# extended support for (re-)seeding the OpenSSL PRNG from /dev/random
# bnc#703221, FATE#312172

Index: b/audit-bsm.c
===================================================================
--- a/audit-bsm.c
+++ b/audit-bsm.c
@@ -509,4 +509,10 @@ audit_generate_ephemeral_server_key(cons
 {
 	/* not implemented */
 }
+
+void
+audit_linux_prng_seed(long bytes, const char *rf)
+{
+	/* not implemented */
+}
 #endif /* BSM */
Index: b/audit-linux.c
===================================================================
--- a/audit-linux.c
+++ b/audit-linux.c
@@ -407,4 +407,26 @@ audit_generate_ephemeral_server_key(cons
 	if ((audit_ok < 0) && ((audit_ok != -1) || (getuid() == 0)))
 		error("cannot write into audit");
 }
+
+void
+audit_linux_prng_seed(long bytes, const char *rf)
+{
+	char buf[AUDIT_LOG_SIZE];
+	int audit_fd, audit_ok;
+
+	snprintf(buf, sizeof(buf), "op=prng_seed kind=server bytes=%li source=%s ", bytes, rf);
+	audit_fd = audit_open();
+	if (audit_fd < 0) {
+		if (errno != EINVAL && errno != EPROTONOSUPPORT &&
+					 errno != EAFNOSUPPORT)
+			error("cannot open audit");
+		return;
+	}
+	audit_ok = audit_log_user_message(audit_fd, AUDIT_CRYPTO_PARAM_CHANGE_USER,
+			buf, NULL, 0, NULL, 1);
+	audit_close(audit_fd);
+	/* do not abort if the error is EPERM and sshd is run as non root user */
+	if ((audit_ok < 0) && ((audit_ok != -1) || (getuid() == 0)))
+		error("cannot write into audit");
+}
 #endif /* USE_LINUX_AUDIT */
Index: b/audit.c
===================================================================
--- a/audit.c
+++ b/audit.c
@@ -309,5 +309,11 @@ audit_generate_ephemeral_server_key(cons
 {
 	debug("audit create ephemeral server key euid %d fingerprint %s", geteuid(), fp);
 }
+
+void
+audit_linux_prng_seed(long bytes, const char *rf)
+{
+	debug("audit PRNG seed euid %d bytes %li source %s", geteuid(), bytes, rf);
+}
 # endif  /* !defined CUSTOM_SSH_AUDIT_EVENTS */
 #endif /* SSH_AUDIT_EVENTS */
Index: b/audit.h
===================================================================
--- a/audit.h
+++ b/audit.h
@@ -68,5 +68,6 @@ void	audit_session_key_free(int ctos);
 void	audit_session_key_free_body(int ctos, pid_t, uid_t);
 void	audit_destroy_sensitive_data(const char *, pid_t, uid_t);
 void	audit_generate_ephemeral_server_key(const char *);
+void	audit_linux_prng_seed(long, const char *);
 
 #endif /* _SSH_AUDIT_H */
Index: b/entropy.c
===================================================================
--- a/entropy.c
+++ b/entropy.c
@@ -54,6 +54,7 @@
 #include "pathnames.h"
 #include "log.h"
 #include "buffer.h"
+#include "openbsd-compat/port-linux.h"
 
 /*
  * Portable OpenSSH PRNG seeding:
@@ -229,6 +230,9 @@ seed_rng(void)
 	memset(buf, '\0', sizeof(buf));
 
 #endif /* OPENSSL_PRNG_ONLY */
+
+	linux_seed();
+
 	if (RAND_status() != 1)
 		fatal("PRNG is not seeded");
 }
Index: b/openbsd-compat/Makefile.in
===================================================================
--- a/openbsd-compat/Makefile.in
+++ b/openbsd-compat/Makefile.in
@@ -20,7 +20,7 @@ OPENBSD=base64.o basename.o bcrypt_pbkdf
 
 COMPAT=arc4random.o bsd-asprintf.o bsd-closefrom.o bsd-cray.o bsd-cygwin_util.o bsd-getpeereid.o getrrsetbyname-ldns.o bsd-misc.o bsd-nextstep.o bsd-openpty.o bsd-poll.o bsd-setres_id.o bsd-snprintf.o bsd-statvfs.o bsd-waitpid.o fake-rfc2553.o openssl-compat.o xmmap.o xcrypt.o kludge-fd_set.o
 
-PORTS=port-aix.o port-irix.o port-linux.o port-solaris.o port-tun.o port-uw.o
+PORTS=port-aix.o port-irix.o port-linux.o port-linux-prng.o port-solaris.o port-tun.o port-uw.o
 
 .c.o:
 	$(CC) $(CFLAGS) $(CPPFLAGS) -c $<
Index: b/openbsd-compat/port-linux-prng.c
===================================================================
--- /dev/null
+++ b/openbsd-compat/port-linux-prng.c
@@ -0,0 +1,79 @@
+/*
+ * Copyright (c) 2011 Jan F. Chadima <jchadima@redhat.com>
+ *           (c) 2011 Petr Cerny <pcerny@suse.cz>
+ *
+ * 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.
+ */
+
+/*
+ * Linux-specific portability code - prng support
+ */
+
+#include "includes.h"
+#include "defines.h"
+
+#include <errno.h>
+#include <stdarg.h>
+#include <string.h>
+#include <stdio.h>
+#include <openssl/rand.h>
+
+#include "log.h"
+#include "port-linux.h"
+#include "audit.h"
+
+#define RNG_BYTES_DEFAULT	6L
+#define RNG_ENV_VAR			"SSH_USE_STRONG_RNG"
+
+long rand_bytes = 0;
+char *rand_file = NULL;
+
+static void
+linux_seed_init(void)
+{
+	long elen = 0;
+	char *env = getenv(RNG_ENV_VAR);
+
+	if (env) {
+		errno = 0;
+		elen = strtol(env, NULL, 10);
+		if (errno) {
+			debug("bogus value in the %s environment variable, using default %li\n",
+				RNG_ENV_VAR, RNG_BYTES_DEFAULT);
+		}
+	}
+
+	if (elen)
+		rand_file = "/dev/random";
+	else
+		rand_file = "/dev/urandom";
+
+	rand_bytes = MAX(elen, RNG_BYTES_DEFAULT);
+}
+
+void
+linux_seed(void)
+{
+	long len;
+	if (!rand_file)
+		linux_seed_init();
+
+	errno = 0;
+	len = RAND_load_file(rand_file, rand_bytes);
+	if (len != rand_bytes) {
+		if (errno)
+			fatal ("cannot read from %s, %s", random, strerror(errno));
+		else
+			fatal ("EOF reading %s", random);
+	}
+}
Index: b/openbsd-compat/port-linux.h
===================================================================
--- a/openbsd-compat/port-linux.h
+++ b/openbsd-compat/port-linux.h
@@ -19,6 +19,10 @@
 #ifndef _PORT_LINUX_H
 #define _PORT_LINUX_H
 
+extern long rand_bytes;
+extern char *rand_file;
+void linux_seed(void);
+
 #ifdef WITH_SELINUX
 int ssh_selinux_enabled(void);
 void ssh_selinux_setup_pty(char *, const char *);
Index: b/ssh-add.1
===================================================================
--- a/ssh-add.1
+++ b/ssh-add.1
@@ -171,6 +171,20 @@ to make this work.)
 Identifies the path of a
 .Ux Ns -domain
 socket used to communicate with the agent.
+.It Ev SSH_USE_STRONG_RNG
+The reseeding of the OpenSSL random generator is usually done from
+.Cm /dev/urandom .
+If the 
+.Cm SSH_USE_STRONG_RNG
+environment variable is set to value other than
+.Cm 0
+the OpenSSL random generator is reseeded from
+.Cm /dev/random .
+The number of bytes read is defined by the SSH_USE_STRONG_RNG value. 
+Minimum is 6 bytes.
+This setting is not recommended on the computers without the hardware
+random generator because insufficient entropy causes the connection to 
+be blocked until enough entropy is available.
 .El
 .Sh FILES
 .Bl -tag -width Ds
Index: b/ssh-agent.1
===================================================================
--- a/ssh-agent.1
+++ b/ssh-agent.1
@@ -194,6 +194,23 @@ sockets used to contain the connection t
 These sockets should only be readable by the owner.
 The sockets should get automatically removed when the agent exits.
 .El
+.Sh ENVIRONMENT
+.Bl -tag -width Ds -compact
+.Pp
+.It Pa SSH_USE_STRONG_RNG
+The reseeding of the OpenSSL random generator is usually done from
+.Cm /dev/urandom .
+If the 
+.Cm SSH_USE_STRONG_RNG
+environment variable is set to value other than
+.Cm 0
+the OpenSSL random generator is reseeded from
+.Cm /dev/random .
+The number of bytes read is defined by the SSH_USE_STRONG_RNG value. 
+Minimum is 6 bytes.
+This setting is not recommended on the computers without the hardware
+random generator because insufficient entropy causes the connection to 
+be blocked until enough entropy is available.
 .Sh SEE ALSO
 .Xr ssh 1 ,
 .Xr ssh-add 1 ,
Index: b/ssh-keygen.1
===================================================================
--- a/ssh-keygen.1
+++ b/ssh-keygen.1
@@ -842,6 +842,23 @@ Contains Diffie-Hellman groups used for
 The file format is described in
 .Xr moduli 5 .
 .El
+.Sh ENVIRONMENT
+.Bl -tag -width Ds -compact
+.Pp
+.It Pa SSH_USE_STRONG_RNG
+The reseeding of the OpenSSL random generator is usually done from
+.Cm /dev/urandom .
+If the 
+.Cm SSH_USE_STRONG_RNG
+environment variable is set to value other than
+.Cm 0
+the OpenSSL random generator is reseeded from
+.Cm /dev/random .
+The number of bytes read is defined by the SSH_USE_STRONG_RNG value. 
+Minimum is 6 bytes.
+This setting is not recommended on the computers without the hardware
+random generator because insufficient entropy causes the connection to 
+be blocked until enough entropy is available.
 .Sh SEE ALSO
 .Xr ssh 1 ,
 .Xr ssh-add 1 ,
Index: b/ssh-keysign.8
===================================================================
--- a/ssh-keysign.8
+++ b/ssh-keysign.8
@@ -80,6 +80,23 @@ must be set-uid root if host-based authe
 If these files exist they are assumed to contain public certificate
 information corresponding with the private keys above.
 .El
+.Sh ENVIRONMENT
+.Bl -tag -width Ds -compact
+.Pp
+.It Pa SSH_USE_STRONG_RNG
+The reseeding of the OpenSSL random generator is usually done from
+.Cm /dev/urandom .
+If the 
+.Cm SSH_USE_STRONG_RNG
+environment variable is set to value other than
+.Cm 0
+the OpenSSL random generator is reseeded from
+.Cm /dev/random .
+The number of bytes read is defined by the SSH_USE_STRONG_RNG value. 
+Minimum is 6 bytes.
+This setting is not recommended on the computers without the hardware
+random generator because insufficient entropy causes the connection to 
+be blocked until enough entropy is available.
 .Sh SEE ALSO
 .Xr ssh 1 ,
 .Xr ssh-keygen 1 ,
Index: b/ssh.1
===================================================================
--- a/ssh.1
+++ b/ssh.1
@@ -1415,6 +1415,20 @@ For more information, see the
 .Cm PermitUserEnvironment
 option in
 .Xr sshd_config 5 .
+.It Ev SSH_USE_STRONG_RNG
+The reseeding of the OpenSSL random generator is usually done from
+.Cm /dev/urandom .
+If the 
+.Cm SSH_USE_STRONG_RNG
+environment variable is set to value other than
+.Cm 0
+the OpenSSL random generator is reseeded from
+.Cm /dev/random .
+The number of bytes read is defined by the SSH_USE_STRONG_RNG value. 
+Minimum is 6 bytes.
+This setting is not recommended on the computers without the hardware
+random generator because insufficient entropy causes the connection to 
+be blocked until enough entropy is available.
 .Sh FILES
 .Bl -tag -width Ds -compact
 .It Pa ~/.rhosts
Index: b/sshd.8
===================================================================
--- a/sshd.8
+++ b/sshd.8
@@ -944,6 +944,23 @@ concurrently for different ports, this c
 started last).
 The content of this file is not sensitive; it can be world-readable.
 .El
+.Sh ENVIRONMENT
+.Bl -tag -width Ds -compact
+.Pp
+.It Pa SSH_USE_STRONG_RNG
+The reseeding of the OpenSSL random generator is usually done from
+.Cm /dev/urandom .
+If the 
+.Cm SSH_USE_STRONG_RNG
+environment variable is set to value other than
+.Cm 0
+the OpenSSL random generator is reseeded from
+.Cm /dev/random .
+The number of bytes read is defined by the SSH_USE_STRONG_RNG value. 
+Minimum is 6 bytes.
+This setting is not recommended on the computers without the hardware
+random generator because insufficient entropy causes the connection to 
+be blocked until enough entropy is available.
 .Sh SEE ALSO
 .Xr scp 1 ,
 .Xr sftp 1 ,
Index: b/sshd.c
===================================================================
--- a/sshd.c
+++ b/sshd.c
@@ -55,6 +55,8 @@
 #endif
 #include "openbsd-compat/sys-tree.h"
 #include "openbsd-compat/sys-queue.h"
+#include "openbsd-compat/port-linux.h"
+
 #include <sys/wait.h>
 
 #include <errno.h>
@@ -214,6 +216,13 @@ struct {
 } sensitive_data;
 
 /*
+ * Every RESEED_AFTERth connection triggers call to linux_seed() to re-seed the
+ * random pool.
+ */
+#define RESEED_AFTER    100
+static int re_seeding_counter = RESEED_AFTER;
+
+/*
  * Flag indicating whether the RSA server key needs to be regenerated.
  * Is set in the SIGALRM handler and cleared when the key is regenerated.
  */
@@ -1400,6 +1409,11 @@ server_accept_loop(int *sock_in, int *so
 					startups++;
 					break;
 				}
+			if(!(--re_seeding_counter)) {
+				re_seeding_counter = RESEED_AFTER;
+				linux_seed();
+				audit_linux_prng_seed(rand_bytes, rand_file);
+			}
 
 			/*
 			 * Got connection.  Fork a child to handle it, unless