun_path))
 		fatal("Random pool path is too long");
-	
-	strcpy(addr.sun_path, EGD_SOCKET);
-	
-	addr_len = offsetof(struct sockaddr_un, sun_path) + sizeof(EGD_SOCKET);
-	
-	if (egd_socket == -1) {
-		egd_socket = socket(AF_UNIX, SOCK_STREAM, 0);
-		if (egd_socket == -1)
-			fatal("Couldn't create AF_UNIX socket: %s", strerror(errno));
-		if (connect(egd_socket, (struct sockaddr*)&addr, addr_len) == -1)
-			fatal("Couldn't connect to EGD socket \"%s\": %s", addr.sun_path, strerror(errno));
-	}	
-
 	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);
+
+	fd = socket(AF_UNIX, SOCK_STREAM, 0);
+	if (fd == -1) {
+		error("Couldn't create AF_UNIX socket: %s", strerror(errno));
+		return(0);
+	}
+
+	if (connect(fd, (struct sockaddr*)&addr, addr_len) == -1) {
+		error("Couldn't connect to EGD socket \"%s\": %s",
+			addr.sun_path, strerror(errno));
+		close(fd);
+		return(0);
+	}
+
 	/* Send blocking read request to EGD */
-	egd_message[1] = len;
+	msg[0] = 0x02;
+	msg[1] = len;
+
+	if (atomicio(write, fd, msg, sizeof(msg)) != sizeof(msg)) {
+		error("Couldn't write to EGD socket \"%s\": %s",
+			EGD_SOCKET, strerror(errno));
+		close(fd);
+		return(0);
+	}
+
+	if (atomicio(read, fd, buf, len) != len) {
+		error("Couldn't read from EGD socket \"%s\": %s",
+			EGD_SOCKET, strerror(errno));
+		close(fd);
+		return(0);
+	}
 
-	c = atomicio(write, egd_socket, egd_message, sizeof(egd_message));
-	if (c == -1)
-		fatal("Couldn't write to EGD socket \"%s\": %s", EGD_SOCKET, strerror(errno));
+	close(fd);
 
-	c = atomicio(read, egd_socket, buf, len);
-	if (c <= 0)
-		fatal("Couldn't read from EGD socket \"%s\": %s", EGD_SOCKET, strerror(errno));
-	
-	close(EGD_SOCKET);
+	return(1);
 }
 #else /* !EGD_SOCKET */
 #ifdef RANDOM_POOL
 /* Collect entropy from /dev/urandom or pipe */
-void get_random_bytes(unsigned char *buf, int len)
+int get_random_bytes(unsigned char *buf, int len)
 {
-	static int random_pool = -1;
-	int c;
+	int random_pool;
 
+	random_pool = open(RANDOM_POOL, O_RDONLY);
 	if (random_pool == -1) {
-		random_pool = open(RANDOM_POOL, O_RDONLY);
-		if (random_pool == -1)
-			fatal("Couldn't open random pool \"%s\": %s", RANDOM_POOL, strerror(errno));
+		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);
 	}
-	
-	c = atomicio(read, random_pool, buf, len);
-	if (c <= 0)
-		fatal("Couldn't read from random pool \"%s\": %s", RANDOM_POOL, strerror(errno));
+
+	close(random_pool);
+
+	return(1);
 }
 #endif /* RANDOM_POOL */
 #endif /* EGD_SOCKET */
 
-#if !defined(EGD_SOCKET) && !defined(RANDOM_POOL)
-/* 
+/*
+ * 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));
+}
+
+/* No-op */
+void init_rng(void) {}
+
+#else /* defined(EGD_SOCKET) || defined(RANDOM_POOL) */
+
+/*
  * FIXME: proper entropy estimations. All current values are guesses
- * FIXME: Need timeout for slow moving programs
+ * FIXME: (ATL) do estimates at compile time?
  * FIXME: More entropy sources
  */
 
-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(const char *path, const char **args, char *hash);
+/* 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 */
-	const char *path;
+	char *path;
 	/* argv to pass to executable */
-	const char *args[5];
+	char *args[5];
+	/* full command string (debug) */
+	char *cmdstring;
 } entropy_source_t;
 
-entropy_source_t entropy_sources[] = {
-#ifdef PROG_LS
-	{ 0.002, PROG_LS,       { "ls", "-alni", "/var/log", NULL } },
-	{ 0.002, PROG_LS,       { "ls", "-alni", "/var/adm", NULL } },
-	{ 0.002, PROG_LS,       { "ls", "-alni", "/var/mail", NULL } },
-	{ 0.002, PROG_LS,       { "ls", "-alni", "/var/spool/mail", NULL } },
-	{ 0.002, PROG_LS,       { "ls", "-alni", "/proc", NULL } },
-	{ 0.002, PROG_LS,       { "ls", "-alni", "/tmp", NULL } },
-#endif
-#ifdef PROG_NETSTAT
-	{ 0.005, PROG_NETSTAT,  { "netstat","-an", NULL, NULL } },
-	{ 0.010, PROG_NETSTAT,  { "netstat","-in", NULL, NULL } },
-	{ 0.002, PROG_NETSTAT,  { "netstat","-rn", NULL, NULL } },
-	{ 0.002, PROG_NETSTAT,  { "netstat","-s", NULL, NULL } },
-#endif
-#ifdef PROG_ARP
-	{ 0.002, PROG_ARP,      { "arp","-a","-n", NULL } },
-#endif
-#ifdef PROG_IFCONFIG
-	{ 0.002, PROG_IFCONFIG, { "ifconfig", "-a", NULL, NULL } },
-#endif
-#ifdef PROG_PS
-	{ 0.003, PROG_PS,       { "ps", "laxww", NULL, NULL } },
-	{ 0.003, PROG_PS,       { "ps", "-al", NULL, NULL } },
-	{ 0.003, PROG_PS,       { "ps", "-efl", NULL, NULL } },
-#endif
-#ifdef PROG_W
-	{ 0.005, PROG_W,        { "w", NULL, NULL, NULL } },
-#endif
-#ifdef PROG_WHO
-	{ 0.001, PROG_WHO,      { "who","-i", NULL, NULL } },
-#endif
-#ifdef PROG_LAST
-	{ 0.001, PROG_LAST,     { "last", NULL, NULL, NULL } },
-#endif
-#ifdef PROG_LASTLOG
-	{ 0.001, PROG_LASTLOG,  { "lastlog", NULL, NULL, NULL } },
-#endif
-#ifdef PROG_DF
-	{ 0.010, PROG_DF,       { "df", NULL, NULL, NULL } },
-	{ 0.010, PROG_DF,       { "df", "-i", NULL, NULL } },
-#endif
-#ifdef PROG_VMSTAT
-	{ 0.010, PROG_VMSTAT,   { "vmstat", NULL, NULL, NULL } },
-#endif
-#ifdef PROG_UPTIME
-	{ 0.001, PROG_UPTIME,   { "uptime", NULL, NULL, NULL } },
-#endif
-#ifdef PROG_IPCS
-	{ 0.001, PROG_IPCS,     { "-a", NULL, NULL, NULL } },
-#endif
-#ifdef PROG_TAIL
-	{ 0.001, PROG_TAIL,     { "tail", "-200", "/var/log/messages", NULL, NULL } },
-	{ 0.001, PROG_TAIL,     { "tail", "-200", "/var/log/syslog", NULL, NULL } },
-	{ 0.001, PROG_TAIL,     { "tail", "-200", "/var/adm/messages", NULL, NULL } },
-	{ 0.001, PROG_TAIL,     { "tail", "-200", "/var/adm/syslog", NULL, NULL } },
-	{ 0.001, PROG_TAIL,     { "tail", "-200", "/var/log/maillog", NULL, NULL } },
-	{ 0.001, PROG_TAIL,     { "tail", "-200", "/var/adm/maillog", NULL, NULL } },
-#endif
-	{ 0.000, NULL,          { NULL, NULL, NULL, NULL, NULL } },
-};
+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 
+double
 stir_from_system(void)
 {
 	double total_entropy_estimate;
 	long int i;
-	
+
 	total_entropy_estimate = 0;
-	
+
 	i = getpid();
-	RAND_add(&i, sizeof(i), 0.1);
+	RAND_add(&i, sizeof(i), 0.5);
 	total_entropy_estimate += 0.1;
-	
+
 	i = getppid();
-	RAND_add(&i, sizeof(i), 0.1);
+	RAND_add(&i, sizeof(i), 0.5);
 	total_entropy_estimate += 0.1;
 
 	i = getuid();
@@ -221,13 +235,13 @@ stir_from_system(void)
 	RAND_add(&i, sizeof(i), 0.0);
 
 	total_entropy_estimate += stir_gettimeofday(1.0);
-	total_entropy_estimate += stir_clock(0.2);
+	total_entropy_estimate += stir_clock(0.5);
 	total_entropy_estimate += stir_rusage(RUSAGE_SELF, 2.0);
 
 	return(total_entropy_estimate);
 }
 
-double 
+double
 stir_from_programs(void)
 {
 	int i;
@@ -236,48 +250,50 @@ stir_from_programs(void)
 	double total_entropy_estimate;
 	char hash[SHA_DIGEST_LENGTH];
 
-	/*
-	 * Run through list of programs twice to catch differences
-	 */
 	total_entropy_estimate = 0;
-	for(i = 0; i < 2; i++) {
+	for(i = 0; i < NUM_ENTROPY_RUNS; i++) {
 		c = 0;
 		while (entropy_sources[c].path != NULL) {
-			/* Hash output from command */
-			entropy_estimate = hash_output_from_command(entropy_sources[c].path,
-				entropy_sources[c].args, 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 /= 10.0 * (i + 1.0);
-			
-			/* Stir it in */
-			RAND_add(hash, sizeof(hash), entropy_estimate);
-
-/* FIXME: turn this off later */
-#if 1
-			debug("Got %0.2f bytes of entropy from %s", entropy_estimate, 
-				entropy_sources[c].path);
-#endif
 
-			total_entropy_estimate += entropy_estimate;
+			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);
-			
+				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);
 }
 
@@ -285,12 +301,12 @@ 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);
 }
 
@@ -299,10 +315,10 @@ 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);
@@ -314,11 +330,11 @@ stir_rusage(int who, double entropy_estimate)
 {
 #ifdef HAVE_GETRUSAGE
 	struct rusage ru;
-	
-   if (getrusage(who, &ru) == -1)
-		fatal("Couldn't getrusage: %s", strerror(errno));
 
-	RAND_add(&ru, sizeof(ru), 0.1);
+	if (getrusage(who, &ru) == -1)
+		return(0);
+
+	RAND_add(&ru, sizeof(ru), entropy_estimate);
 
 	return(entropy_estimate);
 #else /* _HAVE_GETRUSAGE */
@@ -326,27 +342,46 @@ stir_rusage(int who, double entropy_estimate)
 #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(const char *path, const char **args, char *hash)
+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[2048];
+	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]);
@@ -354,18 +389,17 @@ hash_output_from_command(const char *path, const char **args, char *hash)
 			fatal("Couldn't fork: %s", strerror(errno));
 			/* NOTREACHED */
 		case 0: /* Child */
-			close(0);
-			close(1);
-			close(2);
-			dup2(devnull, 0);
-			dup2(p[1], 1);
-			dup2(p[1], 2);
+			dup2(devnull, STDIN_FILENO);
+			dup2(p[1], STDOUT_FILENO);
+			dup2(p[1], STDERR_FILENO);
 			close(p[0]);
 			close(p[1]);
 			close(devnull);
 
-			execv(path, (char**)args);
-			debug("(child) Couldn't exec '%s': %s", path, strerror(errno));
+			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;
@@ -378,56 +412,415 @@ hash_output_from_command(const char *path, const char **args, char *hash)
 	/* Hash output from child */
 	SHA1_Init(&sha);
 	total_bytes_read = 0;
-	while ((bytes_read = read(p[0], buf, sizeof(buf)))	> 0) {
-		SHA1_Update(&sha, buf, bytes_read);
-		total_bytes_read += bytes_read;
-		RAND_add(&bytes_read, sizeof(&bytes_read), 0.0);
+
+	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", path, 
-			strerror(errno));
-		return(-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 (!WIFEXITED(status) || (WEXITSTATUS(status) != 0))
-		return(0.0);
-	else
+	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);
 }
-#endif /* defined(EGD_SOCKET) || defined(RANDOM_POOL) */
 
-#if defined(EGD_SOCKET) || defined(RANDOM_POOL)
 /*
- * Seed OpenSSL's random number pool from Kernel random number generator
- * or EGD
+ * 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
-seed_rng(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)
 {
-	char buf[32];
-	
-	debug("Seeding random number generator");
-	get_random_bytes(buf, sizeof(buf));
-	RAND_add(buf, sizeof(buf), sizeof(buf));
-	memset(buf, '\0', sizeof(buf));
+	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);
 }
-#else /* defined(EGD_SOCKET) || defined(RANDOM_POOL) */
+
+/*
+ * Write a keyfile at exit
+ */
+void
+prng_seed_cleanup(void *junk)
+{
+	prng_write_seedfile();
+}
+
 /*
- * Conditionally Seed OpenSSL's random number pool syscalls and program output
+ * Conditionally Seed OpenSSL's random number pool from
+ * syscalls and program output
  */
 void
 seed_rng(void)
 {
-	debug("Seeding random number generator.");
-	debug("OpenSSL random status is now %i\n", RAND_status());
-	debug("%i bytes from system calls", (int)stir_from_system());
-	debug("%i bytes from programs", (int)stir_from_programs());
-	debug("OpenSSL random status is now %i\n", RAND_status());
+	void *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 = signal(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");
+
+	signal(SIGCHLD, old_sigchld_handler);
+
+	if (!RAND_status())
+		fatal("Couldn't initialise builtin random number generator -- exiting.");
+}
+
+void init_rng(void)
+{
+	int original_euid;
+
+	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 */
+	if ((original_uid != original_euid) && (seteuid(original_uid) == -1))
+		fatal("Couldn't give up privileges");
+
+	prng_read_seedfile();
+
+	if ((original_uid != original_euid) && (seteuid(original_euid) == -1))
+		fatal("Couldn't restore privileges");
+
+	fatal_add_cleanup(prng_seed_cleanup, NULL);
+	atexit(prng_write_seedfile);
+
+	prng_initialised = 1;
 }
+
 #endif /* defined(EGD_SOCKET) || defined(RANDOM_POOL) */